Which of the following best describes a keystone species in a community?

• A. A species that has a disproportionately large effect on its community relative to its abundance.
• B. A species that is the most abundant in the community.
• C. A species that occupies the largest area in the community.
• D. A species that is always at the top of the food chain.

Answer: (A)

Verified step by step guidance

1. Understand the concept of a keystone species: A keystone species is one that has a disproportionately large impact on its ecosystem relative to its abundance. This means that even if the species is not the most abundant, its role is critical in maintaining the structure and balance of the community.
2. Eliminate the incorrect options: A keystone species is not defined by being the most abundant species in the community. Abundance refers to the number of individuals of a species, but keystone species are impactful regardless of their population size.
3. Consider the role of area: A keystone species is not determined by the amount of area it occupies. The physical space a species occupies does not necessarily correlate with its ecological importance.
4. Evaluate the food chain position: While some keystone species may be at the top of the food chain, this is not a defining characteristic. Keystone species can exist at various trophic levels, including predators, prey, or even ecosystem engineers.
5. Select the correct description: The best description of a keystone species is 'A species that has a disproportionately large effect on its community relative to its abundance.' This definition highlights the ecological importance of the species rather than its abundance, area, or position in the food chain.