Increasingly functional diversity patterns are being used to infer the processes regulating community assembly in plant communities. Much of this research has focused on how these processes change along environmental gradients. Environmental filtering is often postulated to play a predominate role in low resource areas and competition is often thought dominant in high resource areas. This research, however, has overlooked a key assembly process in many communities-the effects of generalist small mammal consumers. We investigated the effects of herbivorous voles on the trait composition of eight grassland sites located along a resource gradient. We hypothesize that herbivory will interact with plant competition to influence community trait composition. Specifically, we predict that vole foraging may shift specific leaf area (SLA), as it is correlated with higher foliar N and more susceptible to herbivory, and predict these shifts will influence competition in high resources areas. We established 9 m x 9 m paired plots of a small mammal exclosure and a control at each site. Within six subplots per plot we measured species composition and plant functional traits SLA, height and leaf water content. We then calculated estimates of multivariate functional diversity, single trait community weighted means (CWM) and functional diversity
Results/Conclusions
Small mammals shifted different components of functional diversity along the environmental gradient although they did not alter species richness. Multivariate functional diversity decreased as resources increased but more strongly in the absence of small mammals, suggesting that small mammals mediated competitive interactions as resources increased. Plant height increased with increasing resources irrespective of small mammals, but the increase in SLA along the same gradient was dampened by small mammals. Conversely, functional dispersion in height increased with resources but less strongly in the presence of small mammals while small mammals had no affect on the decrease in SLA functional dispersion with increasing resources. These data suggest that small mammals do influence assembly processes along environmental gradients by preferentially foraging on high SLA species in high resource environments and mediating the role that competitive interactions play in structuring communities at high resources.