The Effect of Kangaroo-Rat Activity on Plant Species Composition at the Sevilleta National Wildlife Refuge, New Mexico (1999)

Our objective was to evaluate the effects of kangaroo rat mounds on species diversity and composition at a semiarid-arid grassland ecotone. We expected that source populations of plants occurring on kangaroo rat mounds have important influences on the species composition of vegetation at the landscape scale, and that these influences differ by grassland type. Our study was conducted at the Sevilleta LTER in New Mexico, where a grassland type dominated by Bouteloua gracilis, a shortgrass steppe species, and a grassland type dominated by B. eriopoda, a desert grassland species, meet to form patches across the landscape.Four 0.4 ha plots were sampled for species diversity and composition in a regular 7m x 7m grid in each grassland type. Kangaroo rat mounds were also mapped and sampled for vegetation measures in four areas of 1.6 ha in each type. The landscape scale abundance of many subordinate species was increased significantly by populations occurring on kangaroo rat mounds in both grassland types. However, the area affected by the burrowing activity of kangaroo rats was twice as large in the B. eriopoda dominated grassland type. Furthermore, dominant plants on mounds in the B. eriopoda type were also abundant in off-mound areas whereas dominant plants on mounds in the B. gracilis type were not as abundant off-mound. These results indicate that the presence of mounds in the B. gracilis dominated type is creating islands of plant communities that are distinct from the rest of the grassland. Therefore, the occurrence of certain plant species in this grassland type may be intimately associated with the disturbance regime at this ecotone. This study demonstrates that effects of small burrowing animals may facilitate the coexistence of species at this ecotone.

本研究旨在评估更格卢鼠（kangaroo rat）丘堆对半干旱-干旱草原生态交错带的物种多样性与群落组成的影响。我们推测，栖息于更格卢鼠丘堆上的植物源种群会对景观尺度下的植被物种组成产生重要调控作用，且该作用因草原类型不同而存在差异。本研究于新墨西哥州的塞维莱塔长期生态研究站点（Sevilleta LTER）开展，该区域内两种草原类型交错分布形成景观斑块：一种为以短草草原优势种细茎格兰马草（Bouteloua gracilis）为主的草原，另一种为以荒漠草原优势种毛颖格兰马草（Bouteloua eriopoda）为主的草原。针对每种草原类型，我们采用7m×7m的规则网格布设样地，共设置4块面积为0.4公顷的样方以调查物种多样性与群落组成；同时在每种类型的4块1.6公顷的区域内对更格卢鼠丘堆进行测绘，并开展植被特征采样。在两种草原类型中，栖息于更格卢鼠丘堆上的植物源种群均显著提升了景观尺度下多数从属物种的多度。但以毛颖格兰马草为主的草原中，受更格卢鼠掘洞活动影响的区域面积是另一类草原的两倍。此外，毛颖格兰马草型草原丘堆上的优势植物在丘堆外区域同样具有较高多度，而细茎格兰马草型草原丘堆上的优势植物在丘堆外区域的多度则相对较低。上述结果表明，细茎格兰马草型草原中的更格卢鼠丘堆形成了与周边草原群落显著不同的岛屿状植物群落。因此，该草原类型中部分植物物种的出现可能与该生态交错带的干扰体系密切相关。本研究证实，小型掘洞动物的活动可促进该生态交错带内物种的共存。