Concept
The mesopredator release hypothesis is an ecological theory used to describe the interrelated population dynamics between apex predators and mesopredators within an ecosystem, such that a collapsing population of the former results in dramatically increased populations of the latter. This hypothesis describes the phenomenon of trophic cascade in specific terrestrial communities. A mesopredator is a medium-sized, middle trophic level predator, which both preys and is preyed upon. Examples are raccoons, skunks, snakes, cownose rays, and small sharks. The term "mesopredator release" was first used by Soulé and colleagues in 1988 to describe a process whereby mid-sized carnivorous mammals became far more abundant after being "released" from the control of a larger carnivore. This, in turn, resulted in decreased populations of still smaller prey species, such as birds. This may lead to dramatic prey population decline, or even extinction, especially on islands. This process arises when mammalian top predators are considered to be the most influential factor on trophic structure and biodiversity in terrestrial ecosystems. Top predators may feed on herbivores and kill predators in lower trophic levels as well. Thus, reduction in the abundance of top predators may cause the medium-sized predator population to increase, therefore having a negative effect on the underlying prey community. The mesopredator release hypothesis offers an explanation for the abnormally high numbers of mesopredators and the decline in prey abundance and diversity. The hypothesis supports the argument for conservation of top predators because they protect smaller prey species that are in danger of extinction. This argument has been a subject of interest within conservation biology for years, but few studies have adequately documented the phenomenon. One of the main criticisms of the mesopredator release hypothesis is that it argues in favor of the top-down control concept and excludes the possible impacts that bottom-up control could have on higher trophic levels.
