Metacommunity theory is reshaping community ecology but the details of how it can be applied are still emerging. Ecologists have only just started to use metacommunity ideas to understand biological diversity in natural systems. But while metacommunity theory ought to apply naturally to understanding how communities are structured in space, teasing apart evidence of the four metacommunity paradigms (species sorting, mass effects, patch dynamics and neutral community models) has not proved to be simple. Using protists in experimental microcosms, we tested whether spatial heterogeneity in the environment increases metacommunity diversity. We aimed not only to measure effects on diversity but to determine which mechanisms (metacommunity perspectives) allow species to coexist by testing for the effects of resource heterogeneity and dispersal.
We show that increasing spatial heterogeneity in the environment increases the diversity of communities. We identified the metacommunity perspective most responsible for this increase in diversity: mass effects. We also detected evidence of patch dynamics. Notably, baseline diversity was largely determined by non-spatial dynamics. In contrast to recent empirical studies, our evidence for a given metacommunity perspective came from many comparisons (19 in total), most of which were not dichotomous tests for one perspective or another. We expected that using an experimental system would simplify the comparisons necessary to tease out the different metacommunity perspectives. Instead, the ability to ask more precise questions in our system led to an expansion of predictions, rather than a reduction, illustrating the complexity of the metacommunity perspectives and the overlap in their predictions.