Global to community scale differences in the prevalence of convergent over divergent leaf trait distributions in plant assemblages

Abstract

AimThe drivers of species assembly, by limiting the possible range of functional trait values, can lead to either convergent or divergent distributions of traits in realized assemblages. Here, to evaluate the strengths of these species assembly drivers, we partition trait variance across global, regional and community scales. We then test the hypothesis that, from global to community scales, the outcome of co-occurring trait convergence and divergence is highly variable across biomes and communities.Location Global: nine biomes ranging from subarctic highland to tropical rain forest. MethodsWe analysed functional trait diversity at progressively finer spatial scales using a global, balanced, hierarchically structured dataset from 9 biomes, 58 communities and 652 species. Analyses were based on two key leaf traits (foliar nitrogen content and specific leaf area) that are known to drive biogeochemical cycling.Results While 35% of the global variance in these traits was between biomes, only 15% was between communities within biomes and as much as 50% occurred within communities. Despite this relatively high within-community variance in trait values, we found that trait convergence dominated over divergence at both global and regional scales through comparisons of functional trait diversity in regional and community assemblages against random (null) models of species assembly. Main conclusionsWe demonstrate that the convergence of traits occurring from global to regional assemblages can be twice as strong as that from regional to community assemblages, and argue that large differences in the nature and strength of abiotic and biotic drivers of dominant species assembly can, at least partly, explain the variable outcome of simultaneous trait convergence and divergence across sites. Ultimately, these findings stress the urgent need to extend species assembly research to address those scales where trait variance is the highest, i.e. between biomes and within communities.

A fully traits-based approach to modeling global vegetation distribution

“…This analysis builds on previous analyses that showed significant trait convergence (22) for several biomes, which was attributed to environmental differences (16,23,24). These studies also suggest that the functional differences among communities can be conveniently represented by community mean trait values (25).…”

The emergence and promise of functional biogeography

“…As a whole, functional traits can be implemented into more or less complex integrative functions (e.g., CWM is a simple integrative function) to scale up from organs to higher organizational levels including ecosystems and biomes (40,43,44). Traitbased approaches have also been extensively used to describe the diversity of forms and functions within a study unit-often termed functional diversity sensu lato-using different distance metrics (e.g., variance based) (45)(46)(47)(48)(49)(50)(51)(52)(53)(54)(55) and how it scales spatially (56)(57)(58)(59)(60)(61).…”

Latitudinal variation of leaf morphological traits from species to communities along a forest transect in eastern China

“…The larger variance occurring within sites may be the result of micro-site variability, phylogenetic or historical effects, or biotic interactions and competition (Ordonez et al, 2010). This indicates that taking inter-specific differences and site scale (or community-level scale) into consideration is essential for the study of biogeography and the assessment of plant trait variability (Liu et al, 2010;Freschet et al, 2011).…”