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How do density-dependent factors affect population size?
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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, density-dependent factors are forces that influence the size of a population in response to its density—the number of individuals per unit area. These factors act as regulatory mechanisms that help maintain population density within a specific range.1
As population density increases, these factors exert a greater influence, typically slowing growth or increasing mortality. Common examples include:12
- Competition: As individuals become more crowded, competition for limited resources such as food, water, and nesting sites intensifies, reducing the resources available to each member.12
- Disease: Pathogens often spread more rapidly in dense populations where individuals are in frequent close contact.1
- Predation: High prey density can lead to increased predation rates, which in turn affects the growth dynamics of both predator and prey populations.23
Conversely, when density decreases, the impact of these factors weakens, allowing for potential population recovery. Ultimately, these interactions help determine an environment's carrying capacity, the upper limit of individuals an environment can sustain.12