Predation and Wildlife Population Regulation

Predation is an interaction in which one organism, the predator, kills and consumes another, the prey. It contributes to population regulation by adding mortality to prey populations, while prey availability influences predator survival and reproduction. Regulation means limiting population growth and fluctuations, not maintaining a permanently fixed population size.

Direct regulation and predator-prey feedback

Predation links the abundance of consumers to their food supply. This can create negative feedback, through which an increase in a population generates pressures that subsequently limit its growth.

• When prey become more abundant, predators may encounter and consume them more frequently, increasing predation pressure.
• Greater food availability can improve predator survival and reproduction, although an increase in predator numbers usually takes time.
• As prey decline, food scarcity can reduce predator reproduction or survival, or cause predators to switch to other prey.
• These linked responses can produce predator-prey fluctuations, but regular cycles are not a universal feature of natural ecosystems.

Indirect effects on communities and food webs

Predators influence more than the number of animals they consume. Their effects can extend across trophic levels, changing the abundance and interactions of other organisms.

• By limiting herbivore abundance or changing where herbivores feed, predators can reduce grazing or browsing pressure on vegetation; such effects can form a trophic cascade.
• Predators can help maintain species diversity by preventing a competitively dominant prey species from excluding other species.
• Predation transfers energy from prey to predators and forms an important link in food chains and food webs.

Limits to regulation and conservation implications

Predation operates alongside food availability, competition, disease and habitat conditions. Its importance therefore varies among species, habitats and seasons.

• Predators do not necessarily control every prey population; prey refuges, alternative foods and environmental variation can weaken their regulatory influence.
• Predation need not always cause an equal reduction in population growth: some individuals killed might otherwise have died from starvation, disease or other causes.
• Removing predators can release some prey populations from control and alter community structure, but the outcome depends on the wider food web.
• Conservation management should distinguish the normal ecological role of predation from its effects on a small, threatened population, where additional mortality may hinder recovery.