Biological diversity refers to life at all levels of organization, from genes within populations to the global arrays of species (Wilson 1992). It is often assumed, though, that any discussion of biodiversity is focused at the species level. However, this discussion is still highly complex given that we know only a small percentage of the total microbial, plant, and animal species. Though estimates of microbial, plant, and animal species are as imprecise as between 5 and 50 million (Tilman 1999), there are many arguments for conserving biodiversity. For rangeland management, the concept of biological diversity is typically focused on plant species richness, evenness, and heterogeneity at community-level spatial scales (West 1993). Species diversity is clearly a major determinant of many ecological processes, especially those related to resilience and resistance (Tilman 1998). Given that over 75% of the earth's ecosystems are manipulated for human purposes (Moguel & Toledo 1999), maintaining abilities of these systems to buffer (resistence) and recover from disturbances (resilience) is key to conserving inherent ecological functions (Peterson et al. 1998). For example, one consequence of species loss is a limit to the potential ways an ecosystem can reorganize following disturbance, an important component of ecosystem resilience (Peterson et al. 1998). It is well recognized that we are currently in the midst of the sixth major period of extinction on earth and that this current extinction period is biologically driven (Chapin et al. 1998). The potential for significant impacts on ecosystem functions due to losses of biodiversity is large and immediate.