Disentangling the effects of predation and density on resource use among and within populations




Marques, Piatã
Frauendorf, Therese
Warbanski, Misha
Zandonà, Eugenia
Phillip, Dawn
El-Sabaawi, Rana

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The effect of predation on prey is often studied at the population level, with little regard to the effects within the prey population. In this paper we evaluate intrapopulation variation in resource use and gut length of the guppy, Poecilia reticulata, under different predation regime. We specifically test whether predation regime, food availability or population density drive resource use. We also evaluate if differences in resource use and gut length emerge on contemporary timescales after guppies are released from predators. We show that resource use has a bimodal distribution, suggesting that guppy populations have two ecologically distinct resource-use phenotypes (carnivorous and detritivorous/algivorous). These phenotypes exist in both ancestral and derived populations and have different gut length: carnivorous guppies have shorter guts than detritivorous/algivorous. The frequency of the carnivorous phenotypes is related to guppy density. A shift in resource use distribution (towards a detritivorous/algivorous phenotype) is established after a few generations (15-18) post-predator release. Typically, bimodality in resource use is associated with stark differences in morphology and feeding habitats. Our study shows that it can also occur in a much more subtle way, being affected by population density, which raise the question that intrapopulation bimodal variation might be a widespread phenomenon.