Metacommunity Assembly Mechanisms Of River Zoobenthos Based On Different Dispersal Capacity

The community assembly mechanism has always been the core content of community ecology research.With the proposal of the concept of metacommunity,the correlation between community structure and environmental factors and spatial processes is considered in a novel way,which provides a good idea and method for community assembly.Biological dispersal is one of the most important processes in biogeography and ecology.It plays an important role in judging the relative importance of environmental filtration and spatial processes in the construction of metacommunity.However,direct measurement of dispersal capacity is very difficult.There has been a lack of quantitative indicators of comprehensive dispersal capacity covering all models.Therefore,in terms of metacommunity,there is little research on biological dispersal capacity,but it is of great significance to explore the mechanism of community assembly from this perspective.The mechanism of metacommunity assembly will vary with factors such as study area,study object,and study time.Compared with terrestrial and marine ecosystems,river ecosystems have many unique physical characteristics.The impact of these special structures on dispersal may be the most important factor in assembly river metacommunity,and thus has become an ideal model to verify metacommunity.As an important part of the aquatic ecosystem,zoobenthos have rich dispersal patterns and become excellent research objects.The study area selected in this study is the Shahe River system of the Shaying River Basin,and the research object is zoobenthos.Biological samples are collected and environmental variables are carried out in three hydrological periods representing the northern subtropical zone affected by the monsoon:the intermediate season,the wet season,and the dry season.Based on a detailed analysis of the zoobenthos dispersal capacity,the purpose of this study is to use the dispersal capacity as a grouping factor,and environmental factors and spatial factors as covariates to explain the metacommunity structure of zoobenthos in the dendritic network river system so as to provide a theoretical basis for the restoration of river ecosystem and the protection of aquatic biodiversity.The results show that:(1)In this study,53 species of zoobenthos in 40 families,3 phyla were recorded in Shahe River system,including 6 species of Annelida,4 families(11%),30 species of Arthropoda,25 families(57%),17 species of Mollusca,11 families(32%).The spatial variation and mean values of benthic animal density were as follows: dry season > intermediate season > wet season.Except that Arthropoda dominated the dry period,Mollusca dominated the other two periods.The spatial variation amplitude and average value of benthos biomass are as follows: wet season > intermediate season > dry season,which showed an opposite trend to the density change.The proportion of biomass in three hydrological periods is the largest in Mollusca.The Shannon-Weaver diversity index of zoobenthos in Shahe River system is low,showing a trend of large differences among sample points,but the seasonal differences are not significant.(2)All the collected species were classified into three dispersal groups: Weak dispersers,Medium dispersers and Strong dispersers according to their dispersal ability values.Among them,27 species were Weak dispersers,such as Branchiura sowerbyi,Bellamya purificata and so on.There are 16 species of Medium disperser,such as Chironomus sp.There are 10 species of Strong dispersers,such as Ephemera sp.,Limnophilus sp.,etc.It can be found that the weak dispersers of Shahe river system are in the majority,indicating that Shahe river system is in a stable recovery period after water ecological management.There are significant differences in the spatial distribution of three dispersal groups of zoobenthos in Shahe River system.On the whole,the zoobenthos with strong dispersal ability are more likely to appear at the source,and the medium and weak dispersers are present at all positions of the river.The seasonal difference shows that the proportion of the strong dispersers in wet and dry season is higher than that in the intermediate season,and the species with weak dispersal ability are mostly distributed in the different points in the intermediate season.There are significant differences in the dispersal ability of all kinds of points,and the points with higher dispersal ability appear in the upstream area,which is related to the quality of the upstream habitat.It is considered that the interference is light,and the seasonal differences of the dispersal ability of the sample points are not obvious,which indicates that the local community structure is relatively stable.(3)In the three hydrological periods,environmental factors,PCNM spatial factors simulating the terrestrial dispersal of zoobenthos,and AEM spatial factors simulating the directional dispersal along the river channel all affected the metacommunity structure of zoobenthos in the Shahe River system.The explanatory power of spatial factors(AEM or PCNM)is stronger than that of environmental variables.which is expressed as follows: in the intermediate season,the AEM variable alone explained the most community variation.It may be because the hydrological environment is stable and the organisms can fully dispersal along the river network,so the river network distance has a relatively greater effect;During the wet season,pure PCNM variables have the largest interpretation of community variation.It is presumed that due to highflux currents and seasonal flood events,which connected the previously unconnected habitats,resulting in obvious land dispersal;In the dry season,the community variation explained by AEM and PCNM variables alone is significant,which may be speculated to be caused by the low water flow in the dry season,resulting in partial dryness of the river network,decreased river connectivity,and limited dispersal.Therefore,the two models that simulate dispersal play a more significant role in community construction and formation.(4)Using the strength of dispersal capacity as a grouping factor,the impact of dispersal on the structure of the metacommunity is discussed in detail.The results showed that environmental factors and two groups of spatial factors could affect the community structure of zoobenthos,but the relative effects of environmental and spatial factors were different among the dispersal groups.The explanation rate of spatial factors to weak dispersers is higher than that of environmental factors.On the contrary,the community structure of the strong dispersers is more affected by the environmental filtration.Moderate dispersers show that both environmental and spatial factors are important.