Changes in trait divergence and convergence along a productivity gradient in wet meadows

Ecological theory predicts that species coexisting locally may either be functionally more dissimilar than expected by chance due to niche differentiation ('trait divergence'), or rather be functionally similar given that species bearing traits associated with low competitive ability are likely to be excluded ('trait convergence'). How the importance of trait divergence and convergence varies with productivity and depending on different plant traits still remains controversial. However assessing the effect of site productivity on meadow species assembly can help defining proper management practice for these ecosystems. We sought evidences for trait convergence and divergence across a productivity gradient over 21 wet meadows in Zelezne hory Mts. (Czech Republic), considering 13 plant traits. In each meadow, we recorded species composition in four 1 m(2) plots divided into 100 subplots, and different environmental parameters and site characteristics linked to productivity (standing biomass, soil water table and soil nutrients content). Species spatial aggregation within plots (calculated by the V-score metric on the 100 subplots per plot averaged across all plots in each meadow) was correlated with trait dissimilarity between species in a rather limited number of cases. Significant divergence was observed when traits were considered in combination or when using phylogeny as a proxy of functional similarity. Moreover, plot level patterns of trait divergence and convergence depended on local environmental characteristics. Specifically, for several of the traits studied (e.g. lifespan, combined traits) there was evidence that functional divergence of species decreased with increasing productivity. Overall from these results at fine scale we cannot rule out neutrality, but, where significant, patterns suggest stronger effects of niche differentiation between coexisting species (trait divergence) rather than convergence of functionally similar species. Nevertheless our results also support the view that increased productivity, coupled with intense competition for resources (mainly for light), can lead to the coexistence of more functionally similar species. This is relevant because biodiversity enhancement is generally achieved by maintaining low productivity in these meadows. In general our study gives insights on how species-coexistence is related to life history traits and environmental variation, which is also relevant for the conservation and management of species-rich meadows. (C) 2013 Elsevier B.V. All rights reserved.