Solution Manual for Ecology Concepts and Applications Release 2025 Anna A. Sher and Manuel C. Molles

Solution Manual for Ecology Concepts and Applications Release 2025 Anna A. Sher and Manuel C. Molles 1. Answers to End-of-Chapter Review Questions 2. Answers to Critiquing the Evidence 3. Answers to Concept Review Questions

Answers to End-of-Chapter Review Questions Chapter 1 1. The advantage of dividing the field of ecology into subdisciplines, each focusing on a single level of organization is that such concentration and simplification tends to make the hypotheses addressed more likely to be testable.

2. The pitfalls of subdividing nature is that important ecological relationships may go unrecognized. Figure 1.1 misrepresents nature by converting the complexity of nature into an abstract simplification and by picturing the natural world as a vertically nested hierarchy, when in fact natural relationships and influences are more like a tangled web.

3. In the case of MacArthur’s warblers, you might compare the use of foraging zones by warbler species in areas with the full complement of warbler species with the use of foraging zones where one or more species is missing from the community. One way to test the role of competition in excluding some American redstarts from productive feeding areas would be to capture and remove the, presumably, dominant individuals from those areas to see if other redstarts, especially females and young males would move in to replace the individuals removed.

4. New technology allows us to see things we were not able to observe before, and ask questions that we were not previously able to address. For example, drones can carry cameras and other sensors to locations that are not easily accessible. Stable isotope analyses allow us to trace water and nutrients through ecosystems. Genetic analyses allow us to identify gut contents. Sound equipment allows us to hear things out of the range of human hearing.

Citizen science initiatives increase the number of eyes and ears collecting evidence.

Improved computing allows us to analyze larger data sets and run complex models to more accurately predict future events.

5. The species composition of these forests has changed substantially and their composition is likely to change in the future in response to climatic change.

6. There are trade-offs when comparing simple and complex models. While complex models include more data/variables and potentially provide greater accuracy, they may also incorporate more assumptions and therefore have a greater potential for error if any of those assumptions are invalid.

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1. Use biome discussions as a guide.

2. Use figure 2.8 and the associated discussion as a guide.

3. Use figure 2.4 and associated discussion as a guide. High precipitation in the tropics is produced by high rates of evaporation and subsequent condensation of water vapor in ascending air masses. The clouds formed in this way produce the heavy precipitation associated with the tropics. High precipitation at temperate latitudes is produced when warm moisture bearing subtropical air meets cold polar air, which forces condensation of the water vapor in the subtropical air mass. Many tropical environments experience drought during periods of El Niño (see chapter 23).

4. The seasonal rainfall of these biomes is produced by shifts in the latitude at which the sun is directly overhead. Figure 2.4a, which shows the sun directly overhead at the equator, which generates storms through the processes of evaporation, condensation and precipitation of water, is really a snapshot of a dynamic system. The latitude at which the sun is directly overhead, which is sometimes called the "solar equator", and acting as a generator of tropical storms shifts between 23.5° N and 23.5° S. The wet season comes during the warmer time of the year when the sun is more nearly overhead. The dry season comes when the solar input is less direct (sun's angle is more oblique).

5. Anywhere that the presence of mountains which can force precipitation in rising air masses and form a "rain shadow" in the leeward (downwind) side. The height of mountains will generally make a difference in the rain shadow effect, since higher mountains will induce more precipitation in rising air masses.

6. One of the greatest differences is the presence of permanent snow and ice on mountains at high latitudes.

7. One of the main differences between midlatitude and tropical alpine zones is that on tropical mountains daily variation in temperature is nearly as great as seasonal variation. Tropical alpine ecosystems lack fht every strong seasonality in input of solar radiation and temperature that occurs in midlatitude alpine zones.

8. In tropical climates the dominant seasonal change is from wet season to dry season. At very high latitudes it is cold much of the year with a brief cool growing season. In some tropical countries, such as Costa Rica, people have divided the seasonal changes significantly than has been done customarily in temperate climates. In the middle of the wet season, for instance, there is a period of reduced rainfall which Costa Ricans call veranillo, which means "little summer". The point here is that the seasonal terms associated with midlatitudes do not fit the annual variations that occur in other parts of the earth. It would be interesting to catalog the traditional terms for seasonal changes used by native peoples living in different climatic zones.

9. There has been much greater connection and exchange across the tundra and boreal forests which form nearly continuous bands in the northern hemisphere. In contrast, the temperate woodland tropical rain forest biomes are highly fragmented with few opportunities for biotic exchange over long periods of evolutionary history.

10. The most heavily impacted biomes have been temperate forest, temperate grassland, desert, and temperate woodland. Areas of tropical dry forest have also been fairly heavily impacted.

Tropical rain forest, boreal forest, and tundra have received less impact. Satellite imagery could be used to assess the density of human-induced change on landscapes. The very high rates of human population growth in tropical countries and increasing resource extraction in the northern biomes will likely increase human impact in these biomes.

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Chapter 3 1. Use Figure 3.2 as a guide for your review. The major sources of freshwater are groundwater, lakes, and rivers. A large amount of freshwater is also present as ice. Water shortages already affect large regions of the world and groundwater levels are dropping in many regions. Even where water remains plentiful, pollution is reducing water quality.

2. The proportion of the ecosystem receiving sufficient light to support photosynthesis is 200 m divided by 4000 m, about 0.05 or 5% of the total.

3. Major challenges faced by organisms moving from an aquatic to a terrestrial environment included lower support in the less dense aerial medium, greater temperature variation on land, and desiccating water loss to air. Some advantages were less resistance to movement through air, lower rate of heat loss to air, and higher oxygen concentrations.

4. Refer to figure 3.13 as you develop your answer. Darwin's developmental sequence was tested by drilling on atolls, which revealed deep accumulations of ancient coral reefs deposited on sunken volcanic mountains.

5. The main factor here is that, though urchins feed on young corals, they also suppress the growth of algae, which reduces algal competition with the young corals. Thus the net effect of urchins on coral establishment is positive.

6. The wide environmental fluctuations of the intertidal environment has probably selected for greater physiological tolerance among intertidal species. Because of differences in the intensity of selection, tolerance of variation in salinity should be higher in the upper intertidal zone compared to the lower intertidal and subtidal zones.

7. Because small grain size reduces rates of water flow, oxygen concentration is generally lower in the interstitial waters of fine sediments compared to coarse sediments. Oxygen concentrations should be lower in tide pools in sheltered locations because of wave-related circulation.

8. The most direct way to test these predictions would be to study the relative contributions of litterfall from streamside forests and photosynthesis within the stream to the total energy budget of the stream.

9. Two approaches have been used to study the influence of nutrient availability on lake primary production. The first has involved measuring nutrient availability and rates of primary production in a large number of lakes and looking for a correlation between these two variables. The second approach has been to increase the nutrient availability in lakes and measure primary production responses (see Chapter 18).

10. It is clear that that the introduction of exotic species has greatly altered the structure and functioning of the Great Lakes ecosystem. However, the Great Lakes of Africa have also been impacted by species’ introductions. See Chapter 17 online, which includes a discussion of the effects of introducing Nile perch on the rich fish fauna of Lake Victoria.

Chapter 4 1. Darwin mainly conducted comparative studies of natural populations, while Mendel conducted numerous experimental studies in his garden. In addition, Mendel used mathematics extensively in his work, while Darwin did not. Darwin proposed potential mechanisms for evolutionary change in species. Mendel discovered mechanisms of inheritance. The studies of Darwin and Mendel prepared the way for the later studies

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reviewed in this chapter by providing a mechanistic theory to explain evolution in organisms and the genetic transmission of characteristics between generations.

Genetic variation within and between populations is required for evolutionary change. On the surface, it is difficult to know if the phenotypic variation observed within and between populations is due to genetic differences and local adaptation, or phenotypic plasticity (identical genotypes producing different phenotypes when exposed to different environmental conditions). Common garden experiments can be used to help distinguish between these two sources of phenotypic variation. The observation of distinct differences between individuals from the same source population grown in different environments suggests phenotypic plasticity; while differences between individuals from different source populations grown in the same environment supports true genetic variation and local adaptation. An experiment showing consistent expression of a trait regardless of environment would support genetic variation and local adaptation rather than plasticity.

The Hardy-Weinberg principle states that in populations mating at random in the absence of evolutionary forces, allele frequencies will remain constant. Hardy-Weinberg equilibrium is the condition under which allele frequencies do not change as a result of the conditions assumed by the Hardy-Weinberg principle. The conditions required for Hardy-Weinberg equilibrium are random mating, no mutations, large population size, no immigration, and equal fitness for all genotypes within the population.

In the Hardy-Weinberg equation, p2, q2, and 2pq represent genotype frequencies. How these genotype frequencies translate into phenotype frequencies depends on the inheritance system.

Phenotype and genotype frequencies are not always the same.

Genetic drift is change in gene or allele frequencies in a population as a result of random processes. Genetic drift is most common in small populations and least likely in large populations. Genetic drift decreases genetic variation in populations, since it can eliminate alleles from populations.

In your breeding program, you should create a breeding population that incorporates as much of the genetic variation within the remaining population as possible.

Random mate selection with respect beak size in the population of G. fortis at El Garrapatero would tend to mask the influence of disruptive selection and even out the distribution of individuals across the range of beak size in figure 4.13.

Marlene Zuk, Robin Tinghitella, and their colleagues demonstrated rapid evolutionary adaptation to introduced parasitic flies when they discovered that non-singing males, which do not attract the parasitic flies, increased in frequency in the population following the introduction of the parasitic flies. Genetic drift reduced the genetic diversity of field crickets on the islands compared to mainland populaitons and, coupled with founder effect, may have increased the frequency of non-singing males in island populations. This set the stage for rapid increase of non-singing males following introduction of the parasitic flies.

Classical approaches to genetic studies, such as common garden experiments have the potential to reveal the significance or function of genetic differences among populations.

Meanwhile modern molecular techniques, such as DNA sequencing, reveal genetic differences or variation directly. The classical approaches require little in the way of technology. However, they are labor-intensive and require a great deal of time. Modern methods often require costly equipment but they are less labor-intensive and can yield results in a shorter time.

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Chapter 5 1. On Southern mountains, boreal plants and animals should be most prevalent at high elevations and on north-facing slopes, which are cooler than south-facing slopes.

2. During the warmest parts of the year, the beetle would likely avoid spending long periods of time on bare ground (see figure 5.3) in full sun. It could keep its temperature at 35°C by moving between sun and shade. During the hottest time of the day it might seek the shelter of a burrow. During the cooler times of the year the beetle would likely seek out full sun and be active during the warmest time of the day.

3. Although sharks and tuna are both fish, they are only distantly related. Their lineages diverged approximately 450 mya, and they did not inherit RM endothermy from a common ancestor. Endothermy is especially costly in aquatic environments due to the heat absorption and conductive capacity of water (significantly greater specific heat, and latent heat of vaporization in comparison to air). In order for this trait to be the result of natural selection (multiple times), the energetic benefits of endothermy in these animals must outweigh the costs. Endothermic fish are able to decrease the energetic costs through circulatory countercurrent exchange mechanisms. Additionally, they have been observed to swim faster and have generally larger ranges than comparably sized exothermic fish. This gives these large predatory fish significantly improved hunting efficiency and enough of a fitness benefit to have resulted in the convergent evolution of RM endothermy in sharks and tuna.

4. Because of declining enzyme function, swimming speed should decrease above 20°C. 5. These results leave open the possibility that reduced egg hatching at higher temperatures has interacted with other factors, such as competition with other snail species, rates of predation, or mortality due to disease, to produce local extinctions. We need to consider birth rates, death rates, and the balance between them.

6. Basking should be most prevalent among butterflies in cooler climates at higher latitudes.

Butterflies should also be more likely to be found basking in early morning than in the middle of the day.

7. A major disadvantage is greater vulnerability to predators when in torpor and slower behavioral response to environmental fluctuations generally.

8. Plants use orientation of their surfaces to increase or decrease heat gain. In addition, plants avoid temperature extremes by going into dormancy. The most obvious examples of this are the plants of temperature deciduous forests.

9. This example suggests that predation exerts strong selection for background matching, or camouflage, in these beetles. The broader implication here is that natural selection for one characteristic may be opposed to natural selection for other characteristics, which could place constraints on the ability of natural selection to optimize.

10. One of the reasons behind the mismatch between organisms and environment was the subject of Question 9. In addition, during selection, the present environment acts upon existing genetic variation within populations to produce differential survival and reproduction among genotypes. However, future environments may be quite different from past environments and if environmental change is too rapid or the genetic variation within populations too low, the population may become extinct.

Chapter 6 1. The higher humidity under stones reduces the gradient of water concentration from the isopod to the air and so reduces the rate of evaporation.

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2. The vapor pressure deficit is the difference between the actual water vapor pressure in air and the saturation water vapor pressure of air at a particular temperature. Osmotic pressure is the force necessary to prevent the movement of water down a gradient of water concentration.

Water potential is the capacity of water to do work. Since vapor pressure deficit, osmotic pressure, and water potential can all be measured as pressures, they can be expressed in the same units.

