Diversity of a grassland rodent community at varying temporal scales: The role of ecologically dominant species

Using a long-term data set (1989-1999), we examined how changes in abundanc e of 2 ecologically dominant species, prairie voles (Microtus ochrogaster) and hispid cotton rats (Sigmodon hispidus), affected the local diversity of a grassland rodent community at varying temporal scales. Species richness was associated positively with long-term fluctuations in the abundance of p rairie voles and cotton rats over the 10-year period. Although increased vo le densities consistently had a significantly negative effect on total comm unity evenness, evenness of other community members was unaffected by fluct uating vole densities. Presence of cotton rats negatively affected both the relative abundance of other community members and the species richness dur ing the years of high density (1991-1995), but did not exhibit longer-term influences. Thus, despite their numerical dominance, changes in prairie vol e abundance had little ecological effect on the rest of the community, wher eas the influence of cotton rats was density- and temporally dependent.