Competition, predation, and migration: individual choice patterns of Serengeti migrants captured by hierarchical models
Competition, predation, and migration: individual choice patterns of Serengeti migrants captured by hierarchical models
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DOI：
10.1890/13-1446.1
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发表时间：
2014-08-01
影响因子：
6.1
通讯作者：
Haydon, Daniel T.
中科院分区：
文献类型：
--
作者：
Hopcraft, J. Grant C.;Morales, J. M.;Haydon, Daniel T.
大型食草动物的迁徙发生在食物质量或食物丰度的梯度上，这些梯度通常由降雨量、海拔或纬度的基本地理模式决定，进而导致种间竞争程度和接触捕食者的程度发生变化。然而，捕食的自上而下效应与竞争资源的自下而上效应在形成迁徙中的作用还没有得到很好的理解。我们研究了30只在塞伦盖蒂-马拉生态系统中季节性迁徙的GPS无线电领角马和斑马，以了解捕食和食物供应如何不同地影响这些共同迁徙物种的个体运动模式。对与草生物量、优质食物斑块和捕食风险相关的运动轨迹(方向和距离)的层次分析表明，角马倾向于根据食物质量进行移动，而很少关注捕食风险。相比之下，个体斑马的运动反映了捕食风险和获得足够生物量的高质量食物之间的平衡。我们的分析显示了两个迁徙物种如何对同一景观的不同属性做出反应。与大多数其他动物运动研究相反的是，我们发现，当当地资源丰富时，这两个物种每天都会比资源稀缺时移动得更远。在雨季，当放牧质量达到顶峰时，角马和斑马都会移动最远的距离，不会在局部地区定居以延长放牧时间。我们认为，高质量斑块的这种间断移动可以用密度依赖来解释，即大量相互竞争的个体(多达165万只食草动物)迅速耗尽了当地的放牧机会。这些发现捕捉到了捕食和竞争在塑造动物迁徙中的作用，这些迁徙经常被声称，但很少被测量。
Large-herbivore migrations occur across gradients of food quality or food abundance that are generally determined by underlying geographic patterns in rainfall, elevation, or latitude, in turn causing variation in the degree of interspecific competition and the exposure to predators. However, the role of top-down effects of predation as opposed to the bottom-up effects of competition for resources in shaping migrations is not well understood. We studied 30 GPS radio-collared wildebeest and zebra migrating seasonally in the Serengeti-Mara ecosystem to ask how predation and food availability differentially affect the individual movement patterns of these co-migrating species. A hierarchical analysis of movement trajectories (directions and distances) in relation to grass biomass, high-quality food patches, and predation risk show that wildebeest tend to move in response to food quality, with little attention to predation risk. In contrast, individual zebra movements reflect a balance between the risk of predation and the access to high-quality food of sufficient biomass. Our analysis shows how two migratory species move in response to different attributes of the same landscape. Counterintuitively and in contrast to Most other animal movement studies, we find that both species move farther each day when resources are locally abundant than when they are scarce. During the wet season when the quality of grazing is at its peak, both wildebeest and zebra move the greatest distances and do not settle in localized areas to graze for extended periods. We propose that this punctuated movement in high-quality patches is explained by density dependency, whereby large groups of competing individuals (up to 1.65 million grazers) rapidly deplete the localized grazing opportunities. These findings capture the roles of predation and competition in shaping animal migrations, which are often claimed but rarely measured.