3. Lower leaf water potential at midday should increase the rate of water movement from soil to plant, since water moves down gradients of water potential.

4. The kangaroo rat obtains most of its water from metabolic water, while the beetle obtains most of its moisture from condensed fog. Compared to the beetle, the kangaroo rat loses a greater proportion of its water through urine.

5. Water loss rates should be higher among tenebrionid beetle species from moist temperate environments. This prediction is based on the assumption that there is some energetic cost associated with water proofing and that natural selection favors investment in water proofing where it increases the evolutionary fitness of individuals. One way to test this prediction would be to go out and measure water loss rates in tenebrionid species from different environments.

6. The need for water is a strong selective force for all organisms in arid environments, so individuals with variations in traits and behaviors that enabled them to collect more water would have improved fitness, and be more likely to pass those traits on to future generations.

The similarity of these water collecting strategies in such different species (convergent evolution), makes sense due to the physical properties of water. These properties dictate how water is collected via condensation, or moved from one location to another via channeling and gravity. Successful strategies to collect water used by plants and animals living in arid environments could potentially be ―mimicked‖ in order to collect water for human use.

7. Plants and animals must exchange carbon dioxide and oxygen with the surrounding air in order to engage in respiration and photosynthesis. Complete water proofing would eliminate these vital gas exchanges.

8. Use figures 6.26, 6.27 and 6.28 as guides. Marine bony fish are hypoosmotic (lower concentration of salts, higher concentration of water) relative to their environment.

Freshwater bony fish are hyperosmotic. The kidneys of marine and freshwater sharks would both function to pump excess water out of the environment but the kidneys of freshwater sharks would need to pump water at a higher rate.

Chapter 7 1. Ultraviolet light, while energy rich, is highly damaging to organic molecules including those involved in photosynthesis. The existence of vision systems which detect UV light suggests that a photosynthetic system capable of using UV light may be theoretically possible.

Infrared light has been generally considered to be too low in energy to drive photosynthesis.

The physiology of photosynthetic bacteria seems to indicate otherwise.

2. C3 plants are best adapted to cool and moist climates, where they should predominate, while C4 and CAM plants should predominate in arid and semiarid environments of high light intensity. Within a macroclimate, some microclimates would tend to favor one or another of these groups of plants. In addition, one must consider seasonal variation and longer-term variation (e.g., drought cycles) in climate.

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3. At low CO2 concentrations, C4 plants are better at conserving water, since PEP carboxylase, the main enzyme involved in concentrating CO2 in C4 plants, has a high affinity for CO2.

4. Herbivores generally consume food that is abundant but well defended. Detritivores consume food that may be even more abundant than the green tissues eaten by herbivores but detritus is often low in some essential nutrients, especially nitrogen. Carnivores consume foods high in nitrogen but that is generally very well defended. Omnivores were the main organisms left out of the discussion.

5. The main advantage of advertising is that it reduces the probability of attack by predators.

Mullerian mimicry increases the abundance of similar-looking noxious individuals in the environment, which reduces the probability of attack on any particular individual by a "naive" predator. In Batesian mimicry, the mimic reduces its probability of being eaten (a benefit) but the risk to the model is increased because of the existence of palatable individuals that display warning coloration to potential predators.

6. Begin by choosing one or more chemosynthetic autotrophs and building the rest of the biota on this foundation.

7. Type 1: filter feeding aquatic organisms that feed on small prey; Type 2: consumers limited by prey availability at low prey densities and by prey handling time at high densities; Type 3: predators that require some learning to be effective on a prey species and/or that feed on prey that is well protected at low densities. Selection for prey defense should lower the height of functional response curves, while selection for more effective predators should raise the height.

8. Specializing on crayfish (which has apparently occurred) would increase the rate of energy intake E/T. 9. Allocation to roots versus shoots influences the rates of nutrient uptake by roots versus energy fixation by photosynthesis by shoots. Balancing these two processes may require different levels of investment in roots versus shoots in different environments.

Chapter 8 1. The idea here is to use the descriptions of mating behavior and physical characteristics of species described in the introduction to make predictions about sexual selection. For instance, the chapter opens with schooling fish that are identical in morphology. The absence of obvious features that distinguish males and females suggests that predation on the species overrides potential sexual selection for dimorphism. In the second example, damselfish males compete with other males for territories, which suggests intrasexual competition for spawning territories. This competition should act as a source of intrasexual selection. Though the example doesn't mention how females choose males, they may distinguish between males on the basis of territory quality and/or male characteristics, such as coloration, size, and so forth. Female choice of male damselfish should create the conditions for intersexual sexual selection. Use a similar approach to predict the forms of sexual selection occurring in each of the remaining species described in the introduction.

2. Within a population of a species that reproduces sexually, there are often complex social behaviors associated with either attracting or choosing mates. In a species having separate sexes, there are often male-specific and female-specific mating behaviors. However in a hermaphroditic species all individuals should exhibit male and female forms of social behavior. As the number of forms of males or females increase in a population, the diversity of behavioral interactions within the population will likely increase.

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3. Physical factors that might influence the color of male guppies include the turbidity of the water, the color of the materials forming the bottom or banks of the stream, and the quantity and quality of light shining onto the stream.

4. The greenhouse experiments provided the opportunity to control several factors within the experimental environment, while varying the factor of interest, intensity of predation. The shortcomings of the greenhouse experiments were that many other factors of potential importance to guppy coloration, for instance a wide variety of invertebrate predators or a diverse diet that includes a wide variety of invertebrate prey, were absent in the greenhouse environment. Field experiments give the scientist less control over environmental conditions.

However, if carefully designed, field experiments reduce the chances of experimental artifact. Ideally, the ecologist uses several sources of evidence when exploring a natural phenomenon.

5. There is evidence for intrasexual and intersexual selection in scorpionflies. For example, competition among male scorpionflies can result in injuries during fights, a strong indicator of intrasexual selection among males in competition for nuptial offerings. Intersexual selection is suggested by mate selection by female scorpionflies, which appears to be mostly mediated by the quality of nuptial offerings presented by males from which females get nutritional benefit.

6. The maternal plant may influence the rate of growth by pollen tubes of different genotypes, creating conditions that increase the probability of successful mating by some pollen types over others. The maternal plant may also invest more energy resources into some seeds pollinated by particular pollen genotypes, while reducing energy allocated to other seeds.

Maternal plants may even selectively abort seeds based on their paternity. Competition among pollen may take the form of a race, determined by rate of pollen tube growth, or involve some type of interference among pollen on the stigma.

7. Jennifer Jarvis waited one year after establishing her laboratory colony of naked mole rats before attempting to quantify the behavior of the laboratory population so that she could be sure that the colony had adjusted to the laboratory environment If Jarvis had begun her studies soon after the colony was established, her results may have been strongly influenced by atypical behaviors associated with adjustment to the new environment.

8. Eusociality is generally thought to include three major characteristics: 1) Individuals of more than one generation living together, 2) cooperative care of young, and 3) division of individuals into sterile, or nonreproductive, and reproductive castes. Naked mole rats show all three of these characteristics.

9. Use the many case histories of laboratory and field studies discussed in this chapter as models for your proposed study.

Chapter 9 1. The highly reflective leaves of Encelia farinosa reduce heating of leaves and lower the rate of water loss. The deeper penetrating roots of E. frutescens provides access to deeper groundwater, which sustains transpiration sufficient to evaporatively cool the plant’s leaves.

2. Spruce trees in the desert mountains of North America are concentrated at higher elevations and on north facing slopes, because temperatures are lower and precipitation greater at high elevations and temperatures and evaporative water losses are lower on north facing slopes.

3. Figure 9.10 summarizes the answer to this question.

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4. If plants are distributed mainly in response to the distribution of soil characteristics, there should be a strong correspondence between the distribution of soil characteristics and the distribution of individuals within a plant population.

5. The plant reproducing from seeds should have a less clumped distribution pattern compared to the plant species reproducing mainly by budding.

6. Assuming that the habitat could be restored, the refuges should be established in areas that once supported high densities of fish crows (historic hotspots). Several refuges should be stocked simultaneously in case one or more fails.

7. Mammals tend to have higher densities than birds of similar size. Terrestrial invertebrates tend to live at lower densities than aquatic invertebrates.

8. Consult figure 9.22. Species that have an extensive geographic range, broad habitat tolerances, and large local populations are the least vulnerable to extinction, while those with restricted geographic range, narrow habitat tolerance, and small local populations are the most vulnerable.

9. Yes, at least somewhat since large organisms tend to live at the lowest population densities, they automatically show at least one aspect of rarity. However, size of geographic range and habitat tolerances are not included in the analyses by Damuth and Peters and Wassenberg.

Chapter 10 1. Use the discussion in this chapter to construct your outline of Muller's colonization cycle.

One of the best ways to follow the colonization cycle of an organism like N. latissima would be to mark the shells of a large number of individuals in the colonizing waves and use other marks to identify individuals in local stationary populations.

2. A cohort life table is made by identifying a large number of individuals born at about the same time and following them from birth to death and recording the age at which each individual dies. One of the main assumptions of a cohort life table is that your cohort is representative of the population as a whole. A cohort life table is most practically used when it is possible to observe and keep track of a large number of individuals born nearly simultaneously. A static life table is constructed by recording the age at death for a large number of individuals in a population. The individuals in a static life table are not all part of a cohort. A static life table assumes that...

3. Type III survivorship is difficult to study because of the large number of individuals that must be studied to adequately record mortality during the very early portion of the life cycle.

4. It is reasonable to assume that most species with very high reproductive rates have type III survivorship because otherwise their populations would be growing at extremely rapid rates.

5. A population with highly episodic reproduction will often show an age structure with age classes, often early age classes, missing. These reproductive failures may suggest that the individuals in a population are not replacing themselves and that the population is dying out.

In some populations, of desert shrubs for example, significant reproduction occurs every few decades. The best way to avoid such misinterpretations is to conduct long-term population studies and where possible to do historical reconstructions of population structure and reproduction.

6. The main point here is that while Leverich and Levin accurately measured the reproductive and mortality rates of the 996 individuals in their study, these 996 individuals were a sample of a much larger population. Therefore, the population statistics for this sample of 996 individuals were estimates of those parameters for the larger population.

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7. R0> 1.0 is growing, R0 = 1.0 is stable, R0< 1.0 is declining, r > 0 is growing, r = 0 is stable, r < 0 is declining.

8. The minimum information needed to construct a life table and fecundity schedule are lx, the proportion of the population surviving to each age x, and mx, the average number of offspring produced by each individual at each age x.

9. In a predator population increasing in density in response to increased prey density r will be greater than 0 and R0 will be greater than 1. Because prey availability can affect survivorship, lx, and reproductive rates, mx, as well as R0, a predator population undergoing a strong numerical response (i.e., growing rapidly) may also show an altered generation time, T. Chapter 11 1. The geometric model of population growth is appropriate for organisms with nonoverlapping generations. The exponential model of population growth is most appropriate for organisms that have overlapping generations.

2. You would need to know more about relative reproductive rates. In fact, the much longer interval between births among north Atlantic right whale populations, every 4 to 7 years compared to every 2 years for gray and blue whales, indicate a very low potential rate of population growth. Consequently, these whales can be expected to increase very slowly even with full protection from whaling.

3. To build the logistic model for population growth from the exponential model, first substitute rm, the intrinsic rate of increase which is a constant, for r, the per capita rate of increase which is variable. Next, take the resulting expression for exponential grow, rmaxN, times 1N/K. This last factor, 1-N/K, produces sigmoidal growth. See figure 11.13 for further explanation.

4. The factors that limit population size are those aspects of the environment that affect birth and death rates in populations. These include environmental factors such as limited habitat, food availability, predation, disease, parasites, and so forth. Make this listing more concrete by listing the limiting factors for a specific organism that you know something about or about which you can readily obtain information.

5. The per capita rate of increase, r, is an actual rate that varies with environmental conditions.

The intrinsic rate of increase, rmax, is a theoretical rate of increase for a population of an organism increasing at a maximum rate under "ideal" conditions for the species. You can estimate the rm of a species experimentally by providing ideal conditions for population growth and measuring rates of increase.

6. Biotic factors limiting population growth include competition, predation, disease, and parasitism. Abiotic factors that limit population growth include fire, drought, excessively high or low temperatures, floods, toxins, and so forth.

7. Because they are capable of killing all vulnerable individuals, an abiotic factor such as a severe freeze can influence populations independently of local population density. In contrast, the proportion of a population attacked by a predator or infected by a disease organism usually changes with the density of the attacked or infected population. Typically density independent factors may be at least partially influenced by population density if, for instance, there are a limited number of safe sites that can be filled, leaving the remainder of the population more vulnerable. For instance, at high population densities individuals in a population may move into floodplain habitats where they are more vulnerable to floods.

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8. See figure 11.23. Human population density tends to be highest in coastal regions and lowest in the interior of continents and in the Arctic and Antarctic. Very few regions are completely devoid of human inhabitants. Population growth is fastest in developing countries such as Rwanda and approximately stable in many developed countries such as Japan and many countries of Western Europe. Many developed countries have declining populations.

