What term defines a species whose loss could collapse the ecosystem?

• A. Endemic species
• B. Keystone species
• C. Indicator species
• D. Invasive species

Answer: (B)

Keystone species have a disproportionate impact on ecosystem structure relative to their abundance. Their effects help maintain the balance of the community, so when they are removed, the interactions among other species unravel and the ecosystem can shift dramatically or even collapse. This happens because many keystone species are central to key processes—predation that keeps herbivore populations in check, habitat modification that creates living space or resources for others, or engineering of physical environments that support diverse communities. Without them, trophic cascades or habitat loss spread through the system, leading to large, often cascading changes in species composition and ecosystem function.

Endemic species, while important and often vulnerable, are defined by their limited geographic range, not by the size of their ecological role. Indicator species are used to signal the health of an environment, not to describe a species whose loss would destabilize the whole system. Invasive species cause disruption because of their non-native status and aggressive interactions, but that’s about their origin and impact, not about a natural role that would cause collapse if removed.