Effects of multiple dams on the metacommunity structure of stream macroinvertebrates

Dams and floodgates have been established to mitigate flood hazards and to satisfy the growing demand for water resources; however, the excessive presence of dams in river ecosystems causes a series of ecological problems. Most previous studies regarding the effects of dams on aquatic community structure have focused on the effects of individual dams on river ecosystems on a local scale, whereas few studies have investigated the combined effects of multiple dams at the basin scale. In the present study we explored the combined effects of multiple dams on macroinvertebrate metacommunity structure and quantified these effects using variation partitioning and asymmetric eigenvector map analysis. We found that the combined effects of multiple dams on macroinvertebrate metacommunity structure are significant, and that the direct effects of dams that limit dispersal were greater than the indirect effects of changing environmental conditions. We also found that spatial variables at medium and fine scales captured more variation in macroinvertebrate metacommunity structure than broad-scale partitioning. Because broad-scale spatial variations are primarily attributed to environmental spatial structuring, and medium- and fine-scale spatial community structures are likely related to neutral processes, it was inferred that the direct effects of dams were greater than the indirect effects.