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3.2.1: Population Dispersion

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    The dispersion pattern (distribution pattern) of a population describes the arrangement of individuals within a habitat at a particular point in time, and broad categories of patterns are used to describe them. The three dispersion patterns are clumped, random, and uniform (figure \(\PageIndex{a}\)).

    Examples of random, clumped, and uniform population distributions with dandelions, elephants, and penguins, respectively.
    Figure \(\PageIndex{a}\): Species may have a random, clumped, or uniform distribution. Plants such as (a) dandelions with wind-dispersed seeds tend to be randomly distributed (represented by dots in no particular pattern). Animals such as (b) elephants that travel in groups exhibit a clumped distribution (represented by dots clustered together). Territorial birds such as (c) penguins tend to have a uniform distribution (represented by dots evenly spaced from each other). (credit a: modification of work by Rosendahl; credit b: modification of work by Rebecca Wood; credit c: modification of work by Ben Tubby)

    Individuals that are grouped into patches have a clumped distribution, or aggregated distribution. This can occur if resources are distributed unequally; for example, pipevine swallowtail caterpillars would be clumped in areas with their host plant, California pipevine. Clumped distribution may also reflect the locations of suitable microhabitats, such as an herbaceous (non-woody) plant species that only grows in the shade clustering under trees. Plants that drop their seeds straight to the ground, such as oak trees, may also have this distribution. Finally, social behavior in animals results in a clumped distribution, such as wolves hunting in a pack, a herd of elephants, or a school of fish traveling together for safety.

    Populations that have a random distribution are not arranged in any particular pattern. Some individuals may be close together while others may be far apart. An example of random distribution occurs with dandelion and other plants that have wind-dispersed seeds that germinate wherever they happen to fall in favorable environments.

    Individuals that are equally spaced in the environment have a uniform distribution. Saguaro cacti are evenly spaced due to limited resources in the desert. (There is not sufficient water to support two large cacti side-by-side.) Uniform distributions can result from interference competition, when individuals take pre-emptive measures to avoid comeptition for resources. For example, some plants that secrete substances inhibiting the growth of nearby individuals (such as the release of toxic chemicals by sage plants), a phenomenon called allelopathy. Another example of interference competition occurs in territorial animal species, such as penguins that maintain a defined territory for nesting. The territorial defensive behaviors of each individual create a regular pattern of distribution of similar-sized territories and individuals within those territories. Thus, the distribution of the individuals within a population provides more information about how they interact with each other than does a simple density measurement (see Population Size and Density).


    Modified by Melissa Ha from Population Demographics and Dynamics from Environmental Biology by Matthew R. Fisher (CC-BY)

    This page titled 3.2.1: Population Dispersion is shared under a CC BY-NC license and was authored, remixed, and/or curated by Melissa Ha and Rachel Schleiger (ASCCC Open Educational Resources Initiative) .