Effects of Kangaroo Rats on Plant Species Dominance in a Chihuahuan Desert Grassland at the Sevilleta National Wildlife Refuge, New Mexico (1988)

Our objective was to evaluate the effects of burrowing activities by banner-tail kangaroo rats (Dipodomys spectabilis Merriam) on plant community structure and species dominance for two patch types at an ecotone between shortgrass steppe and desert grasslands in New Mexico, USA. Ten mounds produced by kangaroo rats were selected in patches dominated by Bouteloua gracilis (the dominant in shortgrass steppe communities) and ten mounds were selected in patches dominated by Bouteloua eriopoda (the dominant in Chihuahuan desert grasslands). Plant cover and density by species were sampled from three locations associated with each mound: the mound proper, the edge of the mound in the transition area, and the off-mound vegetation. Similar cover of B. eriopoda for the edges of mounds in both patch types indicates the ability of this species to respond to animal disturbances regardless of the amount of cover in the surrounding undisturbed vegetation. By contrast, cover of B. gracilis was low for all mounds and mound edges in patches dominated by this species. Much higher cover of B. eriopoda on mound edges compared to the undisturbed vegetation in B. gracilis- dominated patches indicates that kangaroo rats have important positive effects on this species. Lower cover of perennial grasses and higher cover of forbs, shrubs, and succulents on the edges of mounds in B. eriopoda - dominated patches compared to patches dominated by B. gracilis indicate the importance of surrounding vegetation to plant responses on disturbed areas. Our results show that kangaroo rats have important effects on both species dominance and composition for different patch types, and may provide a mechanism for small-scale dominance patterns at an ecotonal boundary; thus providing further support for their role as keystone species in desert grasslands.