The number of individuals in an area of a specific size.

• A. Carrying capacity
• B. Population density
• C. Biomass
• D. Habitat area

Answer: (B)

Population density is the number of individuals per unit area, which is exactly what the phrase “the number of individuals in an area of a specific size” measures. It’s found by counting organisms in a defined area and dividing by that area, giving units like individuals per square kilometer. This metric helps ecologists compare how crowded different habitats are and understand patterns of resource use, interactions, and potential disease spread. The other terms describe different ideas: carrying capacity is the maximum population the environment can sustain over time; biomass is the total mass of living organisms in an area; habitat area refers to the size of the space itself, not how many individuals occupy it.