Which type of species plays a crucial role in maintaining the structure of an ecosystem?

Keystone species are critical to the maintenance of ecological community structure. Their presence and activities significantly influence the types and numbers of species within an ecosystem, ensuring a balance among various organisms. For example, a predator might control the population of herbivores, which in turn maintains plant diversity. If keystone species are removed, it can lead to dramatic shifts and can potentially collapse the ecosystem—highlighting their essential role.

In contrast, invasive species can disrupt ecosystems, pioneer species help initiate ecological succession but do not typically maintain balance on their own, and endemic species are adapted to a specific region but don't play the same multifaceted role in ecological stability. Thus, the role of keystone species is integral for nurturing and sustaining ecological integrity.