Population Size and Density

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Graph plots log density in kilometers squared versus log body mass in grams. The values are inversely proportional, so that density decreases linearly with increasing body mass.
Australian mammals show a typical inverse relationship between population density and body size. Source: OpenStax Biology 2e

OpenStax Biology 2e

The study of any population usually begins by determining how many individuals of a particular species exist, and how closely associated they are with each other. Within a particular habitat, a population can be characterized by its population size (N), the total number of individuals, and its population density, the number of individuals within a specific area or volume. Population size and density are the two main characteristics used to describe and understand populations. For example, populations with more individuals may be more stable than smaller populations based on their genetic variability, and thus their potential to adapt to the environment. Alternatively, a member of a population with low population density (more spread out in the habitat), might have more difficulty finding a mate to reproduce compared to a population of higher density. As is shown in the image above, smaller organisms tend to be more densely distributed than larger organisms.


Clark, M., Douglas, M., Choi, J. Biology 2e. Houston, Texas: OpenStax. Access for free at: https://openstax.org/details/books/biology-2e


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