A keystone species—which can be any organism, from animals and plants to bacteria and fungi—is the glue that holds a habitat together. It may not be the largest or most plentiful species in an ecological community, but if a keystone is removed, it sets off a chain of events that turns the structure and biodiversity of its habitat into something very different. Although all an ecosystem’s many components are intricately linked, these are the living things that play a pivotal role in how their ecosystem functions. Keystone species maintain the local biodiversity of an ecosystem, influencing the abundance and type of other species in a habitat. They are nearly always a critical component of the local food web. One of the defining characteristics of a keystone species is that it fills a critical ecological role that no other species can. Without its keystone species, an entire ecosystem would radically change—or cease to exist altogether. It’s important to note that a species’ role can change from one ecosystem to the next, and a species that is considered a keystone in one environment may not be considered the same in another.

Source: ForumIAS