mesopredator release, in ecology, a phenomenon in which populations of medium-sized predators rapidly increase in ecosystems after the removal of larger, top carnivores. Such rapid increases in mesopredator populations can force sudden changes in the structure of ecosystems as these animals assume new roles and greater influence.

Mesopredators, such as coyotes (Canis latrans), red foxes (Vulpes vulpes), and raccoons (Procyon lotor), are typically outcompeted by top carnivores, such as wolves (Canis lupus) and cougars (Puma concolor). for food and other resources. Because top carnivores are also capable of killing and eating them, mesopredators often avoid areas claimed by top carnivores or alter their hunting and foraging patterns to reduce the chances of an encounter. In the absence of larger predators, mesopredators can claim the hunting grounds, den sites, and food resources once controlled by top carnivores. Rising populations of mesopredators place substantial pressure on their prey, such as songbirds and small mammals, causing many such species to suffer dramatic declines. Compared with ecosystems having top carnivore populations intact, ecosystems experiencing mesopredator release have lower levels of biodiversity.

One notable example of mesopredator release occurred in North America during the 20th century, when cougar and wolf populations declined dramatically in the conterminous United States as a result of overharvesting by hunters and collectors and poisoning by ranchers. With these top carnivores effectively eliminated from most ecosystems, a major source of mesopredator mortality was removed, and populations of coyotes, foxes, raccoons, and other mesopredators increased.

Mesopredator release is not restricted to North America. The decline of leopards (Panthera pardus) in some parts of Africa during the late 20th century allowed baboon (Papio) populations to rise, increasing the conflicts with humans. In addition, the loss of large sharks in the oceans allowed smaller-bodied sharks and rays to increase. In one case, the cownose ray (Rhinoptera bonasus), freed from persecution by large sharks, decimated the North Carolina scallop fishery between the late 1980s and early 2000s.