Department of Biology, University of Missouri-St. Louis, R223 Research Building, One University Boulevard, St. Louis, Missouri 63121-4400, USA.
Ecology. 2011 Mar;92(3):699-708. doi: 10.1890/10-0125.1.
Ecological communities are structured by both deterministic, niche-based processes and stochastic processes such as dispersal. A pressing issue in ecology is to determine when and for which organisms each of these types of processes is important in community assembly. The roles of deterministic and stochastic processes have been studied for a variety of communities, but very few researchers have addressed their contribution to insect herbivore community structure. Insect herbivore niches are often described as largely shaped by the antagonistic pressures of predation and host plant defenses. However host plants are frequently discrete patches of habitat, and their spatial arrangement can affect herbivore dispersal patterns. We studied the roles of predation, host plant quality, and host spatial proximity for the assembly of a diverse insect herbivore community on Quercus alba (white oak) across two growing seasons. We examined abundances of feeding guilds to determine if ecologically similar species responded similarly to variation in niches. Most guilds responded similarly to leaf quality, preferring high-nitrogen, low-tannin host plants, particularly late in the growing season, while bird predation had little impact on herbivore abundance. The communities on the high-quality plants tended to be larger and, in some cases, have greater species richness. We analyzed community composition by correlating indices of community similarity with predator presence, leaf quality similarity, and host plant proximity. Birds did not affect community composition. Community similarity was significantly associated with distance between host plants and uncorrelated with leaf quality similarity. Thus although leaf quality significantly affected the total abundance of herbivores on a host plant, in some cases leading to increased species richness, dispersal limitation may weaken this relationship. The species composition of these communities may be driven by stochastic processes rather than variation in host plant characteristics or differential predation by insectivorous birds.
生态群落的结构既受到基于生态位的确定性过程的影响，也受到扩散等随机过程的影响。在生态学中，一个紧迫的问题是确定在何时以及对于哪些生物，这些类型的过程在群落组装中更为重要。已经有许多研究人员研究了确定性和随机性过程的作用，但很少有人研究它们对昆虫食草动物群落结构的贡献。昆虫食草动物的生态位通常被描述为主要受到捕食和寄主植物防御的拮抗压力的影响。然而，寄主植物通常是离散的栖息地斑块，它们的空间排列会影响食草动物的扩散模式。我们在两个生长季节里，研究了捕食作用、寄主植物质量和寄主植物空间接近度对不同的昆虫食草动物群落在白栎上组装的作用。我们检查了取食群体的丰度，以确定生态相似的物种是否对生态位的变化有相似的反应。大多数群体对叶质量的反应相似，喜欢高氮、低单宁的寄主植物，尤其是在生长季节后期，而鸟类捕食对食草动物的丰度几乎没有影响。高质量植物上的群落往往更大，在某些情况下，物种丰富度更高。我们通过将群落相似性指数与捕食者存在、叶片质量相似性和寄主植物接近度相关联来分析群落组成。鸟类没有影响群落组成。群落相似性与寄主植物之间的距离显著相关，与叶片质量相似性无关。因此，尽管叶片质量显著影响了寄主植物上食草动物的总丰度，在某些情况下导致物种丰富度增加，但扩散限制可能会削弱这种关系。这些群落的物种组成可能是由随机过程驱动的，而不是寄主植物特征的变化或食虫鸟类的差异捕食。
