What is a keystone species?

A keystone species is one that plays a critical role in maintaining the structure and integrity of its ecological community. This species has a disproportionately large impact on its environment relative to its abundance. For example, the presence or absence of a keystone species can significantly influence the types and numbers of other species within an ecosystem. The removal of a keystone species can lead to drastic changes in the ecosystem, potentially resulting in its collapse or a significant shift in community structure.

In contrast, the largest species in an ecosystem may not necessarily play an important role in its overall balance; they might simply occupy a niche without affecting other species significantly. Newly introduced invasive species can disrupt ecosystems, but they do not define the role of a keystone species since they can be harmful rather than beneficial to community structure. Lastly, while species at the highest trophic level can be keystone species, not all of them are—some may not have the same integrated influence on their ecosystem compared to those that do serve as keystone species.