Macroscale drivers influencing the structural and functional organization of stream macroinvertebrate metacommunities: potential role of hydrological connectivity

We assessed the potential influence of hydrological connectivity among subdrainages on the structural and functional organization of stream macroinvertebrate metacommunities in 2 adjacent, large Asian watersheds (~1.4 million km2). To examine the structural organization of metacommunities, we used multisite β-diversity partitioning and applied the Elements of Metacommunity Structure (EMS) framework to resolve aspects of taxon associations and metacommunity assembly. We also decomposed functional β diversity into nestedness and turnover to assess functional organization of metacommunities among watersheds of contrasting connectivity. To describe changes in functional composition, we used a multidimensional functional trait analysis to calculate the 3 primary components of functional diversity. The nestedness component of β diversity had a higher contribution in the watershed displaying isolated subdrainages, and apparent lack of hydrological connectivity had a significant effect on the ecological fitting of macroinvertebrate metacommunities, generating a discrete composition of communities. Partitioning of functional β diversity suggested no difference among watersheds in metacommunity functional organization and a high level of functional redundancy among communities of subdrainages independent of hydrological isolation. These results show that hydrological connectivity is potentially an important driver structuring stream macroinvertebrate metacommunities at a macroecological scale. Patterns of metacommunity structure were expressed better using taxonomic than functional-trait diversity. In spite of a perceived functional redundancy, a wider functional space was observed in the absence of hydrological connectivity, a result suggesting discrete but partially overlapping functional entities associated with hydrological isolation in these watersheds.