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Simply by reproducing, any organism might take over the world. Population ecologists employ a variety of mathematical tools to model population dynamics.

Two models, depending on population size and required resources, can be used to characterize population expansion. Exponential growth and logistic growth are the two types of growth.

A population will increase exponentially if given unlimited resources such as food and water, land if needed, wetness, oxygen, and other environmental conditions. As a population grows larger, exponential growth occurs, substantially increasing the pace of expansion.

There are no such phenomena as logical growth curves and experimental growth curves.

When resources are scarce, the population's growth curve is known as the logistic growth curve. Because resources become finite at some point, such a growth curve is evident in practically all sorts of populations.