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How do predators disease organisms and competitors limit the abundance of a species?

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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, predators, disease, and competitors act as density-dependent factors that regulate the abundance of a species by exerting greater influence as population density increases.12

Predators: Predators, grazers, and parasites help maintain smaller population sizes by consuming individuals within a community. By hunting prey, predators can limit the number of individuals in an area and even trigger avoidance behaviors that influence the activity of other species. When species are introduced to new environments without their natural enemies, they often experience explosive population growth, demonstrating the regulatory role of predation.34
Disease: Infectious diseases spread more efficiently in dense populations where individuals are in close proximity. Overcrowding often facilitates higher transmission rates, which can lead to increased mortality and a subsequent decline in population size.125
Competitors: Competition for critical resources—such as food, water, and nesting sites—intensifies as population density rises. This competition limits the proportion of the population that can survive and reproduce. Interspecific competition can further restrict a species' abundance, sometimes leading to the exclusion of one species by another.1267