捕食风险对东方田鼠功能反应格局的作用

Effects of predation risk on the patterns of functional responses in reed vole foraging

植食性哺乳动物对食物斑块的选择和利用不仅取决于食物的可利用性,且与觅食环境潜存的各种风险紧密关联。捕食风险是否通过作用于动物觅食活动中的警觉影响其功能反应格局。在新鲜白三叶叶片构成的各类食物密集斑块上,测定东方田鼠觅食行为,建立功能反应模型,检验捕食风险对其功能反应格局的作用。结果发现,捕食风险能显著地延长东方田鼠的觅食决定时间,但其摄入率保持稳定,功能反应构型亦未发生改变,仍为Ⅱ型功能反应;除了对照组个体的采食时间随叶片大小增大无明显变动规律外,处理组个体的采食时间及对照组和处理组个体的处理时间、觅食中断时间均随叶片大小及口量的增大呈线性增高趋势,处理组个体的觅食中断时间明显大于对照组个体的;对照组和处理组个体的采食率均随叶片大小及口量呈非线性渐近递减趋势,但处理组个体的采食率较对照组个体的略有降低。结果揭示,在捕食风险压力下,虽然上述觅食参数变异能潜在地降低摄入率,但个体能通过改变觅食活动中各种警觉行为动作如降低嗅闻和静听监视动作的发生频次,增大视觉监视动作比重,以此缓冲捕食风险压力,维持摄入率。摄入率测定值与模型预测值的线性回归极显著,表明,功能反应模型具有良好的预测性。在可利用植物密集斑块,动物觅食活动中的警觉能缓冲捕食风险压力;动物摄入率是由植物大小调控的口量决定的,且受采食与处理食物竞争及觅食中断的制约;其功能反应仍属Ⅱ型功能反应。

Selection and consumption of food patches in mammalian herbivores depend not only on the availability of patches,but also on the latent risks around.Whether predation risk affect the patterns of functional responses of herbivores by influencing their vigilance in foraging is still unknown.To evaluate the effects of predation risks on patterns of functional responses of voles(Microtus fortis),we measured behavioral parameters of the voles′ foraging in food concentrated patches consisting of fresh leaves of clover(Tritolium repens),and tested a newly constructed mechanistic model of functional responses. Modeling of foraging processes indicated that predation risk significantly prolonged foraging decision time of voles.The intake rate in different patches was similar,the patterns of functional responses remained unchanged,and were still typeⅡfunctional responses.Except for cropping time in controls remaining stable with the increasing leaf size of clover,cropping time in treatments,processing time and interrupting time in both controls and treatments increased linearly with increasing bite size.The interruption time of the treatments was obviously longer than that of the controls;bite rates in both controls and treatments decreased nonlinearly,but the bite rates in treatments were slightly lowered when compared with those in controls. These results demonstrate that,although the variation of these behavioral parameters of voles under the pressure of predation risk are likely to depress intake rates,voles are able to modify the frequency of vigilance actions such as lessening the smelling and listening action and mounting the staring action,so as to effectively buffer the pressure of predation risk,thus can maintain their intake rates.A significantly linear regressive relationship was detected between the intake rate observed and that predicted by the model,indicating the predictability of the model is satisfactory.Validation of the models provided a strong support to the following hypotheses: vigilance in herbivores′ foraging is capable to buffer the pressure of prediction risks;the intake rate of herbivores is controlled by plant sizes through regulating their bite sizes,and is also constrained by competition between cropping and chewing and foraging interruption at vigilance;the responses of intake rates to plant sizes and bite sizes are still a type Ⅱ functional response as voles foraging in food-concentrated patches.