Which of the following describes population size?

Population size refers specifically to the number of individual organisms within a defined area at a given time. This metric is crucial for understanding the health and viability of a population. When considering option B, it accurately describes population size as it emphasizes the count of individuals that contribute to the gene pool.

The gene pool is the complete set of genetic information within a population, and it is directly related to the actual number of individuals present. A larger population size typically results in a broader gene pool, enhancing genetic diversity and promoting resilience to environmental changes.

The other choices address related but distinct concepts. The total area occupied by a population pertains to habitat range and distribution rather than the number of individuals. The average lifespan looks at longevity rather than quantity, while genetic diversity focuses on the variation of genes within the population, not the number of individuals themselves. Understanding population size is fundamental in ecology, as it affects resource availability, reproductive success, and overall survival of the species.