Define a population and a community in ecological terms.

• A. A population includes all species in a region.
• B. A population is the total number of individuals in a region.
• C. A population is all individuals of one species in a region; a community is all populations of different species in an area.
• D. A population describes a group of ecosystems.

Answer: (C)

Distinguishing populations from communities: a population is all individuals of a single species within a defined area. This focuses on one species and helps us study its size, growth, and how it interacts with its immediate environment. A community, on the other hand, includes all the living organisms of all species in that area, with the interactions among them—predation, competition, mutualism, and other relationships—that shape how those species coexist.

For example, in a pond, the population of bluegill would be every bluegill fish in that pond. The community would include bluegill, frogs, water insects, aquatic plants, algae, and all the other species living there, plus how they influence one another.

The other descriptions miss that distinction: describing all species in a region refers to a community, not a single-species population; counting all individuals in a region without specifying species isn’t capturing the population concept; and a group of ecosystems goes beyond population or community to a larger level like an ecosystem or biome.