Effects Of Riverine Topological Structures On Metapopulation Persistence

Both climate change and anthropogenic disturbance have accelerated the degradation of natural ecosystems,especially in complex watershed ecosystems where aquatic species are facing a huge threat to their survival.As the habitat of aquatic species,riverine ecosystems have a unique dendritic structure,which can strongly affect the ecological dynamic process of aquatic species.Despite years of attention by ecologists,the dynamics of species constrained to disperse within riverine networks are not well captured by existing population models due to the spatial riverine topological complexity.Based on traditional metapopulation theory,we construct a new theoretical framework for riverine metapopulation,by incorporating local colonization-extinction process and regional dispersal characteristics.With numerical simulations,we firstly investigate the effects of variation in branch size,branching probability and network size on riverine metapopulation persistence at steady state.Then we apply this model to the six sub-basins in Yangtze River Basin,including Yalongjiang,Mintuojiang,Jialingjiang,Hanjiang,Dongting Lake and Poyang Lake,in order to make a systematic comparative analysis of the persistence of species with different dispersal traits among these six sub-basins.With numerical simulation,we find that:(1)At relatively high species extinction rates,increasing variation in branch size can significantly promote species survival,theoretically demonstrating that previous studies ignoring variation in branch size might have overestimated species extinction risk.(2)Two-way dispersal is not always an optimal strategy for metapopulation persistence relative to one-way dispersal(e.g.,upstream or downstream dispersal),determined by species relative extinction rate.(3)When considering the interactive effects of up-and down-stream dispersal,we find that moderate upstream-biased dispersal maximizes metapopulation viability.At the same time,the hierarchical level of the largest branch can dominate species persistence.(4)Increasing riverine network complexity can increase species survival.More specifically,increasing branching probability and network size both can promote species persistence,more obviously for branching probability.(5)By comparing six sub-basins in Yangtze River Basin,we find that species can persist more easily in Poyang Lake Basin with a more complex riverine structure than other sub-basins,while species in Yalong River basin with a relatively simple riverine structure go extinct easily,further confirming our modelling predictions.Overall,our theoretical outcomes demonstrate that both riverine structural complexity and species dispersal traits jointly determine riverine metapopulation persistence,and thus reveal the underlying ecological significance of riverine topological structures,thereby offering scientific theoretical basis and decision support for aquatic species conservation and management.