植食性哺乳动物能量收益增长减速机制的检验

Validation of the mechanism for decelerating energy gains in mammalian herbivores

能量收益函数描述了植食性哺乳动物在植物斑块的食物摄入量与在斑块停留时间的函数关系,为觅食生态学理论的重要组成部分。在新鲜白三叶叶片构成的各类叶片斑块上,测定东方田鼠的觅食行为,建立其能量收益函数模型,分析植食性哺乳动物能量收益增长减速的机制。研究结果表明,东方田鼠觅食大叶片时,叶片干物质收益与停留时间呈非线性渐进函数关系,能量收益函数为渐进函数;觅食中、小型叶片时,叶片干物质收益与停留时间呈线性函数关系,能量收益函数为线性函数;没有检测到东方田鼠的能量收益动态呈分段线性函数或S型函数增长。东方田鼠在大、中型叶片斑块觅食时,随停留时间的增大,口量呈线性或指数递减,而处理时间则呈线性或指数递增,采食时间、间隔时间及咀嚼频次保持相对稳定,瞬时摄入率呈减小趋势;东方田鼠在小叶片斑块觅食时,觅食行为参数口量、摄入率、采食时间、间隔时间、处理时间及咀嚼频次均保持相对稳定。研究结果充分验证了,植食性哺乳动物在消费植被过程中,大型可利用性植物减少,受植物大小调控的动物口量减小,处理时间增加,引起瞬时摄入率降低,导致其能量收益增长减速的假说。

The gain function,which describes the amount of food consumed by mammalian herbivores in a plant patch as a function of their residence time in the patch,is the central part of the foraging theory.In this study,the foraging behavior of voles （Microtus fortis） was observed in the patches of fresh clover （Trifolium repens） leaves,the models for their energy gain functions were developed,and the mechanism for decelerating energy gains in mammalian herbivores was validated.The results showed an asymptotic gain function for the voles foraging in the large leaf patches,whereas a linear gain function for the voles foraging in the small and medium leaf patches.No piecewise linear or sigmoid gain functions were detected in the voles foraging in the patches.Behavioral parameters regulating instantaneous intake rates changed dynamically with the vole＇s residence time in the patches：in the medium and large leaf patches,bite sizes linearly or exponentially decreased,but processing time linearly or exponentially increased with increasing residence time,although the cropping time,interval time and chewing frequency remained constant.Instantaneous intake rates also declined with increasing residence time of the voles in the patches.In small leaf patches,the behavioral parameters including bite sizes,instantaneous intake rates,cropping time,interval time,processing time and chewing frequency remained constant regardless of the voles＇ residence time in the patches.Validation of these models provided a strong support to the hypothesis that deceleration in the energy gain in mammalian herbivores resulted from a decrease in instantaneous intake rates due to reduced availability of large plants,decreased bite sizes and increased processing time as the patches were depleted.