Conspecific density affects predator‐induced prey phenotypic plasticity

Abstract

Abstract. The risk-assessment hypothesis (R-AH) states that prey must consider conspecific density and not simply the concentration of predation cues to evaluate actual predation risk. However, little is known about whether the R-AH might serve to predict predator-inducible plastic responses involving different prey phenotypes. We approached this question through an experiment in outdoor mesocosms, manipulating predation risk (with caged predators) and prey conspecific density to test the importance of R-AH for the expression of predator-induced morphological and behavioral phenotypes. We found behavioral (swimming activity) and morphological (tail width and tail muscle depth) responses of bullfrog tadpoles (Lithobates catesbeianus) to be affected by chemical predation cues. However, only the morphological phenotype responded to the predation-risk:conspecific-density interaction. The width of the tail and the muscle depth of tadpoles were significantly greater when individuals were exposed to predators. However, this effect was not significant in treatments with high prey density in an experimental setup that minimized intraspecific competition. We interpret the differences found among the responses of the phenotypes in terms of the effects of three factors: the potential costs related to each phenotype expression, how these phenotypes are affected by environmental conditions and the immediate response of the phenotypes to actual and perceived prey risk. Our results shed light on the fact that prey individuals use information about population density to estimate actual predation risk from chemical cues. However, different traits are differentially affected, suggesting that trade-off mechanisms associated with the costs of the expression in terms of anti-predator defenses may interfere with the predictions of R-AH for multiple prey phenotypes.

Interactive effects of predation risk and conspecific density on the nutrient stoichiometry of prey

“…This evidence supports many previous observations of additional responses by prey, beyond physiological stress, in the presence of predators (Preisser and Bolnick 2008). Prey might increase refuge use (Lima and Dill 1990), produce spines (Tollrian 1995), or change their shape (Guariento et al 2015) in the presence of predators, which in turn can affect body nutrient content and recycling patterns (Costello and Michel 2013;Dalton and Flecker 2014). Using guppies as a model system, Dalton and Flecker (2014) reported that guppies tended to increase N assimilation efficiency and N content as an adaptive response to a reduced quantity and quality of resources in refuges, thus sparing high-quality molecules (i.e., proteins) from catabolism.…”

Individual responses to novel predation risk and the emergence of a landscape of fear

“…If, however, risk was distributed homogeneously within individual home ranges it was likely more difficult for individuals to adjust their space-use tactics in response to risk and may have made it more difficult for us to detect a functional response. Individual differences in the response to risk may have depended on individual experience, or other non-exclusive factors, such as propensity to take risk (Ciuti et al 2012), proximity to refuge (e.g., Tolon et al 2009), ability to move home range (Padié et al 2015), and differences in age (Lone et al 2015), body condition (McNamara 1997), and local density (Guariento et al 2015).…”

Effects of lions on behaviour and endocrine stress in plains zebras

“…We find such an explanation unlikely. Second, prey density has been observed to influence how prey responds to predation risk (Guariento, Carneiro, Esteves, Jorge, & Caliman, ). In our study, there was lower zebra density in the reserve containing lions than in the reserve that did not.…”