Food Chain. Definition

A food chain is an arrangement of the organisms of an ecological community according to the order of predation in which each member uses the next member as a food source. Although the term was not used until 1913 by the American ecologist Victor Shelford, the concept had already been anticipated by Charles Darwin in 1859 as "the tangled bank" metaphor and developed by the zoologist Karl Semper in 1881. Charles Elton (1927) further developed the concept and promoted food chains as one of the basic principles forming the basis of community ecology.

Since the 1950smuch research has been conducted on food webs (the totality of interacting food chains in an ecological community). Some ecologists—for example, G. E. Hutchinson, R. Paine, B. Menge, P. Sutherland, and G. Polis — studied the complexity of food webs and their importance to community ecology. Others, including R. Lindeman, J. Teal, and H. T. Odum, studied energy transfer through food webs and ecosystems. A detailed mathematical theory describing food-web dynamics has been developed by S. Pimm, R. May, J. Cohen, L. Oskonan, N. Martinez, and others.

Food chain diagrams demonstrate the pathway of food through the ecosystem. Some paths are simple chains, but in most cases paths are more complex and form webs. Illustration layout by V. Medland, some images

Definition. Food webs describe who eats whom in a particular ecological community. In some instances, food webs are simple chains: Species A is eaten by species B, which is eaten by species C, In most cases, species relationships are far more complex: Species A is eaten by species B and species C, which also feeds on species B, The food web of even a relatively simple community would be extremely large and complex. In order to simplify large webs, individual species are commonly placed into groups that have the same predators and prey in the food web.

The trophic level of a species indicates how many links separate its prey from the original energy source, usually the sun. Primary producers or autotrophs are organisms that produce their own food (plants and in some cases autotrophic bacteria). Consumers such as herbivores, omnivores, and carnivores make up the ascending levels.

Decomposers feed on a pool of decomposing organic matter that can come from many trophic levels. Because of this they are often separated into a separate food chain where detritus (loose material resulting from disintegration) makes up the primary food source of the decomposers, which are in turn eaten by carnivores.

It is important to remember that a food web represents only presence or absence of predation between species. In the real world, these interactions are highly dynamic and may vary in presence or importance depending on environmental factors such as season or on biotic (relating to life) or demographic factors such as sex or developmental stage.

Complexity. Few food webs are simple chains. Most involve consumers as omnivores that feed on more than one trophic level, such as coyotes, which are predators that sometimes feed on herbivores such as rabbits or on other predators such as lizards. Consumers can be herbivores (feeding on grasses or fruits) and are often detritivores (scavenging on dead animals). Some species feed at different trophic levels at different life stages.

For example, mosquitoes are detritivores as larvae, whereas females are blood-feeding predators, and males are nectivores (feeding on nectar) or may not feed at all. A measure of complexity called "connectance" has been developed to better understand food-web dynamics. Connectance is the ratio of the number of actual feeding interactions between the members of the food web to the total possible number of interactions. A higher ratio indicates greater complexity. A second critical factor is interaction strength, which is the actual amount of influence one species has on another.

By measuring connectance and interaction strength scientists are able to evaluate the stability of a food web or its ability to remain unchanged following different types of disturbance. It was originally believed that more complex food webs are less stable, but recent studies of food webs with high connectance but weak interaction strengths refute this belief.