Does the importance of environmental and spatial variables in structuring stream macroinvertebrate metacommunities depend on dispersal mode?

Background/Question/Methods

The metacommunity concept has been increasingly applied when studying the regulation of biodiversity. A metacommunity refers to a set of local communities connected by the dispersal of multiple interacting species. Within a metacommunity, variation in local community structure is affected by variation in local environmental characteristics and the spatial arrangement of the sites. Organisms with contrasting dispersal modes are likely to respond differently to these factors. Poorly dispersing organisms are expected to be constrained by the spatial distances between sites. Conversely, the effectively dispersing organisms (as being better able to track environmental heterogeneity) should be relatively more affected by the local environmental characteristics. We studied how dispersal mode affect the relative effects of local environmental conditions and spatial location on the structure of stream macroinvertebrate metacommunities. We sampled macroinvertebrate communities in three drainage basins in Northern Finland and assigned organisms into three dispersal mode groups: passively dispersing species with aquatic adults, passively dispersing species with terrestrial adults and actively dispersing species with terrestrial adults. Spatial variables were generated using Principal Coordinates of Neighbor Matrices based on both overland and watercourse distances. The relative importance of the local environmental variables and spatial variables was analyzed using partial Redundancy Analysis.

Results/Conclusions

In general, the importance of environmental structuring was always more important compared to spatial structuring suggesting that local environmental conditions mainly structure the macroinvertebrate communities in headwater streams. This finding is in line with several other recent studies on stream macroinvertebrates and many other organism groups. The importance of both environmental and spatial components varied for different dispersal mode groups. However, results varied considerably between the three basins and thus no consistent pattern was observed regarding our expectations. Across-basins analysis revealed, as was also expected, that environmental structuring was strongest for the group of species with terrestrial winged adults and spatial structuring (i.e. dispersal limitation) for the group of species with aquatic adults. No consistent differences between the results based on watercourse distances and overland distances were observed. Our results emphasize that metacommunity structuring may be strongly region and scale specific, and thus inferences from studies relying only on one region should not be extrapolated to other regions.