Predator/Prey Relations

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.