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How does carrying capacity limit population growth?

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Common wildebeest — population ecology A herd of common wildebeest (*Connochaetes taurinus*) migrating across a dusty savanna in Africa. The animal is a keystone species (i.e., a species with a disproportionately large effect on its biological community) in plains and acacia savanna ecosystems from southeastern Africa to central Kenya.

In population ecology, carrying capacity is the average population size or density that an environment can sustain for a specific species. It acts as a limit on growth because, as a population approaches this threshold, the availability of essential resources—such as food, water, and shelter—becomes insufficient to support further expansion.1

When a population exceeds its carrying capacity, its numbers tend to decrease due to resource shortages, which can lead to environmental deterioration or a population crash. This process is governed by density-dependent factors, where competition for limited resources intensifies as the number of individuals per unit area increases.123

This self-limiting growth is often modeled by the logistic function, which produces an S-shaped curve. In this model, growth is initially rapid but slows as the population approaches the carrying capacity ( $L$ ), eventually leveling off as the environment reaches a point of stability. Ultimately, competition within a species for survival needs serves as a primary mechanism for regulating population numbers within a habitat.45