Lancaster Jill, Downes Barbara J
Department of Resource Management and Geography, University of Melbourne, 221 Bouverie Street, Parkville, VIC, 3010, Australia,
Oecologia. 2014 Dec;176(4):985-96. doi: 10.1007/s00442-014-3062-z. Epub 2014 Sep 5.
Many communities comprise species that select resources that are patchily distributed in an environment that is otherwise unsuitable or suboptimal. Effects of this patchiness can depend on the characteristics of patch arrays and animal movements, and produce non-intuitive outcomes in which population densities are unrelated to resource abundance. Resource mosaics are predicted to have only weak effects, however, where patches are ephemeral or organisms are transported advectively. The running waters of streams and benthic invertebrates epitomize such systems, but empirical tests of resource mosaics are scarce. We sampled 15 common macroinvertebrates inhabiting distinct detritus patches at four sites within a sand-bed stream, where detritus formed a major resource of food and living space. At each site, environmental variables were measured for 100 leaf packs; invertebrates were counted in 50 leaf packs. Sites differed in total abundance of detritus, leaf pack sizes and invertebrate densities. Multivariate analysis indicated that patch size was the dominant environmental variable, but invertebrate densities differed significantly between sites even after accounting for patch size. Leaf specialists showed positive and strong density-area relationships, except where the patch size range was small and patches were aggregated. In contrast, generalist species had weaker and variable responses to patch sizes. Population densities were not associated with total resource abundance, with the highest densities of leaf specialists in sites with the least detritus. Our results demonstrate that patchy resources can affect species even in communities where species are mobile, have advective dispersal, and patches are relatively ephemeral.
许多群落包含这样一些物种，它们会选择在原本不适合或并非最优的环境中呈斑块状分布的资源。这种斑块状分布的影响可能取决于斑块阵列的特征和动物的移动情况，并产生一些非直观的结果，即种群密度与资源丰度无关。然而，据预测，在斑块短暂存在或生物通过平流进行迁移的情况下，资源镶嵌体的影响较弱。溪流的流水和底栖无脊椎动物就是这类系统的典型代表，但对资源镶嵌体的实证研究却很匮乏。我们在一条沙床溪流中的四个地点，对栖息在不同碎屑斑块上的15种常见大型无脊椎动物进行了采样，其中碎屑构成了食物和生存空间的主要资源。在每个地点，对100个树叶包的环境变量进行了测量；在50个树叶包中对无脊椎动物进行了计数。各地点在碎屑的总丰度、树叶包大小和无脊椎动物密度方面存在差异。多变量分析表明，斑块大小是主要的环境变量，但即使在考虑了斑块大小之后，各地点的无脊椎动物密度仍存在显著差异。除了斑块大小范围较小且斑块聚集的情况外，专食树叶的物种表现出正的且强烈的密度-面积关系。相比之下，广食性物种对斑块大小的反应较弱且多变。种群密度与总资源丰度无关，在碎屑最少的地点，专食树叶的物种密度最高。我们的结果表明，即使在物种具有移动性、通过平流进行扩散且斑块相对短暂的群落中，斑块状资源也会对物种产生影响。
