A keystone species is a species that has a disproportionately large effect on its environment relative to its biomass or abundance. The presence or absence of a keystone species can significantly influence the structure and diversity of an ecosystem. These species play crucial roles in maintaining the ecological balance by regulating populations of other species and facilitating species diversity.
One classic example of a keystone species is the sea otter (Enhydra lutris). Sea otters consume sea urchins, which are herbivores that graze on kelp forests. When sea otters are present, they help control the sea urchin population, allowing kelp forests to thrive. If sea otters are removed from the ecosystem, unchecked sea urchin populations can lead to overgrazing of kelp, resulting in the collapse of the entire kelp ecosystem and the loss of numerous species that depend on it for habitat and food.