Responses of prey animals to odor cues from two predator species across interspecific size gradients

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Prey animals must perform a balancing act between foraging for food, finding mates, and seeking shelter, while avoiding predation (Sih, 1980). If prey animals are overly cautious and respond to every predator cue, then they will expend unnecessary energy on predator avoidance behaviors (Brown, 1999). Such an aversion to risk will also severely limit the prey’s access to resources (Kats & Dill, 1998). If prey do not respond to predator cues, the probability that they will encounter a predator is increased. However, prey that risk ignoring predator cues have more time to acquire resources and can utilize more of their habitat (Lima & Dill, 1990). Neither extreme case is commonly observed in natural systems because prey use factors like predator proximity, species, relative size, and diet to only respond to the most threatening predators. Information relevant to all these factors can be extracted from the odor cues released by predators. Prey animals can differentiate the odors of predators from those of non-threatening species, recognize distinct predator species, and respond accordingly to predators with different hunting strategies (Gherardi et al., 2011). Odor cues also contain information about the predator’s diet. Predators that have recently consumed conspecific prey are perceived as greater threats than those that have not (Chivers and Mirza, 2001). Odor cues can provide information about the size of the predator as well. An individual prey animal may respond differently to a large or small predator of the same species (Apfelbach et al., 2005). Once prey have a detailed assessment of the threat posed by a predator, they can weigh the value of the resource against the risk required to obtain it. Currently, it is unknown how prey combine information about predator species and predator size relative to individual prey to assess risk and make resource use decisions. Parsons et al. (2018) specifically calls for studies which address this gap in knowledge by quantifying the food consumption and behavioral responses of prey animals exposed to different levels of threat via video analysis of prey responses. An ideal predator-prey system to examine this relationship exists in northern Michigan which involves predatory Largemouth and Smallmouth Bass, and the crayfish prey that they feed upon. Crayfish have well stereotyped predator avoidance behaviors and are known to feed on aquatic plants as adults.
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