9. The projected global population in 2050 is over 9 billion. This population size may not be sustainable over the long term because the resource requirements of such a large population may damage the environment (e.g., change atmospheric composition, pollute freshwaters, destroy forests, deplete fish stocks) to such an extent its capacity to support humans will decline. Such a population might persist over the long term if average per capita resource consumption is greatly reduced.

Chapter 12 1. Advantages associated with producing small seeds include those associated with producing greater numbers of offspring. More numerous offspring would be advantageous in species that live primarily in highly disturbed environments, where the probability of survival for young is low and where dispersal among disturbed sites is advantageous.

2. This question is related to Question 1 but here you should include animals as well as plants in your answer. An additional factor to consider for animals is the relative investment in parental care. Among fish for instance, parental guarding of eggs and young is common among species living on reefs but does not occur among fish living offshore in open waters.

In these offshore populations, juvenile survival is very low which favors producing large numbers of young.

3. Growing from larger seeds could give an advantage to seedlings facing strong environmental challenges to their establishing by providing energy reserves that make the young plant less dependent on current environmental circumstances. These energy reserves allow the developing plant to grow to a larger size which pushes the leaves up higher in the environment, an advantage where competition for light is intense. Extra energy reserves also allow the young plant to develop a more dense root network, an advantage where competition for nutrients is significant.

4. The authors were addressing questions related to broad patterns of variation among species.

Therefore providing a solid answer to the questions they posed required including information on a large number of species. Since it would be impossible for the authors to perform original research on so many species within a reasonable time period, they had to rely on data from published studies.

5. Variation within a species will generally be less than variation among species.

6. To live in an environment of high stress and high disturbance, an organism would need to have a high degree of tolerance to extreme environmental conditions and be capable of recovering rapidly following frequent periods of disturbance. The organisms most typically found in such environments are bacteria. Viruses can also persist under such conditions but they are often not considered to be "organisms."

7. Rio Grande cottonwoods have a life history that corresponds most closely to the periodic life history proposed by Winemiller and Rose.

8. The point here is to bring together the information on trade-offs between seed size and seed number and Grime's classification of plant life histories summarized in figure 12.20 with patterns of seed size seen in plants with different growth forms and dispersal strategies. Since

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figure 12.8 provides information on seed size, the relative numbers of seeds produced by these categories of plants follows directly. In general plant growth forms, or dispersal strategies, associated with producing small seeds are also generally associated with producing many seeds. Meanwhile those plants producing large seeds, generally produce fewer.

9. To apply Winemiller and Rose's model (figure 12.21) to plants, you would need to know the survivorship, fecundity or seed production, and age at maturity of the plants included in your analysis. You would need to have this information for many plant species.

Chapter 13 1. Here are some suggestions. Use a fast growing herbaceous plant species such as radish or rye grass. Small pots to medium sized pots would be most convenient. A commercial potting soil with known quantities of nutrients or no nutrients would allow you to manipulate nutrient availability through additions of fertilizer. Plant performance could include average plant mass after some specified period of time, number of seeds, seed size, and so forth. I suggest planting in three densities: 1, 10, and 100 plants per pot (plant somewhat more seeds than this and then thin to these densities).

2. Controlled experiments give us indications of what is possible in nature. To improve the correspondence to the natural situation, use wild species under study in natural environments, include natural densities, nutrient levels, and light intensities in your range of experimental conditions, and so forth.

3. The common observation of self-thinning in plant populations indicates that intraspecific competition among plants for resources such as water, light, and nutrients is intense enough to cause mortality in natural plant populations.

4. The niches of carnivores, such as canids or felids, might be represented as prey size. This means of representing carnivore niches is supported by the observation that predators are usually size selective and that predator body size usually correlates well with prey size. The niches of plants may be represented by their growth form, whether they are annuals or perennials, their relative investment in roots and shoots, their degree of shade tolerance, and whether they employ C3, C4, or CAM photosynthesis.

5. Species that overlap a great deal in their fundamental niches have a high probability of competing because they have very similar ecological requirements. Overlap in ecological requirements is the main basis for competition. If species overlap a great deal in their realized niches and live in the same area they probably do not compete significantly. If they did, one would likely competitively exclude the others. In cases such as this, factors such as disturbance or predation may be keeping the populations of the potential competitors low enough so that they do not deplete resource supplies sufficiently to produce resource shortages.

6. Use figure 13.14 as a guide to answer this question.

7. The amount of food that Gause provided was apparently the factor that limited paramecium population size. In other words, food availability determined carrying capacity. With lower food availability, the growing populations of paramecia depleted food supplies more quickly and competition for limited food supplies became intense in a shorter period of time.

8. The beetle T. confusum had the competitive advantage under cool, dry conditions. The beetle T. castaneum had the competitive advantage under hot, humid conditions. Park could not

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predict the outcomes of his competition experiments with complete certainty. This suggests that the outcome of competition in nature may be often unpredictable.

9. Niche partitioning among parasitoids attacking caterpillars could have evolved through selective pressure to avoid interspecific competition. Those parasitoids choosing to attack different sizes of caterpillars compared to their potential competitors would have greater reproductive success than individuals attacking the same sized caterpillars as their competitors and would have higher reproductive fitness as a consequence. The genetic contribution to size selective host choice, versus plastic behavioral response to the presence of a competitor, could be tested by rearing parasitoids in isolation from potential competitors and providing access to large and small host caterpillars. If their host selection is under genetic control, they would select the same host sizes as usual, even in the absence of competing species.

10. Competition seems most likely in more stable environments with low rates of disturbance and predation. Competition seems less likely where populations are subject to frequent and intense disturbance or where they are heavily exploited by predators or other consumers.

Field experiments along disturbance or predation gradients could be used to test these ideas.

Chapter 14 1. Predators kill and consume other organisms. Herbivores consume live plant material but do not usually kill plants. Parasites live on the tissues of their host but not generally killing it.

Pathogenic organisms induce disease, a debilitating condition, in their hosts.

2. Both spiny headed worms and the rust Pucinia monoica manipulate their hosts in ways to promote their own survival and reproduction. Spiny headed worms change the behavior of their hosts, while the rust Pucinia monoica manipulates the growth form of its plant host.

3. In the absence of the parasite, the predatory beetles reduce the fitness of the competing beetle species more than they affect their own fitness. However, in the presence of the protozoan parasite Adelina tribolii the predatory beetles infect themselves with a debilitating parasite and so reduce their own fitness more than that of the other beetle species.

4. We know that various environmental factors must control populations because natural populations almost never realize their full potential for increase.

5. The actual and potential roles played by parasites and pathogens in controlling natural populations is becoming more and more apparent. However, they have been more difficult to study than predator-prey interactions. Modern tools provided by molecular biology have made studies of parasites and pathogens more feasible.

6. By eliminating the most heavily infected individuals in the prey population, predators may reduce the overall level of infection in the prey population thereby reducing mortality rates in the prey population.

7. As hare populations increase, they reduce the quantity and quality of their food supply.

Reduced food availability, which leads to starvation and weight loss, reduces population size.

This potential decline is accelerated by high rates of mortality due to predation. Once hare populations are reduced, plant populations recover, and the stage is set for another increase in the hare population. As hare population density is reduced, predator populations decline in turn and increase again only after the hares are again abundant.

8. Mathematical and laboratory models have provided a conceptual basis for studies of predator-prey cycles in nature. The disadvantage of mathematical and laboratory models is that they can be unrealistic. The advantages of mathematical and laboratory models are that

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they provide the researcher with greater control and greater freedom for manipulation to explore what is possible.

9. Prey can avoid predators simply by being active when their predators are not. Mayflies can feed any time of the day in the absence of fish. However, when fish are present, there is strong selection to be active at night when the fish do not feed as much. However, there may be strong preference among the fish studied by Culp and Scrimgeour for large mayflies. If so, there has probably been strong selection for modifying daily rhythms by larger but not smaller mayflies.

Chapter 15 1. Some of the key mutualisms contributing to ecological structure and function of the biosphere include the mutualisms involved in pollination, seed and fruit dispersal, cellulose digestion in animals, nitrogen fixation by plants, mycorrhizae, and zooxanthellae-marine invertebrate relations. There are many others.

2. Mycorrhizae increase the uptake of nutrients and water by plants. Plants provide energy rich organic compounds in the form of root exudates. When Hardie removed the mycorrhizae from some of her study plants, their rate of transpiration decreased. She hypothesized that mycorrhizal fungi increase plant access to water by providing more surface area for absorption of water.

3. Use figure 15.5 to construct your outline. The strongest evidence that artificial fertilizers may select for less mutualistic mycorrhizal fungi was that plants inoculated with mycorrhizal fungi from fertilized soils produced fewer inflorescences.

4. The ancestors of mycorrhizal fungi may have been parasites that attacked plant roots to exploit root exudates and provided nothing to the plant in return. By chance a mutation could have appeared within a population of these fungi that induced translocation of nutrients from the fungus to the roots. If this exchange increased the plant's photosynthetic rate and the fungi's access to energy, natural selection could have favored this and subsequent mutation(s) that eventually turned an originally parasitic relationship into a mutualistic one.

5. The main manipulation used by Janzen was to remove ants from some swollen thorn acacias and then compare the growth, survival, and herbivore populations for acacias with and without ants (See figs. 15.9, 15.10, & 15.11).

6. The major difference between these two ant-plant mutualism is a much higher degree of flexibility in the relationship between ants and the aspen sunflower, Helianthella quinquenervis. Greater environmental variation may be the main factor selecting for flexibility in temperate ant-plant mutualisms.

7. The main similarities between the coral-centered and plant-centered mutualisms we discussed are that they both are organized around energy, nutrients, and protection, key factors in the lives of organisms. The major differences are the identities of the organisms (e.g., corals versus plants, crustaceans versus insects), and the types of environments (terrestrial versus aquatic).

8. The main benefit specified by Keeler's model is protection from herbivore damage; the main cost is investment in nectar protection by the plant. Keeler presents this mutualism from the plant's perspective. From the ant's perspective, costs might include probability of being eaten by a predator while tending the plant, while the benefit would be the increase in food intake

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due to feeding on the plant's nectaries versus their intake from other potential sources of food.

9. See the Lotka-Volterra equations in chapter 13. These could be changed to models of mutualism by substituting mutualism coefficients for the competition coefficients. A mutualism coefficient would summarize the positive contributions of individuals of the mutualist population and so the second minus sign in the equation would be replaced with a plus sign. The result would be a population dynamic model.

10. Humans observing the relationship between the honeyguide and honey badger could have begun to imitate the badger. Honeyguides that guided these solicitous humans may have had more ready access to bees' nests because of the greater resourcefulness of their new human mutualists.

Chapter 16 1. A community is an association of interacting species. A population is a group of individuals of a single species inhabiting a specific area. Community attributes include the number of species, the relative abundance of species, and the kinds of species comprising a community.

A guild is a group of organisms that all make their living in a similar way, for examples, the seed-eating animals in an area of desert, the fruit-eating birds in a tropical rain forest, or the filter-feeding invertebrates in a stream. The life-form of a plant is a combination of its structure and its growth dynamics. Plant life-forms include trees, vines, annual plants, sclerophylous vegetation, grasses, and forbs.

2. Use figures 16.3 and 16.4 as guides for drawing a lognormal distribution.

3. Species richness is the number of species in a community. Species evenness is the relative abundance of species in a community. The value of the Shannon-Wiener diversity index (H') increases directly with both species richness and species evenness. Greater species richness increases the length of rank abundance curves. Greater species evenness reduces the slope of rank abundance curves.

4. MacArthur attempted to represent the trophic niches of warblers as their use of vertical foraging zones in forests. Tilman represented the trophic niches of diatoms based on their nutrient requirements. It is important that the ecologist be familiar with the niches of study organisms before exploring relationships between environmental complexity and species diversity to assure that the complexity of the relevant environmental factors will be measured.

5. One approach to determine which environmental factors influence variation in bird species diversity across Patagonia would be to first document where bird diversity is higher and where it is lower. Next, study how birds in these areas use space, food, and other resources and then explore the data set for systematic variation in these factors along the bird diversity gradients of the region.

6. If disturbance is frequent and intense, the community will consist of those few species able to colonize and complete their life cycles between the frequent disturbances. If disturbances are infrequent and of low intensity, the community will be eventually limited to the few species that are the most effective competitors. The major assumption of the intermediate disturbance hypothesis is that natural selection will not be able to maximize both competitive and dispersal abilities.

7. The intermediate disturbance hypothesis suggests that in most cases, stabilized river flows should lead to decreased diversity of the river community.

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8. Disturbance of tropical rain forests by early human populations was much lower in both frequency and intensity compared to modern disturbance. The intermediate disturbance hypothesis would predict that recent disturbances threaten the biological diversity of these forests, while earlier disturbances apparently did not, because with the advent of the chainsaw and the bulldozer and increased human population size, human disturbance of rain forests has moved from intermediate to high levels.

9. Some of the key design features that would foster higher biological diversity would be including a high percentage of the landscape in natural vegetation and well-vegetated urban and suburban parks. You could also encourage residents to grow diverse native vegetation in their home gardens.

