Processes structuring macrophyte metacommunities in Mediterranean ponds: combining novel methods to disentangle the role of dispersal limitation, species sorting and spatial scales

Aim: Metacommunity ecology is a vibrant area of research that has received increased attention in recent years, since it provides a framework to assess the underlying dispersal- and niche-based processes that create non-random and ecologically meaningful patterns in species assemblages across the landscape. Here we set out to test for the role of dispersal limitation, species sorting and shared effects in the assembly of pond macrophyte metacommunities across an extensive area within the Iberian Plateau, and to identify which traits, environmental variables and spatial scales are driving local community structure. Location: North-western Spain (Iberian Plateau). Taxon: Pond macrophytes. Methods: We established a novel combination of robust methods capable of identifying the processes and most important landscape scales involved in the assembly of communities. We used metacommunity assembly modelling and multivariate multi-scale codependence analysis (mMCA) to first estimate the relative importance of spatial and environmental effects on community structure, and then to identify significant trait–environment relationships and spatial scales. Results: Analyses showed that the greatest effects were seen for the spatial and mixed spatial and niche-based scenarios, particularly among wind-dispersed species. Thus, dispersal limitation interfered with species sorting in determining assemblage structure by hindering species’ tracking of local environmental conditions. After accounting for this, the metacommunity assembly model revealed that species’ traits were involved in determining abundance structure. mMCA identified the main trait–environment relationships (and spatial scales) as fruit size-nutrient status (~300 km) and growth form-mean pond depth (~250 km). Main conclusions: Our study suggests that dispersal limitation acted in concert with species sorting to influence the community assembly processes underlying selection for particular traits in functional niche space. Accordingly, we emphasize the need to go beyond the traditional taxonomic-based analyses of community composition and the predominant thinking of considering spatial and environmental processes as two alternative and mutually exclusive scenarios of community assembly.