Behavioural Ecology 2: Family, Society, and Evolution
Biology 208 Dr. Andrew Derocher Text material: Ricklefs Chapter 12
Home range – area within which an animal normally lives. The boundaries of the home range may be marked -usually shared use or, “that area traversed by the individual in its normal activities of food gathering, mating and caring for young” (Burt 1943) -polar bears, white-tailed deer, elk
Home ranges of 3 female polar bears
Territoriality or Space use • Mobile animals • Use of space is not random and only a subset of area is used • Typically working in 2 dimensions (m2 or km2) • Very often temporal dynamic in space use – varies with season, sex, age, reproductive status
• Territorial behaviour evolves to ensure access to crucial resources – food, shelter, access to mates, nest sites, spawning sites, sexual display sites, hibernation sites, resting areas etc.
• Type of territoriality for a species is an interaction of evolution of behaviour and ecology
Home range estimators 2 dimensional area Many different methods used to estimate area
Minimum convex polygon Kernel analysis
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Minimum convex polygon
Eastern Diamondback Rattlesnake (Crotalus admanteus) home range
• Older method used to estimate home range • Basic and easy to calculate but can include a lot of area not actually used • Sensitive to excursions from “normal” area
Kernel home range Display probability areas -blue 50% -green 95%
Territory – area occupied by an animal, pairs, or a group of animals that is defended against intruders -exclusive use by animal or group - e.g., wolves, badgers, breeding song birds, squirrels Maritory – a marine “territory” -bearded seals, Weddell seals, killer whales Home range
Territory
♀ 22-705 m2 ♂ 48-1059 m2 (50% kernel area) From http://www.bio.davidson.edu/Biology/midorcas/GISclass/GISprojects/grayson/grayson.htm
Economic defensibility • territorial behaviour is advantageous if the costs of defence are outweighed by the benefits (here we are talking evolutionary benefits - fitness) • energy used to maintain a territory cannot be used for other activities (e.g., reproduction) • risks involved are increased risk of predation (territorial displays), risk of injury in defence, increased energy costs
European badger territories
Distribution
New Holland Honeyeater Phylidonyris novaehollandiae
Banksia spp.
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New Holland honeyeater territory size increases as the abundance of the nectar-producing Banksia flowers decreases
Territory and body size • Additional support for economic defensibility hypothesis
• territory size increases with body size – increase is faster for carnivores than herbivores due to carnivores being higher in food web – prey are at lower density than vegetation
Fig. 12.4
Social systems Social system – the characteristic size and composition of a group and the nature of the behavioural interactions among its members Sociobiology – study of the biological basis of social behaviour
Social system described via 3 features 1. Group size and structure -# of individuals, age structure, and sex composition
2. Mating system -duration of association, relative # of each sex
3. Cooperation and helping -level of cooperation in hunting and raising young, genetic relationships
Group size • Temporal component (even solitary species must come in contact to mate) – different forms of communication can alter the perception of a group (temporal and spatial)
• Habitat structure relevant (are the individuals together because of interactions or forced by habitat)
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• Solitary species – bears, cougar, lynx, raccoon, most mustelids (weasel family) – Common in top predators
Aggregation – groups of animals that occurs when individuals are attracted to an environmental resource. Does not imply any social organization. Grizzly bears at McNeil Falls, Alaska
• Group species – wolves, hyenas, African lion
© B. Davidson
Colony – any group of organism living together or in close proximity to each other; refers to an integrated society in which member may specialized subunits (division of labour)
Group – a band, party or assemblage of individuals without regard to degree of social organization (intermediate between an aggregation and a colony) - can have large temporal variation
Termite hill, Kenya
Bighorn sheep herd G and B Corsi © California Academy of Sciences
Advantages and disadvantages of living in groups Evolutionary “decision” to join a group is based on the relative advantage of solitary vs group life benefits: shared prey, ability to kill larger prey, group defence, warning of predators, group rearing of young
detriments: intraspecific competition, reduced access to breeding opportunities, sharing of resources European goldfinch
Vigilance – time spent looking for predators
Fig 12.5
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Kin selection Selection acting on one or more individuals and favouring (or disfavouring) the survival and reproduction of relatives (other than offspring) that possess the same genes by common descent – e.g. altruistic behaviour between related individuals – Alarm calls of ground squirrels when predators approach
Cooperation and helping
African hunting dogs
Increase (+) or loss (-) in inclusive fitness
Fig 12.5
Group hunting energy return
+
e rem Inc
nt A
T ot Benefit of group al i nc defense (A+ remen B) t Increment B
0
Optimal group size Number of members in group, N
Acorn woodpecker • Social unit is up to 12 (both ♀ and ♂) • Gather and store acorn in trees
Honey bees -females are diploid (2N) -males are haploid (1N) called haplodiploid Due to the genetic structure, a sibling is more related to its siblings than to a parent
– Division of labour – Mate sharing – Infanticide
G. W. Robinson © California Academy of Sciences
• System likely occurs because of food supply and habitat saturation
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Naked mole rats Eusocial – truly social Extensive cooperation – group tunnelling Division of labour – breeders produce young non-breeders defend tunnels, clean Queen – largest individual is the only female to breed Up to 28 pups/litter! Live in east Africa
Evolutionary Stable Strategies (ESS) • Assemblage of behavioural or physical characters (a ‘strategy’) of a population such that, if all members of a population adopt it, no alternative strategy can invade. • Can be applied both to genetically determined physical characters (such as horn length) and learned behaviour (e.g., whether to fight or retreat from an opponent). Better explained by an example…..
• Self-interest rules behaviour among non-related individuals • Natural selection favours fitness so cooperation could evolve within societies –BUT a single selfish individual can greatly increase their fitness by cheating
Hawks and Doves
Hawks and Doves • Consider 2 behaviour patterns in a population – Hawks are aggressive and will always battle for resources – Doves are passive will never fight • A population of 100% doves is unstable; if a mutation caused the introduction of a single hawk, it would have an immediate advantage, and the hawkish behavior would bully the doves out of existence. • But a population of 100% hawks is also unstable. A single dove introduced by mutation would have a long-term advantage because the hawks' constant fighting leads to frequent injury, while the dove, refusing to fight, escapes that risk.
B = benefits C = costs • 2 hawks fight for a resource get ½ the BENEFIT but incur the COST so ½B – C • 2 doves come to a resource and each get ½B but no COST • Things get more complex when we consider that the average “payoff” (fitness) to hawks and doves depends on the relative proportion
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ESS • Using game theory, John Maynard Smith showed that there is a particular ratio of hawks to doves that forms what he called an "evolutionary stable strategy" for the two species – pure hawk or pure dove populations are not stable
Fig. 12.14
John Maynard Smith 1920-2004
Selection can work to maintain a balance of different characteristics in the population –doves can survive in a hawk population when the cost of the hawk strategy is very high –this results in both hawks and doves in the population and an evolutionarily stable mixed strategy Fig. 12.15
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