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Wallach AD, Izhaki I, Toms JD, Ripple WJ, Shanas U. What is an apex predator?. Oikos. 2015 Nov
ABSTRACT
Large ‘apex’ predators influence ecosystems in profound ways, by limiting the density of their prey and controlling smaller ‘mesopredators’. The loss of apex predators from much of their range has lead to a global outbreak of mesopredators, a process known as ‘mesopredator release’ that increases predation pressure and diminishes biodiversity. While the classifications apex‐ and meso‐predator are fundamental to current ecological thinking, their definition has remained ambiguous. Trophic cascades theory has shown the importance of predation as a limit to population size for a variety of taxa (top–down control). The largest of predators however are unlikely to be limited in this fashion, and their densities are commonly assumed to be determined by the availability of their prey (bottom–up control). However, bottom–up regulation of apex predators is contradicted by many studies, particularly of non‐hunted populations. We offer an alternative view that apex predators are distinguishable by a capacity to limit their own population densities (self‐regulation). We tested this idea using a set of life‐history traits that could contribute to self‐regulation in the Carnivora, and found that an upper limit body mass of 34 kg (corresponding with an average mass of 13–16 kg) marks a transition between extrinsically‐ and self‐regulated carnivores. Small carnivores share fast reproductive rates and development and higher densities. Large carnivores share slow reproductive rates and development, extended parental care, sparsely populated territories, and a propensity towards infanticide, reproductive suppression, alloparental care and cooperative hunting. We discuss how the expression of traits that contribute to self‐regulation (e.g. reproductive suppression) depends on social stability, and highlight the importance of studying predator–prey dynamics in the absence of predator persecution. Self‐regulation in large carnivores may ensure that the largest and the fiercest do not overexploit their resources.
By Janet Fang
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.