Predator/Prey Relations Essay ⋆ Environment Essay Examples ⋆ EssayEmpire

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Predator/prey relations refer to the population dynamics between any heterotrophic species (consumers) and the species that it feeds on. The term “predator” in this usage refers to primary consumers (herbivores) as well as secondary and tertiary consumers (carnivores, top carnivores, and omnivores). The concept is crucial to understanding species demography, trophic hierarchies, ecosystem stability, and biodiversity conservation.

The works of Lotka and Volterra during the 1920s form the basis of much subsequent work. Lotka examined the competitive interactions between species, both in terms of intertrophic competition but also with competition between species for similar resources (interference), in terms of the laws of thermodynamics, bringing the concept of energy flow and efficiency into synthesis with Darwninian competition. This was further elaborated upon by Lindemann, Elton, and MacArthur and ultimately culminated in Odum’s concept of the ecosystem. The Lotka-Volterra model of predator/prey relations describes the populations of both predator and prey species as fluctuating together, with the changes to the predator population lagging behind that of its prey in time. In such a model, neither the predator nor the prey become extinct, as predator populations will decline as prey populations decline, and the resultant decline in predators allow the prey population to recover.

The actual variance in abundance of predator and prey populations is affected by specific characteristics of the predator. A predator that has a narrow range of prey species (a stenophagous predator) will have its populations fluctuate in accord with the predictions of the Lotka-Volterra model. The abundance of the prey species in such a situation exerts a greater control on the populations of the predator, and extinction of either predator or prey species is not likely.

Alternatively, a predator that consumes a wide range of prey species (a euryphagous predator), exerts greater control on the overall abundance of each species, with variable effects on biodiversity. A euryphagous predator can reduce the biodiversity of an area by eating one or more of its prey species to extinction because of its wide dietary range and the presence of other species to feed upon. A euryphagous predator can also increase the biodiversity of an area by limiting the overall abundance of each of its prey species and preventing any one of them from becoming dominant. That is, were the predator to be removed from the environment, the abundance of each prey species would be regulated by interference competition, with a greater likelihood that one or more of these species would be driven to extinction by competitive exclusion.

Ecosystem Stability

These concepts of predator/prey relations are crucial to understanding dominant ideas of ecosystem stability. The general premise of ecosystem stability states that greater native biodiversity within an ecosystem provides stability, where stability is defined as the maintenance of a constant community structure (that is, an ecosystem is considered stable when the species composition does not change). This statement is further elaborated upon to specify that a high level of biodiversity across all trophic levels provides stability. As the number of predator and prey species increases, according to this argument, intratrophic competition increases. Predators become more efficient in and specialized to a narrower niche and hence are more likely to be stenophagous. With a greater incidence of stenophagous predators, control of overall population numbers shifts to the bottom of the trophic levels (producers), extinctions are less likely to occur, and the higher levels of efficiency mean that all environmental resources are consumed and cycled, making it more difficult for a species from outside the ecosystem to become established within it. Hence, species composition remains stable and the ecosystem is considered stable. This line of reasoning has guided conservation practice throughout the latter half of the 20th century and into the 21st.

Species Invasions

In terms of human-environment interaction, predator/prey relations have informed knowledge of the process and management of species invasions. Some factors commonly cited as allowing for the success of an invader in a new environment relate to it often being a generalist predator, and having escaped its natural predators. Hence, some invasive species are seen to drive the extinctions of several prey species that are not adapted to predation by the predator, while the new predator has nothing to keep its own population in check and vastly expands its own numbers at the expense of the native biodiversity.

Managers have used predator/prey models in controlling invasive species, often through biotic control. Biotic control involves introducing a predator species that is stenophagous toward the targeted invasive species, with the reasoning being that this new specialized predator will keep the number of the invasive species down while not preying on the native species in the ecosystem. Nevertheless, examples exist where the biotic control species expanded its dietary range upon being introduced to a new environment, and became a pest as well.

Questions of predator/prey relations also surface in conflicts over conservation efforts, especially in relation to the reintroduction of predators into an environment. For example, during the 1930s wolves were systematically eradicated from the American West because they were seen as livestock pests; this resulted in explosions of populations of primary consumer species such as mule deer and elk. These consumers then were seen to further reduce the biodiversity of the vegetation due to over-browsing.

Conservationists have encouraged the reintroduction of predators such as wolves, bears, and cougars, but these measures are often met by resistance over economic and safety concerns.

Bibliography:

Daniel Botkin, Discordant Harmo A New Ecology for the Twenty First Century (Oxford University Press, 1991);
Charles Elton, The Ecology of Invasions by Animals and Plants (University of Chicago Press, 1958);
Mark V. Lomolino, Dov F. Sax, and James Brown, Foundations of Biogeography: Classic Papers with Commentary (University of Chicago Press, 2004);
Glen MacDonald, Biogeography: Space, Time and Life (John Wiley & Sons, 2003);
Leslie H. Real and James Brown, Foundations of Ecology: Classic Papers with Commentary (The University of Chicago Press, 1991).