Chapter 17 1. Winemiller included the most common fish species that together represented 95% of the total number of individuals in his samples of the community. He excluded all species in the remaining 5% of the community. Paine defined a strong interaction as one that has a significant influence on community structure.

2. Keystone species are those that, despite low biomass, exert strong effects on the structure of the communities they inhabit. The keystone species in the intertidal along the west coast of North America and in New Zealand is a starfish, and both intertidal communities include a mussel as an important competitor. However, the New Zealand intertidal community included a large brown alga as an important competitor.

3. Lubchenco found that the preferred food species of the intertidal snail Littorina littorea, ephemeral and tender algae such as Enteromorpha spp., dominate tide pool algal communities in the absence of Littorina or where the snail lives at low population densities.

She also found that algal species diversity is highest in tide pools with intermediate densities of Littorina. In addition, Lubchenco found that the influences of Littorina are different in different parts of the intertidal zone.

4. As figure 17.14 shows, the fish in the food web studied by Power, especially steelhead, feed on predatory insects roach fry, and stickleback fry, all of which prey on chironomids. Thus, in the absence of predaceous fish, chironomids were subject to heavier predation pressure and their populations declined.

5. The species subject to strong feeding interactions, as indicated in figure 17.5, would be the most affected by the removal of Cyanistes caeruleus.

6. Answers may vary, however one suggestion could be that it would be useful to monitor predation pressures when making decisions about which species of parasitoid might provide the best biological control of cabbage worms. It will likely depend on which species of worm and hyperparasitoids are present in the system. In systems with high predation pressure from hyperparasitoids, C. glomerata may be the better choice, as this species has been shown by Vyas et al. to have higher survivorship under these conditions. In systems with lower predation pressure, C. rubecula may be more effective. In the long term, it might be best to dynamically adjust the parasitoid species in response to the presence or absence of hyperparasitoid species.

7. Viruses and other pathogens certainly have the potential to have major influences on community structure. Parasites may also influence community structure despite their relatively low biomass in many cases.

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Chapter 18 1. A population ecologist might study the distribution and abundance, rates of population growth, rates of reproduction, or dispersal of a particular species. A community ecologist would be more focused on patterns of species diversity, food web structure, how keystone species or physical disturbance influences species diversity and composition. An ecosystem ecologist studying the same forest would be concerned with processes such as primary production, energy flow, and nutrient cycling.

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2.

Forest Type

3.

4.

5.

6.

7.

8.

Annual Length of Growing Monthly NPP Season NPP (t/ha/yr) (Months) (t/ha/mo) Boreal forest 8 3 2.7 Temperate forest 13 6 2.2 Tropical forest 20 12 1.7 Compared to an annual perspective, this short-term perspective of primary production in high-, middle-, and low-latitude forests shows that during their shorter growing seasons, the monthly rate of primary production is higher in boreal and temperate forests.

From the perspective of migratory birds, temperate forest is probably the more productive.

While the experiments of Shaver and Chapin showed that nutrient additions can increase primary production in tundra, the production of fertilized plots is still nowhere near that of tropical rain forest.

The strength of the food web approach is that it preserves the trophic behavior of individual species but, as we saw, food webs include so much detail that they quickly become difficult to interpret. Lumping of species into trophic levels, as in chapter 18, simplifies the distribution of energy within the ecosystem. However, for some interests, this approach may oversimplify ecosystem structure.

The concentration of 13C in the tissues of the major food sources in the two forests and in the tissues of the small mammals will provide an estimate of the relative energy contributions of the riverside forest and the semidesert grassland (See figure 18.20).

The two concepts are very similar. They differ in the focal responses. The keystone species concept is focused on the effects of keystone species diversity and composition. The trophic cascade model predicts the effects of consumers on abundance or production of animal trophic groups and rate of primary production.

A comprehensive study would include studies of potential relationships between nutrient concentrations and primary production in a large series of tropical lakes and large- and smallscale nutrient enrichment experiments.

Chapter 19 1. Carbon is the element common to all organic molecules, and energy enters ecosystems through the process of carbon fixation. Nitrogen and phosphorus are also key constituents of biomolecules, such as DNA and amino acids, and they often occur in relatively short supply.

2. Because animal tissues are free of cellulose and lignin and high in nitrogen, they generally decompose at a relative rapid rate.

3. As shown in figure 19.8, rate of decomposition increases with increased actual evapotranspiration. Consequently, rate of decomposition is generally higher in ecosystems with high AET (e.g., tropical rain forests) and lowest in ecosystems with low AET (e.g., tundra). To test your hypothesis, you could set out a series of mesh bags containing a standard plant tissue in a series of these ecosystems and measuring the rate of mass loss.

4. Identify a series of soils exposed to similar microclimates and macroclimates and set out standardized plant tissues (e.g. oak leaves taken from the same tree) in the series of sites. If Melillo and his colleagues were correct, you should observe higher rates of mass loss on the fertile soils.

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5. These changes should generally increase nutrient spiraling length.

6. Higher rates of primary production and plant biomass should increase the capacity of a forest ecosystem to regulate nutrient losses from stream catchments. Low vegetative biomass and low primary production likely reduces the influence of desert vegetation on nutrient losses from desert catchments.

7. Plant biomass passing through the digestive tract of a large grazing mammal would generally break down at a faster rate because it is highly fragmented, partly broken down by the animal's digestive system, and relatively nutrient rich. The disappearance of the large grazing mammals from the savannas of east Africa would likely decrease the rate of nutrient cycling in the savanna ecosystem.

8. Nutrient enrichment of the Fynbos may lead to increased primary production but decreased plant diversity due to increased competition for fewer limiting nutrients (see figure 16.16).

9. Inputs at the rate of 0.2 kg/ha/yr would replace the loss of 21 kg in 100 years. At the rate of 17% loss per burn, approximately two thirds of the phosphorus would be lost in just seven burns.

Chapter 20 1. Foliage height diversity, which MacArthur found to be positively correlated with bird species diversity (See figure 16.10) generally increases with forest succession, at least over the 150 years of succession represented by Johnston and Odum's study sites.

2. With more time, the alga should dominate increasing amounts of space on the study boulders, and species richness on the boulders should decrease somewhat.

3. Early theories about succession in Glacier Bay were based on a chronosequence -a series of communities representing a range of ages or times since disturbance. Assumptions were made that any changes in the communities at the various sites was due to the relative age of those sites, and that the communities at younger sites would eventually progress through successional stages to resemble older sites, given more time. This idea was not supported by later empirical studies of the same plots. These studies suggest that species composition at these sites was less deterministic than expected, and depended more on which species happened to reach a location first. Subsequent research and observations in other locations and systems have continued to support the idea that the results of succession are not always as predictable as was initially proposed. Scientific ideas are always based on the best evidence available at the time, and are subject to change with new observations and evidence.

It is important to question the general applicability of observations and conclusions reached from one study by replicating experiments and testing those ideas in different situations.

Even though early models have been disproven in many cases, they did serve as an inspiration to conduct further studies that have resulted in today’s improved understanding of these processes.

4. The major assumption of studying chronosequences, the space for time substitution approach, is that the differences between communities of different ages undergoing succession in different places are essentially the same as those that would occur during succession on a single site if that site was studied over a long period of time. The rapid pace of succession in Sycamore Creek offers the ecologist the possibility of studying full successional sequences.

5. Frequent flooding should select for rapid life cycles in Sycamore Creek. Selection for rapid life cycles should be less intense in a stream that floods less frequently. In streams with

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6.

7.

8.

9.

longer interflood intervals, recovery of the community following flooding should be slower due to the slower life cycles of the species making up the community.

The tolerance model suggests that all species in the community are capable of colonizing a newly disturbed site and that early colonizers do not change environmental conditions in ways that facilitate the colonization of other species. Faster growing species tend to dominate early on in the process, and later successional species are those that grow more slowly but are also more tolerant of the increasing intensity of competition. Recent studies of Glacier Bay suggest that species composition appeared to be based on what species happened to reach a location first as each of the species found to dominate specific sites (Salix, Alnus, and Picea) are capable of excluding other seeds from colonizing once they become established.

The rate of succession should be slower in the areas nearest the volcanic blast, where the level of disturbance was greatest.

The frequent extinction of species over geologic time suggests that the species composition of climax communities is not very stable over long periods of time.

A frequently disturbed community/ecosystem would likely be dominated by weedy species capable of rapid colonization, establishment and reproduction. Such species would be most likely to survive and thrive in a highly unstable environment. The future biosphere, if disturbance increases in frequency and intensity, may be dominated by such species.

Chapter 21 1. Ecosystem and community ecology are generally focused on understanding a particular type of community or ecosystem. Landscape ecology aims to understand the exchanges that occur between the different types of ecosystems within a landscape and the forces that control the distribution and dynamics of those ecosystems.

2. Landscape 1 should contain a greater number of forest interior species since the patches in this landscape have a higher ratio of interior to edge and a greater area of interior habitat available for colonization by forest interior species.

3. Landscape 3 is more likely to be dominated by forest edge species.

4. Larger patches should be associated with higher rates of exchange of individuals among patches in a landscape. Therefore, rates of movement should be higher in landscape 1 (Assuming that the distances between patches in this hypothetical example do not inhibit movements of the small mammals in this landscape).

5. The main point here is that smaller organisms such as insects will have more space available to them than larger organisms such as birds.

6. The size of the manipulation by Diffendorfer et al. (1995) would probably have had little effect on the highly mobile birds of the prairie. However, the movements of the much less mobile ground dwelling beetles may have been strongly affected by the scale of their manipulation.

7. Figure 21.23 provides several examples of animals that affect landscape heterogeneity. The intermediate disturbance hypothesis is more concerned with the effects of disturbance on species diversity. Landscape ecology is more concerned with the influences of such species on landscape structure.

Chapter 22 1. The plot of the logarithms of area and species number should yield the tightest relationship between area and species richness.

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2. For a given area, far islands consistently support fewer species than near islands.

3. Several species may have colonized each of the islands and subsequently became extinct during the interval between the two studies, and so, as Diamond points out, his study probably underestimated species turnover on the California Channel Islands during this period.

4. Yes, this equality is predicted by the equilibrium model of island biogeography, which predicts that the number of species on an island will be the result of a balance between species immigration and species extinction.

5. According to the equilibrium model of island biogeography, island 1, the near island, should be subject to higher rates of immigration. The original equilibrium model predicts that rates of extinction should be approximately equal on the two islands. However, the rescue effect, demonstrated by Brown and Kodric-Brown, predicts lower extinction rates on the island nearer the mainland.

6. According to the equilibrium model of island biogeography, the two islands should be subject to approximately equal rates of immigration. However, the more recent target hypothesis predicts higher rates of immigration to island 1, the larger island. The equilibrium model predicts higher rates of extinction on the smaller island. MacArthur and Wilson suggested that rates of extinction should be higher on small islands due to smaller population sizes. Extinction rates might also be higher because of the smaller number of suitable habitats on small islands.

7. The major hypotheses proposed to explain the higher species richness of tropical regions compared to temperate and high-latitude regions are listed in chapter 22. Use this discussion to formulate your answer to this long-standing question in geographic ecology.

8. Larger areas should reduce extinction rates by allowing for larger geographic ranges and larger total population size. Large area should also facilitate speciation since on a large continent there is a higher probability of forming significant geographic barriers and initiating allopatric speciation. Figure 22.20 shows that number of species increases with continental area. As figure 22.18 shows, there is more land surface in the tropical zone than in any other latitudinal zones.

Chapter 23 1. Studies of competition and forest succession involved small numbers of species inhabiting relatively small areas, such as a few square meters of the intertidal zone or a single glacial valley. These earlier studies were much more easily pursued by a small group or a single individual. The large scale and greater complexity of global scale problems require larger teams of individuals representing a greater breadth of scientific disciplines.

2. Some of this question was already addressed in Question 1. It is safe to say that geologists, atmospheric scientists, and oceanographers will play key roles in the development of global ecology. Scientists from these disciplines teamed with ecologists would make effective teams for studies of global ecology, where ecologists have a critical role to play in determining biological responses to physical changes in the global environment.

3. During an El Niño, surface water in the eastern pacific is warmer than average and barometric pressures lower. During a La Niña, surface water in the eastern pacific is colder than average and barometric pressures higher. The effects of El Niño on global patterns of precipitation are summarized in figure 23.6. The effects of La Niña precipitation are generally the opposite over the same regions.

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4. Several examples of population effects of El Niño are presented in chapter 23. However, since rates of primary production and decomposition in terrestrial ecosystems are strongly influenced by precipitation and temperature, El Niño should affect rates of primary production and decomposition. You could test this hypothesis through long-term studies of primary production and decomposition through several El Niños and La Niñas.

5. Johnson's results suggest that the massive increases in fixed nitrogen cycling through the biosphere will select for less mutualistic mycorrhizal fungi. One way to test this idea would be to compare the performance of plants inoculated with mycorrhizal fungi from regions experiencing high rates of nitrogen deposition with the performance of plants inoculated with mycorrhizal fungi from regions experiencing low rates of nitrogen deposition.

