On the role of small mammals in mediating climatically driven vegetation change

Biotic and abiotic processes jointly influence natural systems, yet opportu nities to integrate studies of both processes are uncommon. For two decades we have excluded different subsets of the small mammal community from a se ries of plots near a grassland-desert ecotone in the northern Chihuahuan De sert. These studies spanned a period of historically high winter rainfall, allowing us to distinguish the effects of climate and small mammals on the composition and patch structure of vegetation. Removal of only kangaroo rat s (Dipodomys) or of all small mammals led to increased cover of large herba ceous vegetation. The size of vegetative patches increased in all plots but this increase was three times greater where all rodents were removed. Thus , the activity of small mammals that forage under and near shrub canopies a ppear to significantly inhibit the expansion of existing vegetative patches , and may have a stronger influence on habitat structure than previously re cognized.