In the field of ecology, classifying a species as a generalist or a specialist is a way to identify what kinds of food and habitat resources it relies on to survive. Generalists can eat a variety of foods and thrive in a range of habitats. Specialists, on the other hand, have a limited diet and stricter habitat requirements.

Raccoons (Procyon lotor) are an example of a generalist species. They can live in a wide variety of environments, including forests, mountains, and large cities, which they do throughout North America. Raccoons are omnivores and can feast on everything from fruit and nuts to insects, frogs, eggs, and human trash. Other examples of generalist species include bobcats and coyotes.

An example of a specialist species is the koala (Phascolarctos cinereus). Native to Australia, koalas are herbivorous marsupials that feed only on the leaves of the eucalyptus tree. Therefore, their range is restricted to habitats that support eucalyptus trees. Within this diet, some koalas specialize even further and eat leaves from only one or two specific trees.

An example of a carnivorous specialist is the Canada lynx (Lynx canadensis), which preys upon snowshoe hare. Canada lynx (Lepus americanus) inhabit the forested, mountainous areas favored by their prey, and are well-adapted to hunting in deep, soft snow.

Like the koala and the Canada lynx, specialist species evolved to fit a very specific niche. This can pose a problem when environmental disruptions, like effects from climate change or habitat loss, occur. Such disturbances have a strong effect on specialists because they cannot adapt to use other food sources or habitats as quickly as generalist species. In fact, some scientists have found that the number of specialist species is declining due to human activity, and the number of generalist species is on the rise.