What is a keystone species?

A keystone species is defined as a species that has an unusually large effect on its ecosystem relative to its abundance. This means that the presence or absence of a keystone species can significantly alter the structure and health of the ecosystem. For example, in some ecosystems, certain predators regulate the populations of herbivores, which in turn affect vegetation and the overall landscape. Without the keystone species, the ecosystem could become unbalanced, leading to a decline in biodiversity and stability. The concept emphasizes the interconnectedness within an ecosystem, highlighting how the role of certain species can be crucial in maintaining the ecological balance.

The other options describe different ecological roles or characteristics that do not capture the essence of what a keystone species is. A highly adaptable species or the most abundant species may play important roles in their environments, but they do not necessarily have the outsized impact on ecosystem dynamics that defines keystone species. Similarly, species with short lifespans might influence stability, but their short duration does not inherently classify them as keystone species if they do not have the significant, disproportionate role associated with the term.