What role do keystone species play in an ecosystem?

Keystone species play a crucial role in maintaining the structure and integrity of an ecosystem, and their impact on the environment is disproportionately large compared to their abundance. This means that even if keystone species are relatively few in number, their presence or absence can significantly influence the populations and activities of numerous other species within that ecosystem.

For instance, the removal of a keystone species can lead to dramatic shifts in the community composition and overall stability of an ecosystem. This might manifest as population explosions of certain species that would otherwise be kept in check or a decline in biodiversity. Classic examples of keystone species include certain predator species that help regulate prey populations, thereby promoting a more diverse range of organisms within their habitat.

In contrast, the other options do not accurately capture the essence of keystone species. For example, a minor impact on the environment does not align with the definition of a keystone species, as their influence is significant. While some keystone species may be top predators, not all keystone species fit this category, and being most numerous is also not a characteristic of keystone species, as their defining trait is the extent of their ecological impact rather than their abundance.