Metacommunity structuring in a highly-connected aquatic system: effects of dispersal, abiotic environment and grazing pressure on microalgal guilds

Associating a deconstructive approach with metacommunity ecology brings insights into how biological communities are structured. We examined the effects of dispersal, habitat conditions, and grazing pressure on ecological guilds (i.e., deconstructed entire communities by guilds) of freshwater microalgae. The combination of focus on efficient passive dispersers, an extensive sampling survey, large numbers of abiotic explanatory variables, information on grazing pressure, and characteristics (i.e., high connectivity and areal extent) of the study area enabled us to model roles of various metacommunity processes for guild structure and diversity within guilds. We found that water chemistry, physical habitat, and spatial variables all accounted for rather small amounts of variation in the guild structures. Diversity within each guild generally showed clear spatial patterns independent of local environmental conditions. Wave action and slope of the study sites also affected diversity. Grazing had clear effects on some aspects of diversity. Importantly, the guilds showed significant spatial patterns, suggesting that mass effects occurred at different intensities in our highly-connected study system. The intensity of dispersal was partly related to different dispersal potentials among the guilds. Different traits associated with ecological guilds may hence be associated with dispersal processes detected in systems with high connectivity among sites.