Spatial Pattern And Metacommunity Assembly Of Macroinvertebrates In The Huai River Basin

Series local communities,which are connected by species dispersal,are usually called metacommunity.Traditionally,the local habitats in a metacommunity are not directly connected except through the dispersal of organisms.However,the conventional concept of metacommunity can be challenged by dendritic river networks combine characteristics.River network are strong hierarchy and asymmetry due to their dendritic branching architecture and flow direction.Here we analyze the metacommunity structure of macroinvertebrate in the upper and middle reaches of Huai River Basin,which is a typical plain river network region with many dams,and evaluate the influence of local environmental factors;dendritic structure of river network;and combined effects of many dams on by using different spatial eigenfunction models and variation partitioning.The results indicated that:(1)There was a lower diversity index of macroinvertebrate community in the upper and middle reaches of Huai River Basin.It is found that Oligochaete and Chironomidae,as representative of pollution-resistance species,were the chief dominant species in the study area;while species intolerant to organic-rich and polluted areas,such as Ephemeroptera,Plecoptera and Trichoptera were rarely found.The phenomenon showed that the eco-environment condition of the study region was seriously polluted,which resulted in growing abundantly of pollution-resistance species and reducing sensitive species,therefore the biodiversity was driven to lower levels.Based on the index of community similarity,four types of macroinvertebrate community were identified.Indicator taxa in each type of the four groups were found and the percentage of the five functional feeding groups showed significant differentiation among the different groups at the same time.All this indicated that there were obviously spatial patterns of macroinvertebrate community in the study region.(2)The river network structure had significant effects on macroinvertebrates metacommunity assembly.However,spatial variables derived from the stream distance din not captured much more variation of macroinvertebrates community in stream networks than those based on the overland distance as expected,which probably occurred for the reasons that there are many dams in the Huai River Basin,and the connectivity of river was decreased.Furthermore,we found spatial models incorporated flow direction captured the least spatial variation of macroinvertebrates metacommunity.It might be because that the Huai River Basin belongs to a plain river network and the current direction is not very obvious.We found the spatial molds based on watercourse distance with direction accounted for smaller spatial scales of variation in community structure than the simpler Euclidean or symmetrical stream distances.Although,stream distance and overland distance captured much more variation of community than asymmetric stream distance,it cannot be inferred that dispersal ability of macroinvertebrate through stream distance and overland distance are higher than downstream dispersal.Because larger scale spatial structure(i.e.the scales EMEM,SMEM best accounted for)may be largely attributable to environmental spatial structuring,whereas smaller scale spatial variation(AEM)may be related to species dispersal processes.(3)Environmental variables exhibited large spatial variation in the study area.The results of redundancy analysis between environment and community composition showed that environmental variables significantly explained community variation,Total nitrogen,ammonia,transparency,mean annual temperature and habitat scores were identified as the key variables for macroinvertebrate community.However,based on the variation partioning analysis results between environmental process and spatial process,a large part of environmental effects(almost 25%-80%of total explained variation by environmental factors)were mixed by spatial effects.After the removal of space effect,explanatory power of every measured environmental variable for macroinvertebrate community was decreased and total nitrogen,transparency,and mean annual temperature were still considered as the key variables for influencing macroinvertebrate metacommunity.(4)Dams have impacts on community structure of macroinvertebrates in river ecosystem.On the one hand,dams can directly affects macroinvertebrates metacommunity through hampering macroinvertebrate dispersal;while on the other hand,it can also indirectly influence macroinvertebrates metacommunity by changing environmental variables.The study found that the observed pure dam effect on macroinvertebrates metacommunity was much higher than that shared with environmental effect,which indicated direct effects of dams on macroinvertebrate metacommunity might be greater than indirect effects of that.We furthermore found that more spatial variation of macroinvertebrate metacommunity at medium and fine scales were captured than broad scales.Because broad scales spatial variation are mainly attributed to environmental spatial structuring,while medium and fine scales spatial structure of community primarily relates to neutral process,Therefore,the discovered impacts of dam on macroinvertebrate metacommunity mainly be affected by dispersal process in which dam was considered as barrier,while relatively little effect was related to environmental spatial structuring.According to these researches,it is concluded that Oligochaete and Chironomidae,as representative of pollution-resistance species,were the chief dominant species in the study area;while species intolerant to organic-rich and polluted areas,were rarely found.There were obviously spatial patterns of macroinvertebrate community in the study region.Stream distance and stream distance with direction captured much more spatial variation of macroinvertebrate metacommunity,which indicated that river network structure had significant effects on macroinvertebrate metacommunity assembly.And meanwhile,we found environmental variables significantly explained macroinvertebrate metacommunity variation,but a large part of environmental effects(almost 25%-80%of total explained variation by environmental factors)was confounded by spatial patterns.For a typical plain river network region with many dams,the discovered impacts of dam on macroinvertebrate metacommunity mainly be affected by dispersal process in which dam was considered as barrier,while relatively little effect was related to environmental spatial structuring.