A mesopredator is a mid-ranking predator in the middle of a trophic level, which typically preys on smaller animals. Mesopredators often vary in ecosystems depending on the food web. There is no specific size or weight restrictions to qualify as a mesopredator, as it depends on how large the apex predator is, and what the mesopredator's prey is. When new species are introduced into an ecosystem, the role of mesopredator often changes; the same happens if a species is removed.
When populations of apex predators decrease, populations of mesopredators often increase. This is the mesopredator release effect. "Mesopredator outbreaks often lead to declining prey populations, sometimes destabilizing communities and driving local extinctions". When apex predators are removed from the ecosystem, this gives the mesopredators less competition and conflict. They are able to catch more prey and have lower mortality rates. Often, mesopredators can take over the role of apex predators. This happens when new species are introduced into an ecosystem or when species leave or are killed off. When this happens, and the new apex predator or former mesopredator, becomes the new species on top of the food chain, it is important to remember that they are not ecologically identical to the former apex predator, and is likely a smaller species, which will have different effects on the structure and stability of the ecosystem. The mesopredators that become the new apex predators are the species that benefit from this mesopredator release. Apex predators reduce mesopredator populations, and change mesopredator behaviors and habitat choices, by preying on and intimidating mesopredators. This can occur in any ecosystem with any type of relationship between predator and prey. However, in the case of the relationship between apex predator and mesopredator, it could mean that the apex predator causes the mesopredator to leave the ecosystem, again, creating room for a new species to become mesopredator. Mesopredator outbreaks are increasing in fragmented habitats. A main cause is the disappearance of apex species within the habitat. Apex species are usually larger animals who require a bigger area and will often leave if the habitat is lost. When the apex predator leaves the ecosystem, a former mesopredator will become the new apex predator. Likewise, the apex predators, being larger animals, will often have more encounters with humans, leaving them more susceptible to harmful conflicts. These harmful conflicts can either cause the apex predator to leave the ecosystem in fear of danger, or if the situation is extreme enough, the humans will have killed off the apex predator. Another reason why mesopredator outbreaks are becoming more popular is because of certain resources being added in fragmented areas. Resources such as pet food, trash, crop, and crop pests. These resources often appear when development is occurring on land near the ecosystem. This scenario is the most ideal for mesopredator outbreaks to occur.
