Département de biologie and Centre d'étude de la Forêt; Université Laval, Québec, Québec, Canada.
PLoS One. 2013 Sep 11;8(9):e73324. doi: 10.1371/journal.pone.0073324. eCollection 2013.
Spatial heterogeneity in the strength of trophic interactions is a fundamental property of food web spatial dynamics. The feeding effort of herbivores should reflect adaptive decisions that only become rewarding when foraging gains exceed 1) the metabolic costs, 2) the missed opportunity costs of not foraging elsewhere, and 3) the foraging costs of anti-predator behaviour. Two aspects of these costs remain largely unexplored: the link between the strength of plant-herbivore interactions and the spatial scale of food-quality assessment, and the predator-prey spatial game. We modeled the foraging effort of free-ranging plains bison (Bison bison bison) in winter, within a mosaic of discrete meadows. Spatial patterns of bison herbivory were largely driven by a search for high net energy gains and, to a lesser degree, by the spatial game with grey wolves (Canis lupus). Bison decreased local feeding effort with increasing metabolic and missed opportunity costs. Bison herbivory was most consistent with a broad-scale assessment of food patch quality, i.e., bison grazed more intensively in patches with a low missed opportunity cost relative to other patches available in the landscape. Bison and wolves had a higher probability of using the same meadows than expected randomly. This co-occurrence indicates wolves are ahead in the spatial game they play with bison. Wolves influenced bison foraging at fine scale, as bison tended to consume less biomass at each feeding station when in meadows where the risk of a wolf's arrival was relatively high. Also, bison left more high-quality vegetation in large than small meadows. This behavior does not maximize their energy intake rate, but is consistent with bison playing a shell game with wolves. Our assessment of bison foraging in a natural setting clarifies the complex nature of plant-herbivore interactions under predation risk, and reveals how spatial patterns in herbivory emerge from multi-scale landscape heterogeneity.
营养相互作用强度的空间异质性是食物网空间动态的一个基本特征。食草动物的觅食努力应该反映出适应性决策，只有当觅食收益超过 1）代谢成本、2）不在其他地方觅食的错过机会成本和 3）反捕食行为的觅食成本时，这些决策才会有回报。这些成本的两个方面在很大程度上仍未得到探索：植物-食草动物相互作用的强度与食物质量评估的空间尺度之间的联系，以及捕食者-猎物的空间博弈。我们在离散草地镶嵌体中，对自由放养的平原野牛（Bison bison bison）的觅食努力进行了建模。野牛的觅食模式在很大程度上是由寻找高净能量收益驱动的，其次是与灰狼（Canis lupus）的空间博弈。随着代谢和错过机会成本的增加，野牛减少了局部的觅食努力。野牛的食草行为最符合对食物斑块质量的广泛评估，即野牛在错过机会成本相对较低的斑块中比在景观中其他可用斑块中更密集地放牧。野牛和狼在同一草地上的出现概率高于随机预期。这种共存表明，狼在与野牛进行的空间博弈中处于领先地位。狼在微观尺度上影响了野牛的觅食行为，因为当野牛在狼到达风险相对较高的草地上时，每到一个觅食站，它们的进食量就会减少。此外，野牛在较大的草地上留下的高质量植被比在较小的草地上多。这种行为并不能使它们的能量摄入率最大化，但与野牛与狼玩的壳游戏一致。我们对野牛在自然环境中的觅食行为的评估阐明了在捕食风险下植物-食草动物相互作用的复杂性质，并揭示了食草行为如何从多尺度景观异质性中出现。
