Submitted to: Journal of Vegetation Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/24/1998
Publication Date: N/A
Interpretive Summary: Bannertail kangaroo rats are important components of rangelands in the Southwestern U.S. We analyzed the effects of burrowing activities by kangaroo rats on vegetation dynamics for shortgrass steppe rangelands dominated by blue grama and for Chihuahuan desert grasslands dominated by black grama. We sampled vegetation on ten mounds in patches dominated by blue grama and ten mounds in patches dominated by black grama located at the Sevilleta National Wildlife Refuge in central New Mexico. We found that black grama cover was positively influenced by the presence of kangaroo rat mounds, and blue grama was negatively affected by mounds. These different responses by the two grama species reflects differences in their life history traits and their ability to respond to soil disturbances. Lower cover of other perennial grasses and higher cover of forbs and shrubs on mounds in black grama patches compared to mounds in blue grama patches indicate the importance of the surrounding vegetation to plant responses o disturbed areas. Our results are important because they provide further evidence for the role of kangaroo rats as keystone species in arid rangelands since their burrowing activities determine, at least in part, patterns in plant species dominance.
Technical Abstract: 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 ecotonal boundary between shortgrass steppe and desert grasslands in New Mexico, USA. Ten mounds produced by kangaroo rats were selected in patches sdominated 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 gundisturbed 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.