Effects Ofprcdation Risk And Emotion On Foraging Behavior In Reed Voles

Selection and consumption of food patches in mammalian herbivores depend notonly on the availability of patches, but also on the latent risks around, and alsoinfluenced by emotional state following exposure to environmental changes. Whetherpredation risk affect the patterns of functional responses of herbivores by influencingtheir vigilance in foraging is still unknown. We also wonder if emotional state affect theintake rate of herbivores in foraging gramineous plant that equipped with combdefensing.To evaluate the effects of predation risk on patterns of functional responses ofvoles (Microtus fortis) foraging, as well as the effects of target emotional states such asrelaxed calm and excited happy that induced by different periods of starvation onforaging behavior, we measured behavioral parameters of the voles’ foraging in foodconcentrated patches consisted of fresh leaves of clover (Tritolium repens) andDigitaria sagunialis, and tested our novelly constructed mechanistic model offunctional responses and cognitive bias approach.Our results showed that,①predation risk significantly prolonged foraging decisiontime of voles. The intake rate in different patches was similar, and the patterns offunctional responses were still typeⅡfunctional responses. Except for cropping time ofthe controls remaining stable with the increasing leaf size of clover, cropping time intreatments, processing time and interrupting time in both controls and treatments allincreased linearly with increasing bite size. The interruption time of the treatments waslonger than that of the controls; Bite rates in both controls and treatments all decreasednonlinearly, but the bite rates in treatments were lowered slightly when compared withthose in controls. These results revealed that, although the variation of these behavioralparameters of voles under the pressure of predation risk are likely to depress intakerates, voles are able to modify the frequency of vigilance actions such as lessening thesmelling and listening actions and mounting the staring action, so as to effectivelybuffer the pressure of predation risks, thus can maintain their intake rates.A significantlylinear regressive relationship was detected between the observed intake rate and thatpredicted by the model, which indicated that the predictability of the model issatisfactory. The validation of the models provided a strong support to the followinghypotheses: herbivores are capable to buffer the pressure of prediction risks viavigilance; the intake rate of herbivores is controlled by plant sizes through regulatingtheir bite sizes, and is also constrained by competition between cropping and chewingand foraging interruption cause by vigilance; the responses of intake rates to plant sizesand bite sizes are still a type Ⅱ functional response as voles foraging infood-concentrated patches.②Being in a relaxed calm emotional state, foraging decision time of females was longer than that of males. Females preferred to bite at the base of leaves markedly,while males preferred base and middle part. Voles’ intake rate when biting at the base ofleaves was significantly and extremely significantly higher than biting at the middle partand tip, and intake rate when biting at the middle part was extremely significantlyhigher than biting at the tip. Voles’ cropping time when biting at tip was extremelysignificantly higher than biting at the base and middle part, and cropping time whenbiting at the middle part was significantly higher than that when bite at base. Theseresults listed above indicated that individuals that being relaxed calm emotional state areable to accurately distinguish and determine the biting location that can maximize theirintake rate, thus the novel cognitive bias approach for reed voles is effective in valuetheir cognitive ability.③Foraging decision time of treatments being in exited happy emotional state wassignificantly shorter than that of controls being in relaxed calm emotional state. Thepatterns of biting locations of females and males in controls were the same, and showeda obviously preferance to middle part. The intake rate of treatments when biting at thebase was significantly and extremely significantly higher than biting at the middle partand tip, and the intake rate when biting at the middle part was extremely significantlyhigher than biting at the tip.