An ecosystem can be defined as a more or less self-contained function unit in ecology consisting of all abiotic and biotic interactions in a specific area. Flow of energy within an ecosystem is a one-way process; Photosynthesis utilizes light (solar) energy to yield chemical energy that is passed on to organisms at significantly reduced amounts at each level of nutrition. This ‘inefficiency’ in energy transfer is the principal constrain in the food chain length. Food chains can be identified as the sequence of organisms through which energy flows. Moreover, food chains and food webs-of greater complexity-describe the complicated feeding relationships between the members of a community in an ecosystem and a variety of them exists.
Food web research is an area of extensive research and interest and early research started by Ch. Elton that first introduced the pyramid of numbers. Following research by others further contributed scientists understanding of food web complexity via their work. Most recent research into food webs and food chains, discussed in this essay, deals with the effect of climate change and pollution in aquatic ecosystems.
History of research into food webs
Charles Elton was a pioneer in the concept of food webs, chains and sizes. His organization of species into functional groups; producers, consumers, decomposers described the characteristic pyramidal shape of food webs, with a larger amount of producers (autotrophs) at the bottom and successively smaller amounts of heterotrophs on the following, higher levels (Elton C.S., 1926). The Eltonian pyramid of numbers is the basis in describing all food webs. It is based on this pyramid that Raymond L.Linderman published his work upon examining it in terms of trophic dynamics. Linderman (1942) suggested that the Eltonian pyramid resulted from a successive loss of energy going up trophic levels, which was attributed to the thermodynamic inefficiency of energy transformation (ecological efficiency).
Robert Paine’s work on intertidal shores, which suggested that maintenance of species diversity and ecological stability were a key result of food web complexity, was the one that raised awareness and interest of numerous theoretical ecologists. One such example is, Stuart Pimm, whose book discusses amongst other, hypotheses of the food chain length (science.jrank.org, 2012).
Food chains and food webs
A food chain is a feeding hierarchy in which organisms in an ecosystem are grouped into nutritional levels. Successive trophic levels represent the flow of food energy and the feeding relationships between them. Food chains usually start with photosynthetic producers because, uniquely, producers have the ability of extracting both energy and matter from the abiotic environment (Communities and ecosystems-KCTS Home). All other living organisms acquire their energy and matter by feeding on other organisms, or breaking them down, recycling their minerals and elements in the process. In nature, three main types of food chains have been observed; the grazing food chain (Fig.1), the parasitic food chain and the detritus food chain (Fig.2).
Figure [ 1 ]: Primary producer consumed by herbivore which in turn is consumed by carnivore
Figure [ 2 ]: The primary consumer (woodlouse) now feeds on detritus (dead leaves)
(Images taken from http://fany.savina.net/2010/02/ecology/, 8 February 2012) Figure [ 3 ]: Representation of a food web in a forest with various interconnecting food chains Image taken fron http://www.tutorvista.com/content/biology/biology-iv/ecosystem/food-web.php , 10 February 2012
In reality, in one habitat, most animals have various food sources, and food chains can be interlinked at different trophic levels to form a complex interaction between different species (PRINCIPLES OF ENVIRONMENTAL SCIENCE AND ENGINEERING- CE O71.) at a food point of view; a food web...