In an ecosystem, what is the main function of keystone species?

The primary role of keystone species in an ecosystem is to significantly influence the dynamics and diversity of other species within that community. Keystone species maintain the structure of the ecosystem and have a disproportionately large impact on their environment relative to their abundance. This can occur through various mechanisms, such as predation, competition, or providing essential resources.

For example, a predator that preys on a particular herbivore can help regulate that herbivore's population, preventing overgrazing and allowing plant diversity to thrive. Similarly, a species that provides a critical habitat or resource can enable other organisms to survive and thrive in that ecosystem. In this way, keystone species help to maintain balance and promote biodiversity, highlighting their essential role in ecological stability.

In contrast, the other options focus on more narrow functions, such as being prey or competing for resources, which do not encompass the broader ecological impact that defines the keystone species concept. Hence, the understanding of keystone species revolves around their influence on the ecological community rather than solely on roles like competition or providing habitat.