Which best describes a keystone species?

A keystone species is one that has a disproportionately large impact on its environment relative to its abundance. It plays a critical role in maintaining the structure of an ecological community, influencing the types and numbers of various species in an ecosystem.

In the context of the options given, the definition of a dominant predator aligns closely with the characteristics of a keystone species. Such species often regulate the populations of prey species, which in turn helps maintain a balance within the ecosystem. For example, the presence of a top predator can control the populations of herbivores, preventing overgrazing and allowing vegetation to thrive, which supports a diverse array of other organisms.

This dynamic illustrates how the health and stability of an ecosystem can rely heavily on specific species that regulate biological communities, making the understanding of keystone species crucial for conservation efforts.