In ecology, a population is a group of individual organisms belonging to the same single species which inhabit a specific area. While ecological communities are made up of multiple co-existing species, populations are comprised of multiple co-existing individuals. The chimpanzees of Uganda’s Congo River are a population. So are the chimpanzees of western Tanzania. Though both of these groups belong to the same species, they should be considered separate populations because they do not inhabit the same specific area. When surveying the populations of a targeted area, researchers may be motivated to answer questions such as: what is the average population size? How does the average population size change over time?

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Why Do Populations Grow?

To understand how population sizes vary through time, four relevant factors should be kept in mind: 1) the birth rate of the individual organisms, 2) their death rates 3) the introduction of non native individuals that have migrated from a separate population, 4) the removal of individuals that migrate out of the population being observed. Using these four simple measures enables ecologists to understand how population sizes undergo changes. Populations may have a steady rate of growth, grow exponentially or even grow exponentially up until a certain point. A population’s growth may slowed (or halted completely) by environmental factors, such as the presence of predator species or lack of resources necessary for survival. When a population’s rate of change reaches a predictable rate of change over time, then the population has reached a degree of stability or equilibrium with its environment.

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