Because of their wide-ranging nature, long-term conservation strategies aimed at restoring carnivore populations must target large, diverse, and often ecologically important areas, all of which include many other species. Carnivores are effective surrogates for broader biodiversity conservation planning. Some species; such as wolves, lions, and sea otters; are keystone species, meaning their presence is a critical element to the function of their ecosystems. Through direct predation, carnivores directly impact the diversity and composition of animal and plant communities, a process known as a trophic cascade. Other species, particularly mesocarnivores (an omnivore whose diet consists mostly of meat) like river otters, serve as effective indicator or sentinel species, meaning they are indicative of an ecosystem’s relative health.