What is a keystone species?

A keystone species is defined as a species that plays a critical role in maintaining the structure and function of an ecosystem. This concept highlights the importance of certain species, which may not necessarily be the most abundant in numbers or biomass, but whose presence or absence can significantly influence the entire ecological community.

These species often affect the types and numbers of various other organisms in the ecosystem, such as predators, prey, and plants. For instance, a keystone predator can help regulate the populations of other species, preventing any one from becoming too dominant and thereby promoting biodiversity. The removal of a keystone species can lead to dramatic changes in the ecosystem, often resulting in a decline in diversity and overall ecosystem health.

In contrast, other options refer to different ecological roles that do not encapsulate the essence of a keystone species. The first option describes pioneer species, which are vital for the initial stages of ecological succession. The third option refers to abundance, which does not imply a critical ecological role. The fourth option describes decomposers, which, while essential, do not fit the definition of a keystone species in the context of ecosystem structure and balance.