Summary of Chapter Concepts

The distribution of populations is limited to ecologically suitable habitats. The range of suitable abiotic conditions where individuals can persist represents the fundamental niche of a species. The subset of conditions where a species actually persists due to biotic interactions is known as the realized niche. With an understanding of the realized niche, ecologists can use ecological niche modeling to predict the areas in which a species could persist if it were to be introduced.

Population distributions have five important characteristics. The geographic range of a population is a measure of the total area it covers. The abundance of a population is the total number of individuals that exist within a defined area. The density of a population is the number of individuals per unit area or volume. Dispersion of a population describes the spacing of individuals with respect to one another. Dispersal is the movement of individuals from one area to another.

The distribution properties of populations can be estimated. These properties are typically measured by using a variety of survey techniques including area- and volume-based studies, line-transect studies, and mark-recapture studies.

Population abundance and density are related to geographic range and adult body size. There is generally a positive relationship between the abundance of a population and the size of its geographic range, although many other biotic and abiotic factors play a role in determining geographic range size. There is commonly a negative relationship between adult body size and the density of a population because larger individuals require more energy.

Dispersal is essential to colonizing new areas. Many populations do not inhabit suitable habitats because they are dispersal limited. One of the key ways to facilitate dispersal is through the creation of habitat corridors.

Many populations live in distinct patches of habitat. The ideal free distribution makes predictions about how individuals should distribute themselves if they were to equalize the per capita benefits, although this is rarely observed in nature due to the importance of other factors such as predators and territoriality. Ecologists have used three types of population structure models: the metapopulation model, the source–sink model, and the landscape model.

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