Species richness — primary productivity relationship of plants and small mammals in the Inner Mongolian steppes, China

We studied the relationship between primary productivity and plant and small mammal species richness in Inner Mongolian steppes, using data collected from 1980–1987. The productivity-plant species richness pattern was unimodal at our study site and consistent over time. Quadratic terms of regressions of plant species richness on plant aboveground biomass for the 7-year data were either significant (p<0•05) or marginally significant (p=0•05 or 0•06). However, the productivity-small mammal species richness pattern was not unimodal (p>0•1). The relationship between small mammal species richness and plant aboveground biomass was linear and negative for 7 years (p<0•05, or p<0•06). Plants are sedentary, and more likely to compete for limiting resources with neighboring plants, whereas some small mammals use different habitats at different times during a year because of migration or dispersal. The productivity-plant species richness pattern could be unimodal because of the competition dominance of a few plant species along a resource gradient or because of assemblage-level thinning. Primary productivity may not be a good predictor of small mammal species richness at small spatial scales due to movement and spatial use pattern. Productivity is a measure of plant community production, but not resources available for plants. More experimental studies are needed to elucidate the mechanism of the unimodal productivity-plant species richness pattern.