Abstract
Predator communities are changing worldwide: large carnivores are declining while mesocarnivores (medium-sized mammalian predators) are increasing in number and ecological influence. Predator choice of prey is not random and different predators select prey with different characteristics. Changes in predator communities can change predation patterns experienced by prey. Little is known about how mesocarnivore communities influence prey morphology. We used 14 years of mark-recapture data to investigate how mesocarnivore exclusion affected body mass of hispid cotton rats (Sigmodon hispidus). Finding adult male cotton rats were 9% heavier with mesocarnivore exclusion, we developed hypotheses to explain this observation. Greater adult male body mass in exclosures resulted from: (1) a non-significant trend of increased survival of large males, (2) faster juvenile male growth during the fall and a similar non-significant trend among adult males, and (3) spatial partitioning by size among males. Taxa-specific predation rates (i.e., rates of predation by snakes, raptors, or mesocarnivores) did not differ among male body mass classes. Mesocarnivores disproportionately preyed on large females while raptors targeted small females, but female body mass was not influenced by mesocarnivore exclusion. Changes in predator communities can result in multiple small effects that collectively result in large differences in prey morphology.
Highlights
Predation occurs when a predator kills its prey
Because life stages vary in their contributions to population growth and different predators may select prey with different characteristics, shifts in predator communities may result in shifts in prey population dynamics
Behavioural responses to predation risk may result in indirect effects which can be as large or larger than direct effects of predation[12]; shifts in predator communities will likely lead to shifts in the indirect effects of predation experienced by prey populations
Summary
Predation occurs when a predator kills its prey. The simplicity of this definition belies the complexity of the predation process. Effects of mesocarnivores on prey abundance have been well studied[19,20,21,22,23], there has been little investigation into how changes in predator communities influence other aspects of prey such as body mass and growth. Because of the worldwide pervasiveness of shifts in predator communities toward increased mesocarnivore populations, and because hunting modes vary among predator species, such effects may be common. We focused on cotton rats because they serve as important prey for a variety of predators on our study area (i.e., mesocarnivores, snakes, and raptors)[2,25,26] and in the southern United States in general[27,28,29,30], they are the most common prey species on our study site, and because we have long-term mark-recapture and radio-telemetry data available for this species. We examined growth rates, body mass of juveniles at first capture, and size-specific capture probability, survival, and mortality among cotton rats
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