What is a keystone species?

A keystone species is defined as a species that has a disproportionate effect on its environment relative to its abundance. This means that the presence or absence of a keystone species can significantly influence the structure and function of an ecosystem. For instance, removing a keystone species from an ecosystem can lead to dramatic changes, such as a collapse in certain populations or changes in vegetation structure, which can affect numerous other species.

These species often fulfill roles that are critical for maintaining the ecological balance; examples include predators that regulate prey populations, or species that alter the environment, such as beavers that create wetlands. The concept emphasizes the interconnectedness of species within an ecosystem and highlights the importance of certain species in maintaining ecological integrity.

In contrast, the other options describe characteristics that do not align with the specific ecological role of a keystone species. For example, while the size of a species, its conservation status, or migratory behaviors can be significant attributes in other contexts, they do not define the critical influence a keystone species has on its environment.