Understanding populations involves two key metrics: population size and population density. Population size, denoted by the variable n, refers to the total number of individual organisms within a population. This metric is simply a count and does not take into account the area that the population occupies, making it less useful for comparing populations across different regions with varying sizes.

In contrast, population density provides a more nuanced understanding by relating the population size to a defined unit of area or volume. This metric is calculated as:

Population Density = \(\frac{n}{A}\)

where A represents the area. By considering the area, population density reveals how crowded a population is, allowing for standardized comparisons between populations in different regions, regardless of their size.

For example, consider three populations of black-tailed deer on islands of different sizes. Although the population size on each island is the same, the population densities vary significantly. The small island exhibits a high population density, indicating a crowded environment, while the large island shows a low population density, suggesting a more spacious habitat. The medium-sized island falls somewhere in between. This illustrates the importance of using both metrics to gain a comprehensive understanding of population dynamics.