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Janet Fang 02/03/2015, 02:01

Unlike small mammals who multiply like bunnies or some predators who’s boom or bust depends on said bunnies, large carnivores like lions and wolves keep their own numbers in check. According to a new work published in Oikos last week, population control is what distinguishes “apex predators” from the rest. 

Researchers have traditionally assumed that the densities of the largest of predators are determined by the availability of their prey supply, but recent studies seem to contradict a bottom-up control. And now, an international team led by Arian Wallach from Charles Darwin University proposes an alternate view: Apex predators naturally have the capacity to limit their own population densities—or self-regulate—helping to keep their ecosystems in balance.

The team tested their idea using a set of life-history traits that might contribute to self-regulation in mammalian carnivores, such as birth rate and investments by parents. They gathered research on more than a hundred species, Science reports, from skunks and stoats to polar bears, panthers, and wolves living in Yosemite. They found that an average weight of 13 to 16 kilograms (29 to 35 lbs) marks a transition between self-regulated carnivores and those that are regulated by external factors.

Small carnivores have fast rates of development and reproduction, as well as higher densities. Large carnivores, on the other hand, have slow reproductive rates and development, extended parental care, sparsely populated territories, and a natural tendency towards infanticide, reproductive suppression, and cooperative hunting, the authors write. 

About half of these large carnivores control the numbers within their group by only letting certain members breed, Science explains. Many of the bigger predators are known to have complex social systems: Dominant female wolves and hyenas, for example, kill the pups of subordinates, and in many large carnivores, the group ends up raising the alpha female’s (or pair’s) pups together. Self-regulation in large carnivores, they conclude, likely ensures that the largest and fiercest never overexploit their resources.

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