6. Increased nitrogen availability should increase rates of primary production and decomposition in terrestrial environments and rates of primary production in marine environments. Increased nitrogen availability may strengthen phosphorus limitation of primary production in freshwater ecosystems. Again, as in the previous question, you could compare trends in primary production and decomposition in regions exposed to high versus low rates of nitrogen deposition.

7. The generalization that emerges from studies of diversity on islands and species area relationships on continents, is that fewer species live in smaller areas.

8. The intensity and extent of disturbance is much greater now than in any previous period in history. The long history of agriculture in the Amazon basin suggests that agriculture and high levels of biological diversity can coexist in the basin as long as the agricultural intensity is kept low to moderate.

9. The most compelling evidence that burning of fossil fuels are responsible for recent increases in atmospheric CO2 concentrations is the modern reduction of the 14C concentration in the modern atmosphere (See figure 23.23).

10. The main source of evidence that variation in atmospheric CO2 concentration is linked to variation in global temperatures is the record of ancient air preserved in the various ice caps around the globe. These records show a close tracking of CO2 and air temperature (see figure 23.20). Rapid climate change could lead to massive extinction of species, reduced crop production, which would threaten world food supplies, and impaired functioning of natural ecosystems.

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Answers to Critiquing the Evidence Critiquing the Evidence 1 1. New research tools increase the capacity of researchers to obtain information about ecological systems, which increases their capacity to test hypotheses.

Critiquing the Evidence 2 1. No, since both sample means are estimates of the population mean based on a random sample of the larger population, the two sample means are unlikely to be the same.

2. Yes, since larger sample sizes generally produce a better estimate of a population mean.

Critiquing the Evidence 3 1. The median.

2. A small number of very wealthy individuals in a population will distort the estimate of the income of the typical individual.

Critiquing the Evidence 4 1. The value of the range depends on the difference between a single pair of observations, that is, between the minimum and the maximum. The values of the standard deviation and the variance are determined by the difference between all of the observations and the sample mean.

2. Yes. For example, though average weights are exactly the same, all individuals in one population may have similar weights, while in another population, weight may differ a great deal from one individual to another.

Critiquing the Evidence 5 1. The ability to control most variables and isolate the ones of interest to the researcher.

2. Since ecology aims to understand the relationship between organisms and their natural environments, ecologists generally interpret the results of laboratory experiments within a natural context.

Critiquing the Evidence 6 1. Processing more samples than necessary requires time and other resources that could be used to conduct other research.

2. Flash flooding appears to have reduced the number of species in the disturbed reach.

Critiquing the Evidence 7 1. No. While a negative correlation between X and Y suggests the possibility of a causal relationship between the two variables, it does not demonstrate that changes in X cause changes in Y. In the case of the migratory redstarts, higher concentrations of C13 in the tissues of later migrants did not cause them to arrive later on the summer breeding grounds. The evidence, including lower body weight, suggests that it was the lower availability of food in the C4 plant dominated scrub habitats where these birds wintered (and assimilated higher levels of C13) that delayed their migration.

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Critiquing the Evidence 8 1. The main evolutionary implications are that natural selection on body size could lead to evolutionary change in body size in populations b and c but not in population a.

Critiquing the Evidence 9 1. young: variance/mean > 1; medium age: variance/mean = 1; older: variance/mean < 1 Critiquing the Evidence 10 1. By using a 0.05 significance level, we will reject correct hypotheses 5% of the time or, on average, 1 out of 20 times. In other words, we will correctly accept hypotheses 95% of the time and incorrectly reject them 5% of the time.

Critiquing the Evidence 11 1. Yes, since the critical value of χ2 for α = 0.01 and 2 degrees of freedom is 9.210 which is less than our calculated value of χ2 = 15.17.

2. The degrees of freedom would be 4: 5 − 1 = 4; critical value: χ2 = 9.488.

Critiquing the Evidence 12 1. No, statistical tests only allow us to make statements about the probability of a hypothesis being correct. In the case of species B, we can only say that the probability that it has a random distribution is less than 0.05.

2. The most direct way to strengthen the case for our conclusion that species B has a regular distribution would be to increase our sampling beyond the eleven 1 m2 sample plots to 50, 100, or more. Your conclusion will be strengthened if the results consistently indicate a regular distribution. However, it is possible that further study may lead you to reject your initial conclusion based on a smaller sample size.

Critiquing the Evidence 13 1. The reason for the fenced control plots is that the fence itself and the activity associated with its construction may have affected rodent densities. Without their carefully constructed control plots, Brown and his team could not have concluded that the increase in small granivore densities on the removal plots was the result of the absence of large granivore rodents.

Critiquing the Evidence 14 1. A larger sample provides a more precise estimate of the population mean.

2. Smaller samples, even though offering lower precision, may be preferable when studying an endangered population that could be compromised by too much sampling or when the costs in terms of time and money exceed the benefit gained by greater precision.

Critiquing the Evidence 15 1. The 95% confidence interval for the Gila River sample is: 56.2 mm ± 0.88 × 2.01 = 56.2 ± 1.77.

2. The value of t would be 2.11, since the degrees of freedom is 18 − 1 = 17.

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Critiquing the Evidence 16 1. Such a list would require a far greater investment in time, effort, and funds than any group of investigators or funding agency has been willing to commit.

2. Surveys of smaller groups of relatively well-known organisms are more manageable in terms of time and taxonomic expertise and therefore more likely to yield high quality results.

Critiquing the Evidence 17 1. Larger sample sizes improve the ability of a researcher to detect statistical differences between populations, since increasing sample size reduces the range of values included in the confidence interval. In other words, larger sample sizes provide a more precise estimate of the true population mean.

2. Increasing the level of confidence from 0.95 to 0.99 would increase the range of values included in the confidence interval.

Critiquing the Evidence 18 1. The outcome would have been the same, since the critical value of Student’s t for P < 0.01 and DF = 16, is 2.92, which is less than our calculated value of t, 3.480. Consequently, the probability that the population means are the same is less than 0.01.

Critiquing the Evidence 19 1. No, the t-test would not be appropriate in this case, since one of the assumptions of the t-test is that the two populations have equal variances.

Critiquing the Evidence 20 1. Interquartile ranges can represent variation around the median for a wide variety of distributions, many of which are highly asymmetrical.

2. Standard errors are calculated in a way that automatically produces symmetrical standard error bars under the assumption that the variable sampled has an underlying normal distribution, which is symmetrical.

Critiquing the Evidence 21 1. At this point, we cannot conclude that streams draining deciduous versus coniferous forest patches contain different amounts of detritus, since we have only sampled one stream associated with each type of forest. This issue is discussed at length in chapter 22.

Critiquing the Evidence 22 1. Since there is only one earth, our sample size for global-scale ecology is exactly one. The uniqueness of earth limits the kind of research that is possible and elevates the level of uncertainty around global-scale ecological theory. While other planets in the solar system provide some information that helps us understand planetary systems, they do not support a rich biosphere. Therefore global ecologists draw heavily on earth history and computer-based models to understand global-scale phenomena.

Critiquing the Evidence 23 1. It is generally necessary to narrow a literature search when working on a topic in which there is a high level of research activity. For instance, searching with a single key word relating to

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a core area of ecology, such as ―climate‖ or ―global warming,‖ will yield thousands of references. Narrowing a search will result in a smaller, more manageable list that can be reviewed critically to identify the references that merit further reading.

2. Broadening a literature search is important when working on a subject in which there is has been little research. When working on topics with a small pool of published papers, broader searches will identify more of the relevant references.

Answers to Concept Review Questions Chapter 1 Concept 1.1 Review Answers 1. The level of organization studied by an ecologist largely determines the types of questions addressed as well as the design of studies used to answer those questions.

2. Levels of ecological organization do not exist in isolation. The structure and function of each level is determined by interactions at lower levels of organization and influenced by interactions at higher levels of organization. Studies aimed at one level of organization often need to assess the influences derived from many other levels. For example, predators and parasites may have significant influence on zebra population size -and variation in physical environment due to global climate change (such as precipitation) will likely affect the availability of resources for the zebras, and therefore, their general health and reproductive success.

Concept 1.2 Review Answers 1. The three types of ecological research include observation, experimentation, and modeling.

Observations can extend over space and time, and include the collection of data in unmanipulated settings (in the field, or using specimens collected in the field). This type of research can be entirely descriptive, or may be focused on testing a specific hypothesis.

Experimentation involves the manipulation of variables of interest under controlled conditions in order to test a specific hypothesis. This type of research can take place in the field or in more controlled settings such as a greenhouse or lab. Field experiments come closer to measuring real-life conditions, but may include variables that are difficult or impossible to control. Ex situ (away from the natural location) experimentation is generally easier to control, but may over-simplify real-life conditions. Modeling involves the creation and analysis of representations of data and may be used to simulate natural systems and test scenarios that are difficult or impossible to manipulate in real life. This type of research may be conceptual and descriptive, or quantitative and designed to test specific hypotheses.

Observational studies can stimulate experimental studies. Experimentation may raise more questions and suggest the need for additional observation. Models can be used to describe, summarize, and/or understand data collected through observation or experimentation. Models may represent a new hypothesis and/or make predictions that can be tested with future observations and experimentation.

2. New tools such as cranes, drones, and special camera equipment allow ecologists to make observations at times and locations that are otherwise difficult to reach. Recordings and sound equipment can record and analyze sound in locations and conditions that were previously unreachable. New technologies such as stable isotope analysis and genetic technologies can identify small pieces or traces of organisms and reveal ecological Copyright © McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education.

interactions that are otherwise invisible. Computer technology allows ecologists to analyze very large data sets and run extremely complex calculations and simulations that were previously impossible. Citizen science helps to obtain very large samples over wider geographic areas and time scales than would be otherwise possible.

3. Many of the most important changes in ecological systems occur over long periods of time and large spatial scales (such as plant adaptation in Appalachian forests, or changes in bird distribution and migration patterns in response to global change). To fully understand these systems and processes, it is important to be able to collect data from the past (from fossils, museum specimens, ice-cores, tree-rings, historical records, etc.), and use models to make predictions about the future.

Chapter 2 Concept 2.1 Review Answers 1. There would be little or no seasonality in either temperature or precipitation.

2. The sun is directly overhead at 23.5° N latitude on June 21, the beginning of summer in the Northern Hemisphere, which results in cloud formation and precipitation at that latitude.

Concept 2.2 Review Answer 1. The development of an organic horizon is limited in deserts as a result of low production of organic matter by plants and removal of organic matter from the soil surface by wind and water (during infrequent, intense rainstorms).

Concept 2.3 Review Answers 1. Along their slopes, high mountains include a broad range of environments that can support a high diversity of organisms.

2. Greater rainfall, higher average temperatures, and higher levels of biological activity all contribute to higher rates of nutrient depletion in tropical rain forest soils.

Chapter 3 Concept 3.1 Review Answers 1. Since glaciers and polar ice are melting with increasing global temperatures, the amount of the earth’s water stored in the oceans will gradually increase, resulting in a rise in sea level.

2. Storage reservoirs increase river water turnover time.

Concept 3.2 Review Answers 1. Zebra mussels have increased the availability of phosphorus and nitrogen which often limit phytoplankton growth.

2. Corals are very sensitive to high temperatures and may suffer substantial mortality if ocean surface temperatures increase by just a few degrees.

3. Organisms that inhabit estuaries and salt marshes must live in conditions involving highly variable temperatures, salinities, oxygen concentrations, and water flows. Consequently, physiologically sensitive individuals suffer higher mortality and lower reproductive rates.

Chapter 4 Concept 4.1 Review Answers 1. Differences in growth within clones of P. glandulosa grown at different elevations could not be the result of genetic differences, since the cloned plants were genetically identical.

2. If alpine, mid-elevation, and lowland populations of Potentilla glandulosa were not different

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genetically, the researchers would not have found differences among ecotypes in height or number of flowers in the common gardens.

3. One of the major implications of widespread genetic variation in natural populations is that there is great potential for evolution by natural selection in most natural populations.

Concept 4.2 Review Answers 1. Genetic drift is more likely in small populations, since accidents and other random factors that cause mortality or alter mating patterns affect a larger proportion of individuals, and the genes they carry, in small populations.

2. Selective mating, which can change gene frequencies in populations, disrupts HardyWeinberg equilibrium. In other words, selective mating is a source of evolutionary change in populations.

3. Immigration into a small population has the potential to sustain the genetic variation, which genetic drift generally reduces.

Concept 4.3 Review Answers 1. No. The population may be subject to strong stabilizing selection.

2. Rapid, human-caused environmental change can outpace a population’s capacity to adapt to the change through a process such as directional selection.

Concept 4.4 Review Answers 1. No; such a trait cannot evolve, since none of the variation in the trait is the result of genetic differences among individuals, and therefore advantageous variations in the trait cannot be inherited.

2. Beak length must have varied among individual soapberry bugs.

3. Mating between Geospiza fortis and G. Magnirostris could introduce alleles for larger beak size into the G. fortis population thereby establishing greater genetic variation on which natural selection might act.

Concept 4.5 Review Answers 1. Higher levels of genetic diversity within a population increases the probability that the population will persist in nature, especially in the face of environmental challenges, such as infectious disease.

