What does the term "keystone species" refer to?

The term "keystone species" refers to a species that has a disproportionately large impact on its environment, relative to its abundance. Keystone species play a crucial role in maintaining the structure of an ecological community, influencing the diversity and population dynamics of other species within that ecosystem. Their activities can enhance biodiversity, control populations of other species, and stabilize the environment.

For example, in a coastal ecosystem, a predator like sea otters can keep sea urchin populations in check. If otters are removed, sea urchins may proliferate and overgraze kelp forests, leading to a significant decline in overall biodiversity. Thus, the presence or absence of a keystone species can dramatically alter the ecosystem, making them vital to ecological balance.

This concept differs from other choices where dominance in numbers, risk of extinction, or habitat provision does not encompass the critical influence that the species has on its ecological community structure. By enhancing the understanding of keystone species, it becomes clear how intricately linked various organisms are within their environments and highlights the complexity and interdependence of ecosystems.