Large carnivores are increasingly viewed as integral components of terrestrial ecosystems due to their strong cascading effects on other species, including mesopredators. Interactions among carnivores have been examined largely within the context of intraguild predation theory, in which large carnivores suppress mesopredators. However, emerging research highlights the importance of positive interactions, such as facilitation, in structuring communities. Large carnivores provide substantial food subsidies to mesopredators in the form of carrion. The cascading effects of intraguild facilitation could rival the cascading effects of suppression, but the relative importance of these opposing interaction pathways remains unknown because they have been examined separately. We synthesized recent empirical studies examining intraguild predation, carrion provisioning, and scavenging among carnivores to determine the relative strength of these pathways in ecosystems around the world.
We extracted data from 217 studies conducted on 6 continents. Large carnivores were responsible for 30% of collared mesopredator deaths in areas with sympatric large carnivores (n = 63 studies). Rates of intraguild killing were highest among pairs with intermediate body size ratios, peaking when the large carnivore was three times larger than the mesopredator (e.g, wolf-coyote). Large carnivores provided an average of 1,912 kg of abandoned carrion per individual per year, or 163.5 kg/km2 when adjusted for large carnivore density. In contrast, the average standing crop of live small prey (lagomorphs, voles, and mice) reported among 33 studies was 57 kg/km2. Carrion comprised a larger proportion of the diet for larger mesopredator species (R2 = 0.56, n = 16 species). This synthesis reveals that large carnivores exert strong positive and negative forces on mesopredators, and body size is a key factor mediating interaction strengths. Large carnivores may increase the stability of mesopredator populations, because facilitation during lean times and suppression during rich times should dampen the numerical response of mesopredators to fluctuations in small prey abundance. However, reliance on large carnivores to control mesopredators may fail when conditions lead to intraguild facilitation rather than suppression.