Abstract
As humans continue to alter the species composition and size structure of marine food webs, it is critical to understand size-dependent effects of predators on prey. Yet, how shifts in predator body size mediate the effect of predators is understudied in tropical marine ecosystems, where anthropogenic harvest has indirectly increased the density and size of small-bodied predators. Here, we combine field surveys and a laboratory feeding experiment in coral reef fish communities to show that small and large predators of the same species can have similar effects. Specifically, surveys show that the presence of a small predator (Paracirrhites arcatus) was correlated with lower chances of prey fish presence, but these correlations were independent of predator size. Experimental trials corroborated the size-independent effect of the predator; attack rates were indistinguishable between small and large predators, suggesting relatively even effects of hawkfish in various size classes on the same type of prey. Our results indicate that the effects of small predators on coral reefs can be size-independent, suggesting that variation in predator size-structure alone may not always affect the functional role of these predators.
Highlights
Body size is a fundamental factor governing the effects of predators on prey [1]
We found that hawkfish occurrence was negatively correlated to the density of their prey species, but that these effects of small 6 versus large hawkfish were statistically indistinguishable
The size-independent nature of both direct and indirect effects of hawkfish on their prey suggests that natural variation in predator size may not modify the effects of these small predators on their prey
Summary
Body size is a fundamental factor governing the effects of predators on prey [1]. Larger predators tend to have higher consumption rates due to their larger mouths and experience [2], 2016 The Authors. Experiments have demonstrated that predation is a key ecological force driving the population dynamics, biodiversity and community assembly of coral reef fishes [10,11,12], highlighting how the role of predation can shift with predator identity [13] and density [14]. The role of intraspecific variation in predator body size in mediating the effects of predators on prey remains understudied Disentangling such size-dependent effects of predators on prey in coral reef fishes is critical to improving our understanding of how natural and anthropogenically induced variation in predator size affects the dynamics, structure and stability of coral reef communities. We combine field observations and a laboratory experiment to quantify how intraspecific variation in the body size of a coral reef mesopredator (Parracirrhites arcatus) mediates its effect on prey fish communities in Moorea, French Polynesia. Body size has limited influence on the effects of P. arcatus on prey, we predicted no difference between small and large P. arcatus in both the field study (occupation of coral heads by prey fishes) and the laboratory study (survival of prey in tanks)
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