A Mesopredator is a predator that occupies a mid-ranking trophic level in a food web.[1] There is no standard definition of a mesopredator, but mesopredators are usually medium-sized carnivorous or omnivorous animals, such as raccoons, foxes, or coyotes.[2] They are often defined by contrast from apex predators or prey in a particular food web.[3] [4] Mesopredators typically prey on smaller animals.
Mesopredators vary across different ecosystems. Sometimes, the same species is a mesopredator in one ecosystem and an apex predator in another ecosystem, depending on the composition of that ecosystem. When new species are introduced into an ecosystem, the role of the mesopredator often changes; this can also happen if species are removed.
See main article: Mesopredator release hypothesis. When populations of an apex predator decrease, populations of mesopredators in the area often increase due to decreased competition and conflict with the apex predator. This is known as the mesopredator release effect, which refers to the release of mesopredators from the trophic cascade.[5] These mesopredator outbreaks can lead to declining prey populations, destabilize ecological communities, reduce biodiversity, and can even drive local extinctions.[4]
Typically, mesopredators are in competition with apex predators for food and other resources. Apex predators reduce mesopredator populations and change mesopredator behaviors and habitat choices by preying on and intimidating mesopredators.[6] When apex predator populations decline, mesopredators can access hunting and den areas once controlled by the apex predators, essentially assuming the role of an apex predator. However, mesopredators often occupy different ecological niches than the former apex predator and will have different effects on the structure and stability of the ecosystem.
Mesopredator outbreaks are becoming more common in fragmented habitats, which are areas where a species' preferred environment is broken up by obstacles. Fragmented habitats can be caused by geological or human activity, and particularly affect larger animals that roam and hunt across large territories, such as apex predators.[7] Fragmented habitats can drive these species to leave and find more suitable habitats.
Additionally, in many fragmented habitats, apex predators have more encounters with humans, leaving them susceptible to harmful or deadly conflicts, sometimes resulting in eradication of the apex predator population entirely. Human development also promotes mesopredator outbreaks through increasing access to resources such as pet food, trash, and crops.
The mesopredator release effect is not entirely understood. Most research has been conducted on mammal species, with limited studies on non-mammal animal species. Additionally, it is not well understood how these dynamics may play out in ecosystems with many mesopredator and apex predator species.