Species richness of limestone grasslands increases with trait overlap: evidence from within‐ and between‐species functional diversity partitioning

Summary1. Considering both within- and between-species functional diversities in plant communities hasbeen recently suggested as a way to understand potential assembly mechanisms that control speciescoexistence. In particular, relating variations in species richnessto within- and between-species func-tional diversities can provide a useful framework for evaluating the importance of alternative com-munity assembly theories. In addition, little is known about whether the relationship betweenspecies richness and functional diversity components arises from direct or indirect effectsof theabiotic environment.2. We tested the relationship between functional diversity and species richnessby disentanglingfunctional diversity components into within-species, between-species and total functional diversitiesand by considering potential direct and indirect effectsof the abiotic conditions. Multi- and single-trait approaches were applied using three key plant functional traits (height, specific leaf area(SLA),LDMC). Traits were measured on species coexisting across sixteen species-richlimestone grass-lands. Direct and indirect effectsof the abiotic conditions were evaluated using multiple soil proper-ties including heterogeneity in soil depths.3. The within-species functional diversity ranged between 13.5% and 33.6% of the total functionaldiversity. Within-species diversity was the main functional component linked to variations in speciesrichness, despite the within-species functional diversity being lower than between-species functionaldiversity. Environmental soil properties had a direct effect on species richnessbut did not affectfunctional diversity components.4. Synthesis: Our results provide evidence that increasing the trait overlap between species, due toan increase in within-species diversity, may relate to greater species coexistence. Disentangling mul-tiple functional diversity components indicated that there may be equalizing mechanisms that act aspotential drivers of species coexistence. In addition, it suggests the possibility that this approachmay provide a better understanding of the processes involved in the structure of plant communities.Key-words: abiotic environment, assembly rules, determinants of plant community diversity andstructure, functional diversity, single- and multi-trait approaches, species richness, trait overlapIntroduction