The correct answer is "Keystone species."

Keystone species are species within a biological community that play a critical role in maintaining the structure and functioning of the ecosystem. These species have a disproportionate impact on the community relative to their abundance or biomass. The term "keystone" is derived from the architectural concept of a keystone, which is the central stone at the top of an arch that supports and holds all the other stones in place.

Keystone species can have a significant influence on the ecosystem by controlling the population sizes of other species or by modifying the physical environment. Their presence or absence can have cascading effects on the community, affecting species diversity, community composition, and ecosystem stability.

By controlling the abundance of other species or shaping habitat conditions, keystone species help maintain the balance and integrity of the ecosystem. Removing a keystone species from a community can lead to significant disruptions and changes in the community structure, potentially resulting in a loss of biodiversity and ecosystem function.

Therefore, keystone species are important in determining the ability of a large number of other species to persist in the community.