Negative effects of an exotic grass invasion on small-mammal communities

Exotic invasive species can directly and indirectly influence natural ecological communities. Cheatgrass (Bromus tectorum) is non-native to the western United States and has invaded large areas of the Great Basin. Changes to the structure and composition of plant communities invaded by cheatgrass likely have effects at higher trophic levels. As a keystone guild in North American deserts, granivorous small mammals drive and maintain plant diversity. Our objective was to assess potential effects of invasion by cheatgrass on small-mammal communities. We sampled small-mammal and plant communities at 70 sites (Great Basin, Utah). We assessed abundance and diversity of the small-mammal community, diversity of the plant community, and the percentage of cheatgrass cover and shrub species. Abundance and diversity of the small-mammal community decreased with increasing abundance of cheatgrass. Similarly, cover of cheatgrass remained a significant predictor of small-mammal abundance even after accounting for the loss of the shrub layer and plant diversity, suggesting that there are direct and indirect effects of cheatgrass. The change in the small-mammal communities associated with invasion of cheatgrass likely has effects through higher and lower trophic levels and has the potential to cause major changes in ecosystem structure and function.

外来入侵物种可直接或间接影响自然生态群落。旱雀麦（Bromus tectorum）并非美国西部本土物种，已入侵大盆地（Great Basin）的大片区域。受旱雀麦入侵的植物群落结构与组成发生变化，可能对更高营养级产生影响。作为北美沙漠中的关键功能类群（keystone guild），食种子小型哺乳动物驱动并维持着植物多样性。本研究旨在评估旱雀麦入侵对小型哺乳动物群落的潜在影响。我们在犹他州大盆地的70个样地开展了小型哺乳动物与植物群落采样，并分别评估了小型哺乳动物群落的丰度与多样性、植物群落多样性，以及旱雀麦盖度与灌木物种占比。研究结果显示，小型哺乳动物群落的丰度与多样性随旱雀麦丰度的升高而降低。类似地，即便在控制了灌木层丧失与植物多样性下降的影响后，旱雀麦盖度仍是小型哺乳动物丰度的显著预测因子，这表明旱雀麦对小型哺乳动物群落存在直接与间接的双重影响效应。与旱雀麦入侵相关的小型哺乳动物群落变化，可能通过更高与更低营养级产生级联效应，并有可能引发生态系统结构与功能的重大改变。