Background/Question/Methods How much do limiting similarity and environmental filtering influence community assembly processes? This key question in community ecology has recently been revisited using functional traits, demonstrating that both limiting similarity and habitat filtering can act to structure plant communities, but debate remains on the relative strength of these processes. Substantial hurdles in this research are 1. the use of limited trait data which overlooks the contributions of rare species and intraspecific variation, and 2. examining particular drivers of community assembly relevant to real-world ecosystems. This study asks the question: "what is the relative importance of limiting similarity and environmental filtering in structuring plant communities in grassland plant communities under herbivory in Inner Mongolia, China?" In this study functional trait measurements were carried out a the level of the individual plant. The grasslands of Inner Mongolia present a good test case for examining how functional traits reflect the processes of habitat filtering or limiting similarity in structuring communities, with simple community structure and the clearly important influences of herbivory by sheep and grasshoppers on plant communities. This research context also relates to the broader questions of biodiversity and sustainable rangeland management in the Inner Asian steppe.

Results/Conclusions The traits measured at the level of the individual plant were leaf mass per unit area (LMA), height, maximum photosynthetic rate, water use efficiency, C, N, and P concentrations, and length of longest leaf, and aboveground biomass. Substantial intraspecific variation was found across the 18 species measured in 2008 and 2009, both across and within growing seasons. Plant communities under a gradient of sheep grazing intensity exhibited reduced species richness, while experimental manipulations of grasshopper herbivory did not impact species richness. Measures of functional trait variation overlap demonstrated the relative influence of limiting similarity (communities with less trait similarity than expected by chance) versus environmental filtering (communities with greater trait similarity than expected by chance) under these contrasting herbivory regimes. This study demonstrates the value of functional trait measurements at the level of the individual and examining drivers of community assembly relevant to sustainable rangeland management.