Functional trait dimensions of trophic metacommunities.

Metacommunity ecology currently lacks a consistent functional trait perspective across trophic levels. To foster new cross‐taxa experiments and field studies, we present hypotheses on how three trait dimensions change along gradients of density of individuals, resource supply and habitat isolation. The movement dimension refers to the ability to move and navigate in space, the tolerance dimension addresses the ability to tolerate prevailing environmental conditions and the interaction dimension aggregates the abilities to acquire resources in competition with other species, to defend against consumers or to profit from other species by mutualism and facilitation. In multi‐trophic studies, functionally analogous traits associated to these dimensions need to be defined across taxa and measured. The dimensions represent subnetworks of strongly correlated traits within the overall phenotypic trait network. These subnetworks can be aggregated to trait modules using dimension reduction techniques. We demonstrate how to derive dimensions from species distributions and trait correlation networks, using salt marshes as an example. We hypothesize that at the single‐community scale, investments by organisms in the tolerance dimension increase with decreasing resource supply. Investments to the interaction dimension increase with increasing density. Communities with densely packed individuals are characterized by convergence under equal competition and by increasing divergence under stabilizing and equalizing competition. At the metacommunity scale, trade‐offs between the movement dimension and the interaction dimension shape the community functional composition. Biomass removal by consumers act as an equalizing factor and increase divergence in the interaction and movement dimension, particularly in well‐connected habitats. As future research directions to advance functional metacommunity ecology, we propose investigating 1) the feasibility of using dimensions as broad generalizations of multiple functions in different meta‐ecosystems, 2) functional trait analogues across taxa, 3) dimension responses and effects on gradients of meta‐ecosystems and 4) matching of functionally analogous traits between trophic levels. [ABSTRACT FROM AUTHOR]