2. Because the females were less choosy on all of the islands, we know that this trait (choosiness) was lost through genetic drift; that is, it was a random occurrence, not driven by natural selection from the parasitic fly.

Chapter 5 Concept 5.1 Review Answers 1. The temperature of streams varies throughout the day due to sun exposure. Increased sun exposure will cause the water temperature to rise, and decreased sun exposure will cause the temperature to fall. Stream-side vegetation can shade the water, and impact the amount of sun exposure throughout the day. Streams with dense canopies will remain shaded throughout the day, keeping the water cooler. The temperature of water in streams with intermediate canopies will vary more, depending on the variation of sun and shade at various time in the day. The water temperature of streams with little or no canopy will warm more dramatically, but vary less, than streams with intermediate canopies.

2. Evaporation of a very small mass of water can cool a very large mass of air or living matter.

3. While the aboveground parts of plants are subjected to the full variation in temperature in a particular climate, roots, especially deep roots, are exposed to little temperature variation.

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Concept 5.2 Review Answers 1. The scatter of points in figure 5.7 would move directly upward, with half the points above the horizontal axis and half below, indicating higher fitness at 20°C but unchanged fitness at 40°C. 2. Your team would conclude that the experimental results failed to support the principle of allocation, since increased fitness at 20°C was not accompanied by reduced fitness at 40°C. Concept 5.3 Review Answers 1. Impaired acetylcholinesterase may interfere with the functioning of neurons that coordinate swimming movements and orientation.

2. The experimental plants were clones grown from cuttings and were therefore genetically identical.

Concept 5.4 Review Answers 1. By reducing light absorption, highly reflective leaves would unnecessarily reduce leaf heating and rate of photosynthesis during the cool season.

2. Yes. Consider thermoregulation by Sceloporus lizards (see fig. 5.19) and clear-winged grasshoppers (see fig. 5.21).

3. Small fish have a larger surface area exposed to the environment compared to their mass and would have to generate far more metabolic heat to maintain swimming muscles at temperatures above that of the surrounding water.

4. All three organisms show a thermal optimum. However, Entomophaga grows at a high rate in a greater range of temperatures compared to the microbes.

Concept 5.5 Review Answers 1. Hummingbirds may be more susceptible to predators while in torpor.

2. Water availability and food production are much more seasonal in tropical dry forests.

Chapter 6 Concept 6.1 Review Answers 1. The two curves are similar because the amount of pressure exerted by a gas, in this case water vapor, is directly proportional to its density.

2. Since water flows from pure water to seawater across a semi-permeable membrane and water flows from regions of high free energy to regions of low free energy, pure water must have a higher free energy content than seawater.

3. Since all natural waters, even rainwater, contains some dissolved substances, their water potentials are less than that of pure water (= 0) and therefore negative.

Concept 6.2 Review Answers 1. Because cuticular hydrocarbons require energy for their synthesis, Cicindela oregona in wetter climates that maintained lower concentrations of cuticular hydrocarbons could potentially allocate more energy to reproduction.

2. The death of some branches reduces water use and increases the water available to the surviving branches.

3. Generally, water loss rates increase as body temperature rises. In addition, temperature and water regulation are directly linked in species—such a cicadas, humans, and horses—that use evaporative cooling to regulate body temperature.

Concept 6.3 Review Answers 1. Isosmotic marine invertebrates, whose body fluids contain equal concentrations of salts and water as the external environment, expend less energy in osmoregulation, since the amount

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of energy that an aquatic organism expends in osmoregulation is proportional to the difference in osmotic pressure between the organism and the environment.

2. Low internal salt concentrations reduce the amount of energy expended for osmoregulation.

Chapter 7 Concept 7.1 Review Answers 1. C3 plants do best under moist conditions. Under hot, dry conditions C3 plants close stomata as a means of conserving water, cutting off the supply of CO2 for photosynthesis. Reduced CO2 concentrations also lead to increased photorespiration, which further reduces energy supplies.

2. C4 and CAM photosynthesis both fix and store CO2 in organic acids containing four carbon atoms and both photosynthetic pathways separate carbon fixation from the light-dependent reactions of photosynthesis. However, C4 plants separate these reactions in space, with carbon fixation taking place in the mesophyll cells and the light-dependent reactions occurring in the bundle sheath cells, while CAM plants separate the reactions in time (night versus day).

3. Rising CO2 levels have been accompanied by rising temperatures and may lead to increased drought in the future, factors favorable to C4 plants.

Concept 7.2 Review Answers 1. The chemical energy of the products must be less than that of the reactants.

Concept 7.3 Review Answers 1. Pumas and their herbivore prey are very similar in terms of elemental composition, for example both predator and prey have low C:N and C:P ratios. In contrast, a deer must eat much more plant material to satisfy its nutritional need for nitrogen and phosphorus, since plants have high C:N and high C:P ratios.

2. A detritivore must consume even greater amounts of its main food compared to a herbivore to satisfy its nutritional needs for elements, such as nitrogen, since dead plant material is even lower in nutrient content than living plant tissues, for example, higher C:N ratios.

3. A mutant within a population of a non-aposematic, nonpoisonous species that showed, for example, a single bright orange spot might have a lower probability of being attacked by a would be predator. Even a slightly higher probability of survival, for example 1%, could lead to the mutation increasing in frequency in the population. As successive chance mutations resulted in individuals closer in appearance to a noxious species in the environment, they too would experience higher survival and the mutations would increase in frequency in the population. Gradually the Batesian mimic would converge on the form of the noxious species.

Concept 7.4 Review Answers 1. Some consumers ignore a potential food until it exceeds some threshold density, and may require a learning period to fully develop searching and handling skills for a particular food item before they can feed on it efficiently.

2. The adaptations that enable them to photosynthesize at relatively low levels of irradiance can be damaged by high irradiance.

3. Even under ideal conditions, organisms as different as wolves, moose, and the plants eaten by moose take in energy at a limited rate.

Concept 7.5 Review Answers 1. When adding the new prey item increases the predator’s rate of energy intake.

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2. The bluegills in the study almost entirely ignored the most abundant prey in the environment, those approximately 1 mm in length.

3. Including several replicates of each growing condition for each species provided a basis for calculating the mean and variance in response for each species and testing the statistical significance of the results.

Chapter 8 Concept 8.1 Review Answers 1. The influence of prey color on vulnerability to predators is strongly influenced by the background against which the predator views the prey.

2. The observed increase in colorfulness among male guppies in the absence of effective predators suggests that colorful males have some selective advantage, probably related to how female guppies choose their mates.

3. One advantage to females mating with colorful males is that it increases the chances of their giving birth to colorful sons who will be attractive to prospective mates.

Concept 8.2 Review Answers 1. Male scorpionflies fight over dead arthropods and even steal arthropods from spider webs where they may be trapped.

2. Males guarding large and medium sized dead insects have greater mating success than males guarding small dead insects or salivary masses.

3. The largest male scorpionflies, and presumably the best at defending resources, are able to maintain possession of the highest quality nuptial offerings.

Concept 8.3 Review Answers 1. To demonstrate nonrandom mating and sexual selection in plants, it is necessary to show maternal control over the fertilization process, competition among pollen, or a combination of both. In experiments with a mix of pollen donors, certain donors would sire a greater proportion of offspring, and those offspring would have a greater chance of survival (larger seeds and greater access to maternal resources). There must also be evidence that these traits are heritable in order to demonstrate that nonrandom mating could result in sexual selection.

2. If mating in these populations was truly random, Marshall and Fuller’s data would show that each potential pollen donor would sire a relatively equal proportion of offspring.

Additionally, the seeds sired by each donor would be the same weight and would be randomly distributed in the fruit.

Concept 8.4 Review Answers 1. Helpers and their half siblings would be related genetically by an average of 25%.

2. The helper would derive more benefit through kin selection by helping raise a full sibling, since, on average, the genetic similarity between a helper and a full sibling is twice as high as that between a helper and a half sibling.

3. This pattern suggests that male lions avoid the risk of helping without gaining in inclusive fitness.

Concept 8.5 Review Answers 1. A hymenopteran queen mating with several males would reduce the relatedness of workers.

Reduced relatedness among workers would decrease the potential of kin selection to account for evolution of eusociality in the Hymenoptera.

2. The two major ecological challenges are the need to excavate and maintain large burrow systems and the need for defense.

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3. The colonies of both leafcutter ants and naked mole rats include soldier castes, specialized for defense.

Chapter 9 Concept 9.1 Review Answers 1. A species may shift its geographical distribution with climate change; it may adapt to the new environmental conditions; or do both. Large and rapid climate change may lead to extinction.

2. A combination of physical and biological factors may restrict a distribution more than would physical factors alone, since less than optimal physical conditions may make a species more vulnerable to attack by pathogens, parasites, or predators, or less effective in competition with other ecologically similar species.

Concept 9.2 Review Answers 1. No. Relative sizes and dispersal abilities of species must be taken into account when distinguishing between large and small scale. For instance, mammals and birds of the same size use the environment on significantly different scales, as do mice and elephants.

2. To test the hypothesis, selectively remove, or kill, individual shrubs and determine if the root systems of surrounding creosote bushes grow into the vacated area.

3. The measurements demonstrated that the number of colonies in the study area was not limited by availability of suitable nest trees and that clumped or regular distributions would not be the result of an underlying clumped or regular distribution of potential nest sites.

Concept 9.3 Review Answers 1. Some factors favoring winter aggregation by crows, and other birds, include protection from predators, more effective foraging in flocks, and pairing of males and females for the spring nesting season.

2. Food is generally abundant along river valleys.

3. The observation that pines (Pinus cembroides in Arizona and Pinus pungens in Tennessee) inhabit the driest sites in both mountain ranges suggests that pines are relatively drought tolerant.

Concept 9.4 Review Answers 1. By restricting his analysis to herbivorous mammals, Damuth controlled for the potential influence of feeding ecology and evolutionary history on factors that affect density.

2. Birds may live at lower densities because their food is less abundant, because they require more food to support their activity and metabolic rate, or both.

Chapter 10 Concept 10.1 Review Answers 1. The documented dispersal rate of Eurasian collared doves is much higher than that shown by hemlock and maple trees.

2. Since, according to Müller’s colonization cycle, stream insects need to compensate for downstream movements during drift, the predominant direction of flight by reproductive adult stream insects should be upstream.

Concept 10.2 Review Answers 1. The populations of both butterflies increase in size with increased habitat area. The Glanville fritillary has much larger population sizes for a given meadow area compared to the Rocky Mountain Parnassian.

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2. Joining a larger population in a larger meadow increases the chances of increased genetic variability in future generations and reduces the chances of joining a subpopulation on its way to extinction.

3. While fire suppression by forest managers contributes to the decline of a Rocky Mountain Parnassian butterfly metapopulation, traditional farming appears to contribute to the growth of the lesser kestrel metapopulation of the Ebro River valley.

Concept 10.3 Review Answers 1. Substantial emigration would generally result in overestimates of death rates, while substantial immigration would result in underestimates of death rates.

2. Yes, cottonwood trees must have type III survivorship.

3. Infants, children, young adults, middle-aged adults and the elderly would all die at equal rates.

Concept 10.4 Review Answers 1. Yes, many populations, such as the large cactus finches of Genovesa Island, live in environments that are only intermittently suitable for reproduction (see fig. 10.21).

2. Yes, there was a 10-year gap in reproduction, shown by the absence of 60-year-old trees in the age distribution.

Concept 10.5 Review Answers 1. The population of white oaks represented by figure 10.19 is the only one that is likely to have a stable age distribution.

2. Values of R0 greater than 1.0 indicate a growing population.

3. The population could be sustained over the long term, if it is part of a metapopulation and receives immigrant turtles from other nearby habitats.

Chapter 11 Concept 11.1 Review Answers 1. Bennett’s assumption was that the rate of pollen deposition is proportional to the size of the Scots pine population around a lake.

2. Exotic species introduced from their native geographic region to a new environment that is suitable physically may encounter fewer competitors in the new environment and are generally introduced without most of the pathogens, predators, and parasites that negatively impact their populations in the native region.

3. Guppy population growth would be best modeled as exponential growth, while African annual killifish population growth would be best represented by geometric growth.

Concept 11.2 Review Answers 1. Population growth is initially rapid, since barnacles colonize the open substrate and N is much less than K. Population growth begins to slow near week 2 as space approaches full occupation and N almost equals K. After 4 weeks population density declines, perhaps because N has exceeded K, as barnacles compete with each other for exclusive use of limited space.

2. At low population density, when theoretically, critical resources, such as food and space, are abundant and pressures from predators and pathogens are low, the per capita rate of increase, r, is approximately rmax, since N/K, environmental resistance, is near zero and 1-N/K is approximately 1.

3. Since logistic population growth is highest at a population size of K/2, and lower at smaller population sizes, reducing the population below K/2 would slow the recovery of the

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population from the effects of harvesting.

Concept 11.3 Review Answers 1. Given the reproductive potential of all populations, if they were not under some form of control we would see many species attain population sizes of plague proportions.

