| Unraveling the proportional strength of environmental screening and spatial processes in shaping biological communities is a key focus of meta-community ecology,which is one of the rising subjects of community ecology and constitutes an important paradigm for investigating community assembly processes.In many river ecosystems,benthic macroinvertebrates have been widely studied,whereas alpine streams have received less attention in meta-community ecology.The overall objective of this study was to better develop our understanding of macroinvertebrates' biodiversity patterns and to examine the relative effects of spatial and local environmental determinants that regulate stream macroinvertebrate meta-community composition in the alpine streams located in the Baima Snow Mountain,Southwest China.The environmental characteristics and community data were collected from 35 sites(study-1)and 9 sites(study-II,in 3 year period)distributed in alpine streams along the Yangtze river using different strategies both in the field and laboratory.Multiple replicates(n=5)of macro invertebrate samples were collected employing a Surber net(500 ?m,mesh size,30 X 30 cm).All the macroinvertebrates specimens were subsequently classified and identified,generally to genus and probably to morpho-species level.Moreover,the environmental drivers,including conductivity,water temperature,oxidation-reduction potential,total dissolved solids,dissolved oxygen,and pH were calculated in situ,while the remaining drivers such as total nitrogen,total phosphorus,salinity,dissolved organic carbon,nitrate,ammonia,total organic carbon,and dissolved silicon concentration gradients were determined in the laboratory.The spatial extent and altitudes of each sampling site were identified through a GPS appliance(Garmin eTrex20,China).The Flow Globe(FPI01,Global Water)was used to measure flow velocity,and turbidity employing turbidity meters(SGZ-200BA,China),and the stream's width was calculated with a common tape,as well as land use characteristics and spatial determinants were examined.The community and environmental matrices,as well as the richness and diversity indices,were analyzed using different multivariate analyses.The forward selection algorithm was used to maintain the significant set of local environmental(including landuse variables)and spatial determinants for constrained ordination models.Using redundancy analysis and variation partitioning,we evaluated the significance of spatial and local environmental characteristics in the meta-community organization.A total of 17,823 macroinvertebrates individuals were sampled and classified,with 73 taxa,representing 3 phyla,6 classes,12 orders,and 47 families,with Baetidae being the most dominant family in both the periods 2017 and 2019 and Tubificidae in 2018.Alpine stream insects composed 86.05%,followed by Clitellata(13.28%),Malacostraca(0.39%),Rhabditophora and Arachnida(0.10%),and Entognatha(0.04%).The results showed conspicuous differences in the macro invertebrate community composition across periods.Besides,the findings revealed that both environmental filtering and spatial processes jointly shape the configuration of macroinvertebrate meta-community,while their respective contributions to community structure changed throughout periods.In most scenarios,the Redundancy Analysis(RDA)and variation partitioning approach demonstrated that local environmental characteristics were highly influential drivers of community structure,whereas spatial factors also played a substantial influence.Further,the study showed that the explanatory accuracy,identity,and relative strength of assembly processes altered throughout periods.In particular,the results showed that high-influence environmental filtering was identified in determining community assembly in both the 2018 and 2019 sampling periods,implying that deterministic mechanisms prevailed in controlling community dynamics in the analyzed stream during these periods.Conversely,we also determined that spatial characteristics have a higher influence on meta-community organization in the period 2017,reflecting prominent dispersal mechanisms that may be due to higher site connectivity.Therefore,we concluded that the structure of the alpine stream macroinvertebrate metacommunity could be driven by the combination of environmental filtering and spatial dynamics,with the relative strength fluctuating throughout periods.Thus,the community ecology research in water systems should not be limited only to a single snapshot examination,based on these findings.In addition,a large number of benthic species are reactive to habitat perturbation,particularly,Ephemeroptera species(mayflies)are among the most susceptible groups of insects.Although they are vulnerable to environmental alteration,knowledge pertaining to their species diversity is still limited in many alpine streams.In particular,we also objective to better develop our understanding of the Ephemeroptera assemblages and the impact of physicochemical factors on this particular group of aquatic insects in the alpine streams.The results revealed that the community structure of Ephemeroptera species was different across the streams.In terms of relative abundance,Baetiella margwata and Baetis sp.were the most prevalent Ephemeropterans,accounting for more than half of the discrepancies between the streams.Virtually all sites in the Yeri stream maintained fairly good quality settings for many Ephemeroptera species,as illustrated by the maximum richness and diversity followed by Benzilan,while a relatively poor assemblage was found in theSharong stream.These differences could be the result of higher environmental variability found between the streams.Particularly,the RDA model showed that altitude,water temperature,total dissolved solids,silicon,conductivity,and pH characterized the majority of the difference in species structure among the several environmental parameters analyzed.However,altitude alone accounted for 17.74%of variations in species composition,and further comprehensive analysis validated its considerable influence on diversity measures.Future studies should concentrate on determining the magnitude of threats and stress to this significant group of organisms in alpine stream habitats,particularly the implications of large-scale human disruption.Besides,consistent stream quality surveillance in aquatic ecosystems is essential to investigate further their ecological status in the face of habitat deterioration and water contamination. |
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