The broad aim of this project is to search for generalities in assembly rules for herbaceous plant communities i.e. predictive rules governing community structure. The concept of limiting similarity is a niche-based ‘rule’ suggesting that there is a limit to how similar coexisting species can be, if they are both to persist. Some support has been found for limiting similarity in plant communities. The common approach to this type of study is to look for non-random patterns of species/trait-based associations in small-scale plots. Recent advances in functional ecology, and data availability on species traits and phylogenetic relationships, has great potential for advancing this field of research. Despite this, current knowledge of how communities are structured in terms of species, taxa and functional groups is insufficient. I aim to examine if deterministic assembly rules influence community structure of herbaceous communities. Methodologies will include the use of null models to detect non-random associations at the species, phylogenetic relatedness and functional traits level. I am using a macroecological approach by examining similar ecologically communities with different evolutionary histories in three continents. Experimental work will be conducted to determine if non-random patterns of association are due to increased competition between functionally similar and/or related species. The detection of assembly rules at this scale will have important implications for predicting responses of herbaceous communities to global change, understanding species invasions and community restoration.