TREK Program
Social Studies
Field Studies – Background Information Introduction Education about the natural environment and sustainability are fundamental components of the TREK Program. Understanding and connecting with the natural world means building and nurturing sustainable communities in which we can satisfy our needs and aspirations without diminishing the chances of future generations. For this task we can learn valuable lessons from the study of ecosystems, which are sustainable communities of plants, animals, and micro-organisms. To understand these lessons, we need to learn the basic principles of ecology: energy flow; cycling; interrelationships; and change.
Energy Flow Sunlight streams through space to bathe the surface of this planet each day. Green plants are the only living things which can directly capture this energy from our parent star. Through the process of photosynthesis they package the sun’s energy into molecules of sugar which build leaves, roots, seeds, and other plant tissues. As animals eat and digest the plants, they open these packages of sunlight energy and use that energy to build their own tissues. And the energy travels even farther when another animal (such as a hawk) eats the plant-eater (such as a rabbit). We call this pathway along which energy flows from the sun to plants to plant-eaters to animal-eaters, a food chain. As energy flows along a food chain, much of it is used up and lost. Before they are eaten, plants use up much of their energy to grow, and animals use up a great deal of the sunlight energy from their food as they move around. Because of this energy loss, there is less energy available farther up the food chain, so in most food chains there are many plants, fewer plant-eaters, and even fewer animaleaters. Those animals with positions at the ends of such food chains are called top predators. Humans are one of these. However, most humans on the earth today are vegetarians because they cannot squander the captured sunlight energy available to them in the plants by passing it first through an animal. When someone says it is better for you to eat lower on the food chain, he or she is referring to this loss of available sunlight energy. In terms of overall flow of sunlight energy on the earth, life is arranged in pyramids – a broad base of plants supports fewer and fewer animals as the pyramid of captured sunlight energy flows upwards through the plant and animal life in the area. It takes about ten times more plants at the base of a pyramid to support those animals at the next level. And those animals will only be able to support 1/10th of their number in the level above them, and so on. This means that in our energyintense societies it takes about 100 pounds of grain to produce 10 pounds of beef to produce a 1 pound gain in your weight.
Pyramid of Life Energy Plant and Animal-eaters
(omnivores) e.g. humans, crabs, opossums
Eaters of Animal-eaters
(secondary carnivores) e.g. tuna, falcons, killer whales
Animal-eaters
Decomposers
(detritivores) eat dead tissues and waste products of other organisms e.g. fungi, bacteria, worms
(primary carnivores) e.g. spiders, warblers, wolves
Energy Plant-eaters
(herbivores) e.g. termites, grasshoppers, water fleas, deer, geese
Plants
(photosynthesizers) food creators e.g. aquatic (water) and terrestrial (land) plants
Nutrients from the Soil
Water
Nutrients from the Air
Energy Flow - continued In the beginning, humans, like all other animals, obtained all of their sunlight energy by eating the plants, or eating other animals that had eaten the plants. Later in learning to use fire, and to harness other animals, they discovered indirect ways of tapping into sunlight energy. A major development in the human manipulation of sunlight energy came in the form of cultivating hard-encased seeds. In these small, durable packages of sunlight they found a marvellous device. Now, they could easily store sunlight energy for the future or grind it up and carry it along with them as they spread out over the earth. It would be hard to underestimate the importance of this development in terms of the success of the human form of life. Since the movement of both air and water on the earth is governed by the energy of the sun, they, too, represent indirect sources of sunlight energy that the human species draws upon. Wind and water power would contribute greatly to the human impact upon the other life here, but it wasn’t until they tapped into the fossil fuels buried beneath the surface that the impact and the pace of human activities began to threaten much of the other life on the earth.
Cycling The basic building materials of life are hydrogen, carbon, oxygen, nitrogen, phosphorus, and sulphur. There is a limited amount of these materials on the earth, so they must be reused over and over again. For millions of years they have been taken from and returned to the air, soil and waters of the earth by all living things. The soil is the great nourisher of plants, providing the nutrients which they need to grow. The soil would be useless if there was no way of getting these nutrients back after they had been taken up by the plants. But soil is constantly being replenished, for there are millions of bacteria in each handful of soil that break down waste matter and dead animals and plants, and thus return to it the nutrients which those things contain. Imagine for a moment that you are holding a big handful of rich soil. Do you know what you would be holding in that single handful? About 5,000,000,000 living plants. That’s right, there are about five billion micro-organisms in a single handful of rich soil. Not only that, there are about a million animals in that same handful – eating the plants right in your hand. The point is, that it isn’t dirt. All living things on the surface of the earth go from soil to soil. And so the soil cycle continually recirculates the building materials of life. Water is the liquid of life on earth, and it is moved by the heat of the sun through an enormous cycle of its own. Water evaporates from the rivers, lakes and oceans of the world and rises into the sky where it condenses into clouds. From there the water falls back to the earth in the form of rain, snow, sleet or hail, only to flow once again into the rivers, lakes and oceans of the world. Occasionally, the water takes a detour through a living thing. Evaporation and the filtering action of the soil are important purifiers in this water cycle, the largest physical process on earth. Parts of the air surrounding the earth are also used over and over again as well. With every breath, animals of the earth exhale carbon dioxide. Plants use this carbon dioxide from the air when they make sugar in their leaves, and a by-product of the sugar-making process is oxygen, which the plants release into the air. Thus the air cycle provides for the exchange of essential needs of life for both plants and animals. Stop right now and focus on your breathing for a moment. Go ahead, take a deep breath and just hold it while you read these words… how far down the page do you think you will get? You can go for some time without food or water, but only a few moments without air. However, our air-breathing habit is so much a part of us that we don’t even think about it – taking about 17,000 breaths a day, every day of our lives. Together, these three great cycles of the building materials of life explain how the matter of the earth is reused – recycled if you will – by all living things through eons of time. It also suggests the potential long-term effects of synthetic, human-made substances that have been indiscriminately introduced into these cycles without adequate knowledge of their impact. Stop right now while you are reading this page and pinch yourself. Go ahead, really do it … no one’s watching. Now, just hold on to that fold of flesh for a moment. Do you know that chances are good that between your fingers right now there’s a speck of a … dinosaur? That’s true! You see, whether it is flower or fly or flesh doesn’t make any difference. It is all the same building material, and those materials have been used over and over again for a very long time in the systems of life on the earth.
