Abstract
The presence of large carnivores can affect lower trophic levels by suppressing mesocarnivores and reducing their impacts on prey. The mesopredator release hypothesis therefore predicts prey abundance will be higher where large carnivores are present, but this prediction assumes limited dietary overlap between large and mesocarnivores. Where dietary overlap is high, e.g., among omnivorous carnivore species, or where prey are relatively easily accessible, the potential exists for large and mesocarnivores to have redundant impacts on prey, though this possibility has not been explored. The intertidal community represents a potentially important but poorly studied resource for coastal carnivore populations, and one for which dietary overlap between carnivores may be high. To evaluate usage of the intertidal community by coastal carnivores and the potential for redundancy between large and mesocarnivores, we surveyed (i) intertidal prey abundance (crabs and fish) and (ii) the abundance and activity of large carnivores (predominantly black bears) and mesocarnivores (raccoons and mink) in an area with an intact carnivore community in coastal British Columbia, Canada. Overall carnivore activity was strongly related to intertidal prey availability. Notably, this relationship was not contingent on carnivore species identity, suggestive of redundancy–high intertidal prey availability was associated with either greater large carnivore activity or greater mesocarnivore activity. We then compared intertidal prey abundances in this intact system, in which bears dominate, with those in a nearby system where bears and other large carnivores have been extirpated, and raccoons are the primary intertidal predator. We found significant similarities in intertidal species abundances, providing additional evidence for redundancy between large (bear) and mesocarnivore (raccoon) impacts on intertidal prey. Taken together, our results indicate that intertidal prey shape habitat use and competition among coastal carnivores, and raise the interesting possibility of redundancy between mesocarnivores and large carnivores in their role as intertidal top predators.
Highlights
The structure of mammalian carnivore communities can be a major determinant of species abundance across food webs
The potential for redundancy has not been considered in studies of mammalian mesopredator release, which, as noted above, typically focus on large carnivore and mesocarnivore species with limited dietary overlap [3,6,7,11], and often detect substantial differences in the prey community in the presence and absence of large carnivores (e.g., [3,4])
We found that the composition of the mammalian carnivore community in coastal habitats of Clayoquot was determined both by interactions between carnivore species and by the availability of intertidal prey, indicating that intertidal prey abundance shapes habitat use and competition among this guild of terrestrial predators
Summary
The structure of mammalian carnivore communities (i.e., the relative abundance of large carnivores and mesocarnivores) can be a major determinant of species abundance across food webs. When large carnivores and mesocarnivores utilize the same resources, little change in the shared prey community may be expected if the potential exists for released mesocarnivores to assume the functional role of an extirpated large carnivore, e.g., through increased abundance and/or per capita impacts on prey [22,23,24], as has been demonstrated among invertebrate predators [19]. This may be likely when the carnivore community contains highly omnivorous large carnivores and mesocarnivores with substantial dietary overlap [25,26]
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