2. The amount of rainfall available to stimulate plant growth appears to set the carrying capacity.

3. While the population of medium ground finches on Daphne Major Island increases during years of higher rainfall, long-term, persistent increases in moisture could have a negative impact on medium ground finch populations. For instance, long-term increases in rainfall could increase populations of mosquitoes that transmit bird pathogens or could change the composition of plant community in ways that reduce the production of suitable food.

Chapter 12 Concept 12.1 Review Answers 1. By including plants from five different regions on three continents, Westoby, Leishman, and Lord increased their chances of discovering patterns of general importance. If they had worked within a single region, they could not be sure that the patterns would hold for other regions.

2. The greenhouse environment allowed Jacobsson and Eriksson to control significant environmental factors such as soil type, moisture availability, and temperature. These controls ensured that differences in seedling size were mainly the result of differences in seed size and not the result of differences in the environments in which the seeds germinated.

3. Because of the relationship between egg size and gene flow in darter populations (see fig.

12.5) you should observe more genetic differences along the length of a river system among smaller darter species.

Concept 12.2 Review Answers 1. Because GSI is calculated as ovary weight divided by body weight, GSI is reproductive allocation expressed as a proportion of body weight. Converting these proportions to percentages, we see that the allocation of the rougheye rockfish to reproduction is 2% of its body weight compared to 65% of body weight by the northern anchovy.

2. The main focus of the study by Bertschy and Fox was on variation in life history among several populations of a single species, the pumpkinseed sunfish, while Gunderson’s study contrasts life histories across many species.

3. By restricting their study to lakes without major inflows or out-flows, Bertschy and Fox could remove the potential effects of immigration and emigration on their populations. Such movements could obscure the effects of natural selection within the lakes for particular life history characteristics.

Concept 12.3 Review Answers 1. Yes. Though the concept of r and K selection has been replaced by more inclusive and quantified ideas, such as Charnov’s life history cube (see fig. 12.24), it stimulated the thinking, discussions, and research that eventually led to more sophisticated concepts, and the process continues.

2. The plant species most closely matches Grime’s ruderal life history of low stress–high disturbance and Winemiller and Rose’s periodic life history.

Chapter 13

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Concept 13.1 Review Answers 1. Since natural densities of Porcellio scaber sometimes exceed 2,000 per square meter, food limitation might not occur until such densities are approached.

2. While food supplementation did not affect survival, attributes such a reproductive rate, growth rate, etc., may have been affected by food supplementation.

Concept 13.2 Review Answers 1. One of the most fundamental assumptions of the competitive exclusion principle is that resources are available in limited supplies.

2. Yes, at least occasionally. For instance, the medium ground finches, Geospiza fortis, on Daphne Major have periods of very strong competition for limited food periodically—during droughts.

Concept 13.3 Review Answers 1. This contrast in the time to competitive exclusion suggests that food availability played a key role in competition between the two species and that reducing food supplies increased the intensity of interspecific competition.

2. No, reaching such a broad conclusion based on mathematical models and laboratory experiments would be going beyond the proper role for model systems, which are best used to suggest hypotheses and guide experimentation on natural populations.

3. Yes, a predator that kept the population densities of both species below the lower isocline of zero growth, where population growth of both species is positive, would enable coexistence of the two species.

Concept 13.4 Review Answers 1. Even though there were a few healthy G. sylvestre plants remaining in the acidic soil boxes at the end of 6 years, G. saxtille is the better competitor in these soils and likely would eventually exclude G. sylvestre given enough time. The delayed exclusion was probably the result of the slow growth of both species on acidic soils. The results of the experiment suggest that interspecific competition restricts the realized niche of each Galium species to a narrower range of soil type than they are actually able to grow in without competition.

Specifically, they are restricted to the soil type in which they are the superior competitor.

2. The difference in response by small granivore rodent and insectivorous rodent populations suggests that the limiting resource over which small and large granivore rodents compete is seeds, which is critical for them but not for insectivorous rodents.

3. By reproducing the main results of the first experiment, the second experiment greatly strengthens the case for competition between large and small granivore rodents at their study site.

Chapter 14 Concept 14.1 Review Answers 1. They did not reach a firm conclusion regarding the effect of Helicopsyche on its food supply based on the first experiment because there are many other benthic invertebrates living in their study stream that might be depleting algal populations. In addition, changes in physical conditions, such as variation in stream flow, during the first experiment could have caused the fluctuation in both algal and Helicopsyche populations.

2. To test for the combined effects of birds and bats on populations of foliage living arthropods you could leave the exclusion nets on day and night.

Concept 14.2 Review Answers

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1. Lynx, which are specialized for preying on snowshoe hares, are only one of many predators that feed on snowshoe hares. In addition, snowshoe hare densities decline in response to the hare’s reducing their own food supplies during times of high population density.

2. Because organisms are subject to such a large number of environmental forces, it is likely that most ecological phenomena result from the effects of a combination of environmental variables, often interacting in complex ways, rather than from a single factor.

3. Mathematical models give the researcher total control of the predator-prey system but are abstractions that can include ecologically unrealistic characteristics. Laboratory models, because they involve living predators and prey, can have greater correspondence to predatorprey systems in nature. However, laboratory models are very difficult to sustain over the long term.

Concept 14.3 Review Answers 1. Several factors make coexistence between predators and prey less likely in a laboratory setting compared to nature. Chief among these factors are the generally smaller scale of laboratory compared to natural systems and the lower spatial complexity of laboratory settings.

2. Individuals emerging at the same time as most of the rest of the population would have a much lower probability of being eaten by predators.

Concept 14.4 Review Answers 1. There is no potential for interference among predators, when there is a single predator in the environment. Therefore the prey-dependent and ratio-dependent models of functional response fit the data equally well. The potential for interference among predators increases as predator numbers increase. Prey-dependent models of functional response should be most accurate where predator densities are very low.

2. The factors that make the situation on Isle Royale nearly ideal for studying wolf-moose interactions are that in contrast to other populations, the wolves on Isle Royal feed almost exclusively (90%) on moose and there is almost no immigration or emigration by either wolves or moose.

Concept 14.5 Review Answers 1. Moore did ―blind‖ observations to avoid any potential for observer bias based on expectations of how infection may affect behavior.

2. The laboratory experiments demonstrated that infected Armadillidium behave in a way that should make them more vulnerable to starling predation in nature. The field observations verified that starlings feed infected Armadillidium at a higher rate than one would predict based on their frequency in the population.

Chapter 15 Concept 15.1 Review Answers 1. Johnson always mixed sterilized and unsterilized soils from the two study areas when preparing her inocula to control for the possibility that some nonbiological factor, such as trace nutrients in one of the two study areas, might have a measurable effect on plant performance.

2. Johnson used a sterilized mixture of soils from the fertilized and unfertilized study areas for her controls to guard against the possibility that the soils themselves, without mycorrhizal fungi, might affect plant performance.

3. It may have been that plants with ants are visited by seed predators less often for reasons

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other than the presence of ants. If so, demonstrating that plants without ants experience greater seed predation may have simply reflected a low overlap in the distributions of ants and seed predators.

Concept 15.2 Review Answers 1. The expulsion of zooxanthellae by corals placed in the dark is further indication that the coral is in control of their mutualistic relationship with zooxanthellae.

2. Corals expelling their zooxanthellae in the dark suggests that, in the absence of photosynthesis, there is a net cost to the presence of zooxanthellae in coral tissues.

Concept 15.3 Review Answers 1. Because of the long-standing mutualism between ants and Helianthella quinquenervis, Keller’s theory, and Inouye and Taylor’s experimental results, would predict that the mutant plants would have lower fitness.

2. The mutant, nonmutualistic Helianthella quinquenervis could be expected to replace the mutualistic plants that produce extrafloral nectaries when, or where, the fitness of the mutant, nonmutualistic plants exceeds that of the mutualistic plants.

Chapter 16 Concept 16.1 Review Answers 1. These data suggest that most species are moderately abundant, and that it is less common for species to be very abundant or very rare.

2. Smaller samples are more likely to detect the very abundant and moderately abundant species, and less likely to detect the very rare species. An increase in sampling will increase the likelihood of detecting rare species and revealing the characteristic lognormal distribution.

Concept 16.2 Review Answers 1. Generally only a minority of species is tolerant of any given pollutant, which reduces species richness, and of those tolerant, only a few are abundant, which reduces species evenness.

2. The Shannon-Wiener diversity of community c (H = 1.514) is lower compared to community b and higher than community a.

Concept 16.3 Review Answers 1. Tilman’s discovery that Asterionella and Cyclotella exclude each other under certain conditions but coexist under other conditions does not violate the competitive exclusion principle, since he found that they have different nutrient requirements. In terms of the competitive exclusion principle, Asterionella and Cyclotella have different niches.

2. Increasing nutrient availability by fertilizing reduces the number of potentially limiting nutrients, which is one indicator of environmental complexity. Eventually when all nutrients but one are abundant, the plant species most effective at competing for that nutrient will predominate in the community.

3. Since the fish species inhabiting small isolated patches of coral reef use different vertical zones on the reef face, the diversity of fish should increase with increasing reef height, in a manner analogous to the positive relationship between foliage height diversity and bird species diversity.

Concept 16.4 Review Answers 1. Imposing fire protection on forests that have had fire as a natural part of their environment for long periods could lead to reduced plant diversity by decreasing the variety of habitats across the landscape. In the absence of periodic fires the landscape could eventually be

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dominated by mature forest. In contrast, allowing periodic fires to burn would create a patchwork of plant communities of various successional stages (see chapter 20), from young to mature, which would sustain higher plant diversity across the landscape.

2. Often human sources of disturbance to natural communities are of high intensity.

3. Theoretically, human disturbance could sustain higher levels of species diversity, if the levels of human disturbance did not exceed moderate levels of intensity and frequency.

Chapter 17 Concept 17.1 Review Answers 1. Including only strong linkages in a food web makes the main feeding relationships more apparent and helps identify the main routes by which predators impact prey populations.

2. Tscharntke simplified the food web primarily by distinguishing between weak and strong trophic linkages in his representation of blue tits feeding on the insects living on the wetland reed Phragmites australis.

3. Another way in which Tscharntke simplified his study was to focus on a trophic interaction involving a single bird species and the insects living on a single plant species. In other words, he focused on one part of the much larger and much more complex wetland-wide food web that includes many species of birds, plants, insects, and other organisms.

Concept 17.2 Review Answers 1. Both competition and apparent competition involve negative effects between species.

2. The negative effects resulting from competition are the result of direct interactions between species, while in apparent competition they occur through an intermediary species.

3. If the affect of Brassica nigra on Nassella pulchra was the result of direct competition, with small herbivorous mammals playing no significant role, the densities of N. pulchra seedlings and adult plants would increase away from B. nigra patches both where small herbivorous mammal were present and where they were absent.

Concept 17.3 Review Answers 1. No, while the pattern described by Paine was consistent with the predation hypothesis, it does not directly demonstrate that predators influence the number of species in communities. To confirm his hypothesis, he needed an experimental test.

2. The major limitation of Paine’s first removal experiment, involving Pisaster was that his control and removal plots were not replicated.

3. Littorina prefers to feed on Enteromorpha, an algal species that can outcompete the alga Chondrus. Consequently, in the absence of Littorina, Enteromorpha competitively excludes Chondrus. However, where it is present in high densities, Littorina grazes down the Enteromorpha population, releasing Chondrus from competition with Enteromorpha.

4. Since Littorina avoids feeding on the competitively dominant algae Fucus and Ascophyllum and feeds on their competitors instead, Littorina accelerates the competitive exclusion of these other algal species, reducing algal diversity on emergent substrata in the process.

Concept 17.4 Review Answers 1. Natural loss or addition of the cleaner fish, Labroides dimidiatus, may have been the result of factors that also influence the presence or absence of other fish species. If so, changes in fish species richness would be correlated with the presence or absence of the cleaner fish but not caused by the cleaner fish’s presence or absence.

2. Pollinators may act as keystone species in many communities. Therefore their loss may threaten the existence of many other species.

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Chapter 18 Concept 18.1 Review Answers 1. A likely reason that precipitation alone was sufficient to account for most of the variation in grassland net primary production across central North America is that warm temperatures occur during the growing season at all of the sites included in the study by Sala et al. (1988).

In other words, actual evapotranspiration at these study sites would be determined mainly by precipitation.

2. The desert dune ecosystem and the arctic and alpine tundra ecosystems all show low actual evapotranspiration and low net primary production.

3. Actual evapotranspiration would increase substantially in the desert dune ecosystem, since it is a hot desert. However, AET might not increase a great deal in the arctic and alpine tundra ecosystems, since they are both cold, which limits evaporation.

Concept 18.2 Review Answers 1. The most likely explanation is that nitrogen is not limiting phytoplankton biomass in the study lake, while phosphorus is highly limiting.

2. The most likely explanation is that phytoplankton biomass in the study lake is not controlled by nitrogen and phosphorus concentrations.

Concept 18.3 Review Answers 1. The research group manipulated the species richness component of species diversity. Species evenness might also influence rates of primary production.

2. The positive effect of legumes, which fix atmospheric nitrogen and can increase nitrogen availability in soils, suggests that nitrogen availability is one of the factors limiting primary production in the experimental plots.