Interrelationships Picture the earth as a ball travelling through space, covered with a thin layer of air, water and soil, warmed and energized by the sun. The quantity and quality of air, water, soil, and sunlight in this layer varies greatly over the surface of the planet. And this intermixing of energy and materials has produced a great variety of conditions for life on the earth. From the deserts to oceans, from the arctic to the tropics, from the mountains to the plains, the available energy and building material varies greatly. In turn, this tremendous variety of conditions is the reason for the dazzling diversity of living things on the earth. Each living thing is the result of a unique combination of sunlight, air, water and soil, and so is different from every other living thing. A community is a mixed group of plants and animals occupying a specific area of the surface of the earth. Living things are grouped together in these specific areas because it is in such places that they can best meet their energy and material needs. The actual place where something lives in a community, the place where it meets its needs of life, is called its home or habitat. A habitat may be as small as a beetle’s tiny crevice in the bark of a tree, or as large as an eagle’s vast hunting ground; a good habitat takes up as much space as the plant or animal needs to find its water, food and shelter. The role or job in the community performed by a plant or animal is called its niche. For example, most squirrels occupy the niche of a tree-climbing seed-eater, while a common bat’s niche could be described as that of a night-flying insect –eater. Together, the habitat and niche of an individual plant or animal spells out its “address” and “profession” within its community. Over time living things tend to fill all available habitats and niches in a community, and communities appear to function more smoothly when a variety of living things are all doing their “jobs” within them. Living things interact within their communities in a variety of ways. Although many things we see may be in competition with one another for their energy and material needs, under the surface there is also an amazing amount of cooperation. Everything on the earth is somehow connected to everything else. It would be impossible for any form of life to exist by itself.
Change Each living thing has a unique combination of features and behaviour patterns to solve its problems in gathering and using matter and energy. Each has a built-in strategy which provides it with the means to survive – a strategy which enables it to protect itself, get food and water, and reproduce. These adaptations may take the form of special features, such as the webbed feet of an otter, the pincers of a crab, or the thorns of a shrub. In addition, the behaviour of an individual may also be part of this strategy. Some trees lose their leaves in the winter, birds often fly seasonally to warmer climates, and many creatures are active at night when they can be protected by darkness. However, life is not static. Over time, forms of life appear with better fitting features and behaviour patterns and replace those which are less prepared. This process is the cutting edge of the success of life on earth: the best fit forms survive over time because those individuals live to reproduce and pass along their improved strategies. This variety also produces an overall endurance and stability. It assures that something can always take advantage of changes in the surrounding conditions. It seems to guarantee that life will succeed in filling nearly every condition on earth, and out of the earth’s tremendous pool of living things, something will always be able to survive and life will continue. Everything on the earth is in the process of changing. In the lives and deaths of plants and animals, in the tides and winds, in the movement and flow of rock within the earth itself, we witness a dynamic, constantly changing planet in action. Many changes on the earth occur so slowly that we cannot see them happening. The growth and movement of continents, glaciers, mountains and valleys takes thousands upon thousands of years. These and many other major earth changes require enormous amounts of geologic time as their most important ingredient. Certain changes in natural communities happen in a series of distinct stages. One such change is the succession of a new kind of plant which is able to live in the shade or soil built up by another kind of plant. A series of such stages can, over a long period of time, cover bare rock with a forest, and even though we could not witness the whole process in one lifetime, we can often see one or two of the stages of such a change taking place. Change. It is our measure of the ebb and flow of energy. Sunlight energy bathes the surface of our planet each day. It is captured by the plants and taken from them, in turn, by an amazing array of animal life – from a tiny sponge to a gigantic whale. It is the upward push of captured sunlight energy that overcomes the downward pull of gravity, and produces the earth’s colourful kaleidoscope of living things.
Developing Our Understanding of the Natural World The basic principles of ecology are: energy flow, cycling of matter, relationships, change – and, as a consequence of all those, sustainability. The survival of humanity will depend on our ability to understand these principles of ecology and live accordingly. During your on-TREK term you will examine five different ecosystems in order to develop a firsthand understanding of the principles of ecology. The ecosystems we will explore are: • alpine (mountain tops) • intertidal (ocean) • freshwater (lakes, ponds, rivers) • bog • temperate rain forest The information contained in this background information was adapted from The Web of Life by Fritjof Capra and Earth Education by Steve Van Matre.