Abstract
Predation involves more than just predators consuming prey. Indirect effects, such as fear responses caused by predator presence, can have consequences for prey life history. Laboratory experiments have shown that some rodents can recognize fear in conspecifics via alarm pheromones. Individuals exposed to alarm pheromones can exhibit behavioural alterations that are similar to those displayed by predator-exposed individuals. Yet the ecological and evolutionary significance of alarm pheromones in wild mammals remains unclear. We investigated how alarm pheromones affect the behaviour and fitness of wild bank voles (Myodes glareolus) in outdoor enclosures. Specifically, we compared the effects of exposure of voles living in a natural environment to a second-hand fear cue, bedding material used by predator-exposed voles. Control animals were exposed to bedding used by voles with no predator experience. We found a ca. 50% increase in litter size in the group exposed to the predator cue. Furthermore, female voles were attracted to and males were repelled by trap-associated bedding that had been used by predator-exposed voles. Movement and foraging were not significantly affected by the treatment. Our results suggest that predation risk can exert population-level effects through alarm pheromones on prey individuals that did not encounter a direct predator cue.
Highlights
Many organisms, including vertebrates, invertebrates, and plants, respond to predation threats by producing alarm signals.[16]
We tested the hypothesis that wild bank voles (Myodes glareolus), a model prey species in many studies of predator-prey interactions, would show antipredator-like responses when exposed to AP11,26, since the murine alarm pheromones (AP) shares structural similarity with predator scent[21]
Litter size was significantly greater by 1.9 ± 0.7 pups in AP enclosures compared to control enclosures (p = 0.013; Table 1, Fig. 1)
Summary
Many organisms, including vertebrates, invertebrates, and plants, respond to predation threats by producing alarm signals. (reviewed by Verheggen et al.)[16]. Neurobiological and psychological experiments show that individuals can recognise stressed conspecifics from the AP left behind following a stressful situation[19] The receivers of this indirect signal increase their vigilance and risk assessment behaviour, i.e., change their behaviour in ways that are similar to individuals that encountered a direct predator cue[18]. In an experimental indoor arena, Cabrera voles (Microtus cabrerae) avoided areas with the scent marks of conspecifics that experienced various predation risks[23]. Wild rodents are ideally suited for studying the ecology of predator cues. These animals have a highly developed olfactory system, and odours play a key role in their behavioural decision-making[25]. These behavioural and ecological responses should lead to poorer body condition, which in turn should lead to a smaller proportion of breeding females and a smaller litter sizes on average[26,28]
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