POPULATION CONTROLS

Population is simply the total number of individuals of a single kind of creature that occupy a place. Community differs by being the total number of individuals of all kinds of creatures that occupy a place.

However, recall that similar numerical populations may have different dispersion patterns within a place, and that these may be quite significant. Regular dispersion is rare in nature and almost always indicates human control; an example would be a pine plantation. Highly random dispersion often indicates organisms having high mobility and frequent opportunities for transport, such as wind-blown dandelion seeds. Highly clustered dispersion is typical of less mobility, greater habitat selectivity, or more communal organisms; examples would be streambank willows, or a bison herd.

Do note that populations are dynamic; they will change numerically and spatially through time. Large populations may get smaller, or vice versa, and the population may expand, contract, or shift its range.

Very significantly, ecological interdependence may cause the population of one organism to "follow suit" with another. An example is the Everglades kite (Rostrhamus sociabilis), which is strictly dependent on Pomacea snails for food. When snail populations declined due to land modification, so too did the kite. After the imposition of controls over drainage and pesticide use, the snail recovered and the kite numbers soon rose as well.

Dispersion

Population Change

Subpopulations

Change Rates

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Basic Population Change

Population ecology, and its biogeographic extensions, can become extremely quantitative in character. However, one of the most fundamental relationships is a crude relationship to describe or predict population change. Population gains result from either natality (births, germinations, etc.) or immigration (relocations into the population range). Population losses result from mortality (deaths) or emigration (relocations out of the population range). Population change then is simply the net balance of gains less losses; new population is simply the application of population change to the previous population.

In the simple example below, application of the varying values for the four equation terms to the Time A population gives a net population change of +1, raising the population at Time B to 52.