Partitioning spatial, environmental, and community drivers of ecosystem functioning

Context: Community composition, environmental variation, and spatial structuring can influence ecosystem functioning, and ecosystem service delivery. While the role of space in regulating ecosystem functioning is well recognised in theory, it is rarely considered explicitly in empirical studies. Objectives: We evaluated the role of spatial structuring within and between regions in explaining the functioning of 36 reference and human-impacted streams. Methods: We gathered information on regional and local environmental variables, communities (taxonomy and traits), and used variance partitioning analysis to explain seven indicators of ecosystem functioning. Results: Variation in functional indicators was explained not only by environmental variables and community composition, but also by geographic position, with sometimes high joint variation among the explanatory factors. This suggests spatial structuring in ecosystem functioning beyond that attributable to species sorting along environmental gradients. Spatial structuring at the within-region scale potentially arose from movements of species and materials among habitat patches. Spatial structuring at the between-region scale was more pervasive, occurring both in analyses of individual ecosystem processes and of the full functional matrix, and is likely to partly reflect phenotypic variation in the traits of functionally important species. Characterising communities by their traits rather than taxonomy did not increase the total variation explained, but did allow for a better discrimination of the role of space. Conclusions: These results demonstrate the value of accounting for the role of spatial structuring to increase explanatory power in studies of ecosystem processes, and underpin more robust management of the ecosystem services supported by those processes.