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GLACIER National Park |
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 Sun, Green Plants, and Animals The sun is the source of energy for any plant-and-animal community. Green plants draw nitrogen and minerals from the soil, and in a process called photosynthesis use sunlight to convert raw materials (carbon dioxide and water) into carbohydrates (sugar, starch, cellulose), giving off oxygen as a by-product. Besides burning oxygen, animals depend on plants for food. Green Plants, trees and shrubs, grasses and sedges, wildflowers, ferns, mosses, algae and lichens—are fed upon by animals, which are unable to manufacture their own food. The Redback Vole, like other rodents, pikas and hares, seed-eating birds, grazing and browsing hoofed animals, and herbivorous insects, derives its energy from the seeds and other parts of green plants that it eats. The Garter Snake, feeding upon the vole, is dependent upon plants even though it does not eat them. The Great Horned Owl, preying upon the garter snake, is one more step removed from the green plants—but still dependent on them. Scavengers such as carrion beetles feed upon the carcass of the owl; the remains are then attacked by Decomposers, primarily bacteria, that break down the animal tissues into basic organic compounds. The Soil, enriched by the minerals and carbon and nitrogen compounds added to it by the decomposers (and by other processes such as fire) supports new green plant growth. Thus energy derived from the sun flows through the ecosystem in a food chain. A plant-and-animal community is a complex, interlocking web of such food chains. (click on above image for an enlargement in a new window) |
 A Pyramid of Numbers Necessarily, the number of plants in an ecosystem far exceeds the number of plant eaters, and the number of prey species must exceed the number of predators. During its lifetime, a golden eagle will consume a vast number of lesser animals. The combined mass of prey animals necessary to sustain an eagle greatly outweighs the eagle itself. Ecologists refer to this proportional relationship of mass between each link in the food chain as the pyramid of numbers. The diagram represents a numbers pyramid for the alpine zone. Because of its limiting environment, the alpine zone supports a lesser plant mass than the forest zone. As a result, the carrying capacity of the alpine is less than that of the forest. Tertiary (third-order) consumers are the predators (Golden Eagle, Swainson's Hawk, etc.) that feed upon other predators. Because of the 90% loss of energy at each level of the food chain, there will be very few hawks and eagles in comparison to the numbers of marmots. 1 Kilo Secondary consumers are the predators (weasels, shrews, carnivorous insects and birds, etc.) that eat herbivores. The animals at this level of the pyramid are often—though not always—larger than the animals they feed upon. But they are much less numerous, because it takes many prey animals to sustain one predator. 10 Kilos Primary consumers (plant eaters, or herbivores) convert plant tissue into animal flesh. In the process about 90% of the energy stored as plant food is lost, mostly as heat energy. In the alpine community the herbivores include pikas, marmots, ground squirrels, and ptarmigan, as well as herbivorous insects. 100 Kilos Producers are the green plants at the base of the food pyramid, manufacturing food for the animals of the alpine community. The biomass (total weight) of each level of the food chain is ten times (more or less) the weight of the stage above it: 1,000 kilos of green plants will produce only 100 kilos of primary consumers. 1,000 Kilos (click on above image for an enlargement in a new window) |
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Last Modified: Sat, Nov 4 2006 10:00:00 pm PST |