What is a keystone species?

A keystone species plays a crucial role in maintaining the structure and integrity of an ecosystem. The presence and activities of a keystone species have a disproportionately large impact on its environment relative to its abundance. For instance, these species can influence the populations of other organisms and the overall health of the ecosystem. By controlling the populations of prey species or competing species, a keystone species helps to ensure biodiversity and stability within the ecosystem.

In contrast, the other options do not accurately represent the unique role of a keystone species. A species with no effect on its ecosystem lacks significance and would not be classified as a keystone species. Similarly, while a species that competes for resources may influence its ecosystem, it doesn't capture the specific pivotal role associated with keystone species. Lastly, adaptability to changing environments describes a species' ability to survive under varying conditions but does not directly relate to the structural role that infers a keystone status.