Equilibrium Essay ⋆ Environment Essay Examples ⋆ EssayEmpire

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Equilibrium is a term from general systems theory that has been a central concept in ecology for several decades. In general systems theory, equilibrium is a steady state (homeostasis) that the system achieves due to negative feedback, causing changes in the system to quickly return to the initial state. In terms of ecology, equilibrium occurs when a biotic community maintains a constant species composition and abiotic nutrients and energy are cycled through food webs such that the amount of energy and nutrients entering the biotic community are balanced by output of these abiotic components. Equilibirium is considered to be reached in late stages of ecosystem development when high biodiversity across all trophic levels and a high degree of niche specialization result in all available environmental resources being cycled through the foodwebs, such that no excess nutrients are available for new species to become established. Equilibrium is closely tied to the hypothesis that high biodiversity conveys ecosystem stability, and has been a fundamental concept behind modern conservation design.

A Function of High Biodiversity

Equilibrium occurs as a function of high biodiversity across all trophic levels due to intertrophic and intratrophic competition. Within a trophic level, interference competition between individuals of different species for the same resources causes these species to sort into specialized niches through competitive exclusion. With high biodiversity within a trophic level, species become competitively specialized into very narrow niches with each species having a higher efficiency in resource utilization within that niche, such that all of the resources in question are consumed at that trophic level. Across trophic levels, greater specialization among predators for their prey assures that predator populations are controlled by the individual numbers of their prey species; the predator population fluctuated with that of its prey, and neither becomes extinct. Populations of species are thus controlled from the lowest trophic levels, and species composition is maintained, as no single species is able to consume another into extinction without becoming extinct itself. This encourages greater specialization, thus ensuring available environmental resources are cycled, and maintaining a constant species composition in the ecosystem, which is in a state of equilibrium. The stability of these ecosystems also require sufficient time to pass for competition to sort species into their various niches, in which disturbances do not occur that upset the balance of species.

The equilibrium theory of island biogeography proposes that ecosystems are maintained in a state of dynamic equilibrium. For a given ecosystem, the overall number of species will remain relatively constant over time, although species turnover (the replacement of locally extinct species with new immigrants) occurs. As a study of island environments, the theory asserts that immigration rates into an island are inversely proportional to distance from the nearest continent, extinction rates are inversely proportional to area of the island, and that the equilibrium number of species occurs at the point the two curves are equal. Although originally formulated for predicting biodiversity on oceanic islands, the theory has been widely applied in conservation ecology, with isolated mountaintops and habitat patches within a heterogeneous landscape viewed as functional islands.

Within conservation ecology, the implications of equilibrium have far reaching implications for human-environment interaction. An equilibrium view of nature is one in which species are free to interact and coevolve into stable assemblages over long periods of time. To do so, these systems must be free of disturbance. With disturbance seen as an aberration to these systems, humanity is viewed as having no place in these environments. This scientific view of the environment is rooted in Western ideals regarding the separateness of humanity and nature. Furthermore, these equilibrium perspectives suggest that reserves must have sufficiently large area to prevent extinctions and maintain viable populations of species.

Ecological equilibrium as a model for ecosystem and biodiversity management has been criticized in recent years. First, disturbance has been observed to be a natural and frequent occurrence in ecosystems, such that several terrestrial ecosystems have been identified as functioning within a particular disturbance regime.

Fire ecology is an example of one of these disturbance regimes, whereby midlatitude grasslands and Mediterranean ecosystems, among others, have been identified as being adapted to relatively frequent burnings, such that periodic burning is necessary for proper ecosystem function. Disturbances are seen to occur frequent enough that ecosystems are now often viewed as being in a constant state of flux in terms of species composition and nutrient cycling. Equilibrium is viewed more as an unstable property that an ecosystem may possess at any given moment, rather than as a teleological endpoint that the system naturally gravitates toward. Ecosystems are more frequently described as being in disequilibrium, or nonequilibrium, within the ecological literature.

Second, equilibrium models have been criticized from within conservation ecology itself on philosophical and political grounds. Although equilibrium models provide a politically defensible approach to conservation (an ecosystem’s integrity can only be maintained by being set aside and left undisturbed by people), and there is a tendency to maintain these equilibrium discourses as a result, conservationists criticize equilibrium approaches for encouraging a natural ontology in which nature will return to its natural balance if left alone, and obscures the need for increased human intervention into ecosystems to preserve biodiversity.

Finally, the equilibrium perspective has been used to justify the removal of people from landscapes targeted for conservation reserves. Social and environmental justice concerns have been raised over ecological equilibrium as a result.

Bibliography:

Daniel Botkin, Discordant Har A New Ecology for the Twenty First Century (Oxford University Press, 1991);
William Cronon, , Uncommon Ground: Toward Reinventing Nature (W. W. Norton and Company, 1995);
Robert H. MacArthur and Edward Wilson, The Theory of Island Biogeography (Princeton University Press, 1967);
Eugene P. Odum, “The Strategy of Ecosystem Development,” Science (v.164, 1969);
Michael Soule and Gary Lease, eds., Reinventing Nature? Responses to Postmodern Deconstruction (Island Press, 1995);
Karl S. Zimmerer, “The Reworking of Conservation Geographies,” Annals of the Association of American Geographers (v. 90, 2000).