What characterizes a keystone species?

A keystone species is characterized by its significant and disproportionate impact on the structure and dynamics of its ecosystem, despite not necessarily being the most abundant species within that ecosystem. This means that the presence or absence of a keystone species can greatly influence population sizes of other species and the overall biodiversity.

For instance, a keystone species may help maintain the balance within an ecosystem by preying on various organisms, which in turn prevents any one species from dominating the ecosystem. The classic example is the sea otter, which preys on sea urchins; if otters are removed from the environment, sea urchin populations can explode, leading to the destruction of kelp forests, which provide habitat for numerous other species.

The other choices describe characteristics that do not capture the essence of what defines a keystone species. A species that migrates seasonally does not inherently impact its ecosystem in the way a keystone species does. Similarly, the abundance of a species in an ecosystem does not determine its keystone status; many keystone species are not the most numerous. Lastly, being at the top of the food chain may imply a significant role in the ecosystem, but it does not guarantee that the species is a keystone species, as