Stewart Kelley M, Bowyer R Terry, Kie John G, Dick Brian L, Ruess Roger W
Natural Resources and Environmental Science, University of Nevada Reno, 1000 Valley Road, Reno, NV 89512, USA.
Oecologia. 2009 Aug;161(2):303-12. doi: 10.1007/s00442-009-1376-z. Epub 2009 May 30.
Large, herbivorous mammals have profound effects on ecosystem structure and function and often act as keystone species in ecosystems they inhabit. Density-dependent processes associated with population structure of large mammals may interact with ecosystem functioning to increase or decrease biodiversity, depending on the relationship of herbivore populations relative to the carrying capacity (K) of the ecosystem. We tested for indirect effects of population density of large herbivores on plant species richness and diversity in a montane ecosystem, where increased net aboveground primary productivity (NAPP) in response to low levels of herbivory has been reported. We documented a positive, linear relationship between plant-species diversity and richness with NAPP. Structural equation modeling revealed significant indirect relationships between population density of herbivores, NAPP, and species diversity. We observed an indirect effect of density-dependent processes in large, herbivorous mammals and species diversity of plants through changes in NAPP in this montane ecosystem. Changes in species diversity of plants in response to herbivory may be more indirect in ecosystems with long histories of herbivory. Those subtle or indirect effects of herbivory may have strong effects on ecosystem functioning, but may be overlooked in plant communities that are relatively resilient to herbivory.
大型食草哺乳动物对生态系统的结构和功能具有深远影响，并且在它们栖息的生态系统中常常充当关键物种。与大型哺乳动物种群结构相关的密度依赖过程可能与生态系统功能相互作用，从而增加或减少生物多样性，这取决于食草动物种群与生态系统承载能力（K）的关系。我们在一个山地生态系统中测试了大型食草动物种群密度对植物物种丰富度和多样性的间接影响，据报道，该生态系统中低水平的食草作用会导致地上净初级生产力（NAPP）增加。我们记录了植物物种多样性和丰富度与NAPP之间呈正线性关系。结构方程模型揭示了食草动物种群密度、NAPP和物种多样性之间存在显著的间接关系。在这个山地生态系统中，我们观察到大型食草哺乳动物的密度依赖过程通过NAPP的变化对植物物种多样性产生间接影响。在具有长期食草历史的生态系统中，植物物种多样性对食草作用的响应可能更为间接。食草作用的这些微妙或间接影响可能对生态系统功能产生强烈影响，但在对食草作用具有相对恢复力的植物群落中可能会被忽视。