3. Other potential contributors to variation among study plots include differences in soil structure and differences in availability of soil nutrients among plots.

Concept 18.4 Review Answers 1. A negative correlation between zooplankton size and phytoplankton primary production means that lakes with larger zooplankton support lower phytoplankton primary production.

2. Assuming that increased fishing pressure reduces the large-mouth bass population significantly, water clarity should decrease as fishing pressure on the largemouth bass population increases.

3. A major reason it is more difficult to get evidence of a trophic cascade in a terrestrial ecosystem such as the Serengeti is that it would be much more difficult to conduct an experiment on spatial scale large enough to include populations of lions and wildebeest.

Another reason is that few terrestrial environments still support populations of large predators and large native herbivores.

Concept 18.5 Review Answers 1. Because energy losses between trophic levels reduce biomass and population sizes at higher trophic levels, at some point energy availability will be too small to support a viable population size of consumers at a trophic level higher than already exists in the ecosystem.

2. Yes, equal biomass but differing production is possible, where mortality due to predation sustains a lower biomass of a population with higher secondary production.

3. Secondary production should change in such a stream in response to reduced inputs of detritus. Specifically, secondary production in the stream will likely decline with reduced inputs of detritus.

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Chapter 19 Concept 19.1 Review Answers 1. The oceans are acting as a phosphorus sink, since the inputs of phosphorus from the Atmosphere exceed the flux of phosphorus to the atmospheric pool. In additions, inputs from runoff, with no clear compensating flux from the oceans to land add to the role of the oceans as a phosphorus sink.

2. On land the rate of nitrogen fixation (140 x 1012 g N per year) exceeds the rate of denitrification (130 x 1012 g N per year). Meanwhile, in the oceans nitrogen fixation (30 x 1012 g N per year) is far less than denitrification (110 x 1012 g N per year).

3. Replacing tropical forests with less productive cattle pastures adds CO2 to the atmosphere as the cut forest vegetation decomposes and/or burns and reduces the amount of tropical forest available to act as a carbon sink.

Concept 19.2 Review Answers 1. Ecologists study decomposition because it is a key ecosystem process that is integral to nutrient cycling. Understanding controls on rates of decomposition is fundamental to understanding how ecosystems work and is intimately related to ecosystem and community properties ranging from rates of primary production to species diversity.

2. Ecosystem ecologists are exploring the influences of atmospheric CO2 concentrations on leaf lignin content because of the potential effects of elevated CO2 on decomposition and nutrient cycling.

3. Decomposition rates increased both in response to increased nitrate concentrations (fig.

19.12) and to increased phosphorus concentrations (fig. 19.13). However, while rates of leaf decomposition leveled off at higher phosphorus concentrations, decomposition rates continued to rise in response to increased nitrate levels.

Concept 19.3 Review Answers 1. Reasoning from the results of McNaughton, Ruess, and Seagle in the Serengeti (fig. 19.19), the removal of bison from the Great Plains likely reduced rates of decomposition and nutrient cycling substantially, possibly reducing rates of primary production.

2. Vertebrate consumers have a higher phosphorus requirement to maintain their phosphorusrich skeleton compared to invertebrates. Vertebrate P content is over twice that of invertebrates so they have much lower N:P ratios and have lower N:P excretion ratios.

3. Occupation of a site by one of these nitrogen-fixing species would increase the nitrogen content of soils over time. So, even with complete removal of these exotic species, the legacy of greater nitrogen content in the site’s soils might alter the suitability of the site for native species and change the potential diversity of native plants that could coexist on the site, at least for the short term (see figs. 16.15 and 16.16).

Concept 19.4 Review Answers 1. The large scale of their experiment limited the experiment to a single control stream basin and a single treatment stream basin.

2. Both studies show that vegetation plays a key role in regulating nutrient retention in forest ecosystems. Likens and Bormann restricted the development of vegetation using herbicides after clear-cutting the forest. This prevented uptake of nitrogen by new understory and forest growth and increased nitrogen loss, whereas the rapid development of vegetation following the fires in Yellowstone decreased nitrogen losses from the system.

3. Meyer and Likens’ finding, that most phosphorus losses from Bear Brook occurred during

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floods, suggests that in the absence of flooding, streams and rivers could retain more phosphorus and, potentially, other nutrients as well.

Chapter 20 Concept 20.1 Review Answers 1. Natural processes of succession generally occur over very long periods of time (frequently more than a single human lifetime), so our understanding of this process is likely to change based on the amount of time we have actually been able to observe. Classic studies of succession used chronosequences -a set of study sites that share many attributes but represent different ages since disturbance in an attempt to infer long-term changes. One problem with chronosequence-based studies is that is difficult or impossible to control for variables other than age that might contribute to observed differences in community structures between sites.

Many recent studies have revisited classic chronosequences (such as Glacier Bay), and followed up with empirical observations. These studies have generally not supported the classic interpretation that succession normally follows a predictable pattern, and instead suggest that species composition is often dependent on more stochastic events, such as which species happens to reach a location first, or the frequency and strength of disturbance events.

2. The primary reasons for differences in the rates of succession in forest and rocky intertidal communities are differences in the rates of dispersal and growth of the organisms making up each of these communities.

Concept 20.2 Review Answers 1. The changes in soil properties that the researchers documented demonstrate that succession involves more than changes in the diversity and composition of species. Terrestrial succession also involves changes in key ecosystem properties, including the properties of soils.

2. Equal levels of nitrogen input and output in the stream reaches studied by Nancy Grimm would indicate that the reach was neither storing (retaining) nor exporting (losing) nitrogen.

3. The chronosequence on Hawaiian lava flows suggests that the typical shorter term studies of succession do not provide insights into changes that occur on geological time scales.

Concept 20.3 Review Answers 1. Disturbance, which destroys the climax stage, opens up space and reinitiates succession.

2. Gigartina colonizing the plots where Sousa had removed Ulva and where he had left Ulva in place at the same rates would be consistent with the tolerance model.

3. The facilitation model would have been supported if Gigartina had colonized the plots where Ulva was left in place at a higher rate compared to where Ulva had been removed.

Concept 20.4 Review Answers 1. Succession is the basis for resilience. Remember that part of our definition of succession was a change in plant, animal, and microbial communities in an area following disturbance.

Consequently, it is succession that restores a community disrupted by disturbance.

2. The Park Grass Experiment suggests that the apparent stability that emerges when a coarse level of taxonomy is used— grasses, legumes, and other species (see fig. 20.24)—disappears when all plants are identified to species (see fig. 20.25).

3. Higher nitrate concentrations were associated with higher levels of resilience in Sycamore Creek, Arizona (see figs 20.27 and 20.28).

Chapter 21

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Concept 21.1 Review Answers 1. Because they are less continuous, forested areas make up the patches in these landscapes, while deforested land is the matrix.

2. Forest succession has the potential to increase forest cover in landscapes such as those shown in figure 21.4, joining isolated forest patches to form continuous habitat for forest birds.

Eventually succession could transform patchily distributed forest habitat into the landscape matrix, reducing open grassland habitat to isolated patches surrounded by forest.

Concept 21.2 Review Answers 1. The patterns shown in figure 21.11 suggest that small patches of prairie are unsuitable habitat for Sigmodon, which should be more seriously impacted by fragmentation of prairie habitat than either Microtus or Peromyscus.

2. Increasing the movement of individuals between isolated habitat patches will reduce the probability of extinction of formerly isolated populations.

3. Increasing the movement of individuals between habitat patches by creating habitat corridors can also speed the spread of infectious disease between populations.

Concept 21.3 Review Answers 1. Keystone species and landscape engineers both exert major influences on communities and ecosystems. Though ecosystem engineers may also be keystone species, the concept of ecosystem engineering limits the primary mode of influence by ecosystem engineers to their changing the physical environment. In addition, ecosystem engineers may be abundant, while keystone species are not (see fig. 17.17).

2. A dominant species of tree in a forest or coral on a coral reef create major changes in the physical structure of the communities they occupy and have been referred to as ecosystem engineers (Jones, Lawton, and Shachak 1994). However, they are more often referred to as ―foundation species‖ (see Suggested Readings, Ellison et al. 2005).

3. Analysis of pre- vs. post fire suppression landscapes is necessary to test Minnich’s hypothesis because the specific variable that he was interested in testing was practice of fire suppression. It is important to control for factors other than fire management practices that may contribute to differences in burn area between these two regions, including climatic differences, differences in the age structure of the vegetation, and topographic differences.

Chapter 22 Concept 22.1 Review Answers 1. Fragmentation of habitat not only affects populations but also community properties. The number of species living in habitat fragments is known to decrease with decreased fragment size and increased fragment isolation.

2. One of the main sources of the variation in number of mammal species on isolated mountain ranges at a given distance from large montane areas are differences in the area of montane habitat on the mountain ranges (see fig. 22.3).

Concept 22.2 Review Answers 1. Estimates of immigration and extinction rates on islands underestimate the true rates, since they are based on surveys of species at two points in time and do not include species that immigrated and went extinct between two surveys of species. The only way to obtain an accurate estimate of the true rates would be to monitor the island biota continuously.

2. Diamond would have had a basis for rejecting the equilibrium model of island biogeography if during his studies of the California Channel Islands he had observed no (or very little)

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turnover in bird species. Such a result would have indicated that the island bird communities are static and not the result of a dynamic balance between rates of immigration and extinction.

3. Ethical considerations draw substantial attention in the ecological and behavioral sciences.

Researchers around the world are increasingly asked by funding agencies and professional journals to justify scientific research that involves the killing of animals, including invertebrates, or causes habitat destruction.

Concept 22.3 Review Answers 1. The large number of factors of potential importance, the vast diversity of organisms involved, and the large scale of the phenomenon make it unlikely that a single factor will explain latitudinal gradients in species diversity.

2. Diversity on islands and diversity on continents are positively correlated with area (compare figs. 22.20 and 22.21 with figs. 22.5 and 22.6).

Concept 22.4 Review Answers 1. History should have a major influence on regional diversity patterns, since the diversity within a region is the consequence of a historical process involving relative rates of speciation and extinction within the region and immigration and extinction of species colonizing from other regions. Unless these rates are equal across all regions, regional differences in diversity will arise over time.

2. In the case of Mediterranean floral diversity, the region with the smallest area supports the greatest number of species, while the three temperate forest regions, despite being equal in area, differ several-fold in regard to the number of tree species. The combined weight of these two independent studies, which shows that area is of little importance, lends greater support to the hypothesis that historical effects can have a major influence on diversity patterns than would the results of a single study.

Chapter 23 Concept 23.1 Review Answers 1. Because they are mediated through the effects of a physical factor (precipitation), the influences of El Niño and La Niña on ecosystem structure and processes are generally considered as examples of bottom-up control.

2. El Niño, a source of greater than average precipitation in the Great Salt Lake region, exerts bottom-up control on populations of the predaceous insect, Trichocorixa verticalis, by reducing the salinity of the limnetic zone of the lake. However, once it moves into the limnetic zone, T. verticalis exerts top-down control on grazing zooplankton, creating a trophic cascade.

3. The example of El Niño and the Great Salt Lake suggests that populations, communities, and ecosystems are subject to both top-down and bottom-up controls, that both sources of control are ecologically significant, and that it is not possible in many, perhaps most, cases to disentangle those influences.

Concept 23.2 Review Answers 1. Increasing inputs of nitrogen to aquatic systems can lead to eutrophication, particularly of coastal marine waters.

2. Increasing nitrogen in terrestrial ecosystems can alter the mutualistic relationship between mycorrhizal fungi and plants, and lead to reduced plant and fungal diversity.

Concept 23.3 Review Answers

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1. Reducing forest area threatens biodiversity, since diversity is positively correlated with the area of available habitat at scales ranging from small mangrove islands to entire continents.

Where area of habitat has been reduced, for instance in Simberloff’s experiments (see fig.

22.14), diversity has declined consistently.

2. The threats include converting a formerly continuous population into a metapopulation, reducing gene flow between sub-populations, and increasing the probability of local extinction.

3. The ecological impact of deforestation is always greater than the area of forest removed, since the interior environments of isolated forest fragments are altered for a significant distance from the boundary of the fragment as a result of edge effect.

Concept 23.4 Review Answers 1. The evidence strongly supports the following: (1) atmospheric CO2 has increased substantially in the past two centuries and now exceeds all levels reached during the past 800,000 years; (2) global temperatures correlate positively with atmospheric CO2 levels; and (3) the burning of fossil fuels is making a major contribution to the high levels of CO2 currently in the atmosphere.

2. Earth has warmed by about 0.8°C in the past century. Greenhouse gases trap heat near the surface of the earth and contribute to the current increases in global temperatures. Global warming is responsible for accelerated melting of glaciers, increasing drought in semiarid regions, increasing the incidence of wildfires, and global warming is also implicated in recent and future extinctions of plants and animals.

3. There is still some uncertainty regarding how much global temperatures will increase in response to predicted increases in greenhouse during the 21st century.

4. The history of CFCs in the atmosphere as a consequence of the Montreal Protocol offers encouragement to the potential for reversing the buildup of atmospheric CO2 by demonstrating that concerted global action can reduce our impact on the composition of the atmosphere.

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