Study On Altitudinal And Latitudinal Patterns Of Benthic Algae In Plateau Rivers

Exploring the variation of biogeographic pattern in response to environmental gradient and its potential mechanism is one of the key issues in biogeography.Variation in altitude and latitude are widely recognized biogeographic gradients that profoundly influence multilevel patterns of globle species diversity.However,previous studies on the change in biodiversity distribution pattern with altitudinal and latitudinal gradient mainly focused on terrestrial micro-organisms,and relatively little research has been conducted on macro-organisms,especially aquatic micro-organisms.Moreover,the potential mechanism affecting the geographical pattern of biodiversity was not clear.Exploring the impact of altitude and latitude on the pattern of micro-biodiversity is helpful to improve the understanding of the spatial distribution law of biodiversity,and lay a foundation for predicting the extinction risk of organisms,as well as general law for biodiversity protection under the background of climate change.This study was based on the survey data of benthic algae from four primary tributaries in the upper reaches of Jinsha River,including Heiqu,Xuequ,Ouqu and Sequ.The influence of altitude and latitude on the geographical pattern of species and functional diversity of benthic algae in rivers were explored.Based on the functional characteristics of benthic algae,the variation of altitude and latitude gradients during the benthic algae assemblages,as well as the influence of climatic niche and functional characteristics on the geographical pattern of benthic algae were explored.The main results are as follows:(1)Altitude,latitude and the interactions have significant effects on species richness,β-diversity,turnover and nestedness of benthic algae.Altitude has no significant effect on evenness of benthic algae,and evenness decreaes along the latitude gradient.Altitude and latitude affect benthic algae species diversity in two ways:(1)Altitude and latitude indirectly affect the species diversity of benthic algae by influencing regional climatic variables,(2)Altitude and latitude indirectly affect species diversity of benthic algae by influencing regional climatic variables and then local environmental variables.Altitude and latitude indirectly affect species diversity of benthic algae by influencing different regional climatic variables.(2)Altitude,latitude and the interaction have significant effects on cell size,life form,growth form and guild of benthic algae.Size1 is most sensitive to the variation of altitudinal gradient,while motile is most sensitive to the variation of latitudinal gradient.Altitude,latitude and the interaction has significant effects on functional diversity of benthic algae.Altitude and latitude indirectly affect functional diversity of benthic algae by influencing different regional climatic variables.The mechanism by which altitude and latitude affect species diversity and functional diversity of benthic algae is similar.(3)The distribution of different functional traits of benthic algae along altitude and latitude gradients is influenced by different community assembly mechanisms.The cell size of benthic algae is randomly distributed along the altitudinal and latitudinal gradients.The life form and growth form of benthic algae change from convergence to divergence along the altitudinal gradient,and from convergence to divergence to convergence along the latitudinal gradient.The guild of benthic algae distribute randomly along the altitudinal gradient,and change from convergence to divergence along the latitudinal gradient.Chemical oxygen demand is the most important environmental variable that affects the convergence or divergence of cell size of benthic algae.Dissolved oxygen is the most important environmental variable that affects the convergence or divergence of life form of benthic algae.Turbidity is the most important environmental variable that affects the convergence or divergence of growth form and guild of benthic algae.The convergence or divergence of functional traits of benthic algae along the altitudinal and latitudinal gradients supports the stress-dominance hypothesis.(4)Regional occupancy and local abundance of benthic algae were significantly and positively correlated.Climatic niche position is the most important variable affecting the regional occupancy and the local abundance of benthic algae.The functional traits of benthic algae have little effect on the regional occupancy and the local abundance,which is smaller than that of the climatic niche position.The effect of functional traits of benthic algae on local abundance is greater than the effect on regional occupancy.And the functional traits of benthic algae have greater impacts on the local abundance than on the climatic niche breadth.Due to the double threats of low regional occupancy and low local abundance,benthic algae species located in marginal climatic niche position are more sensitive to climatic change and more vulnerable to extinction in the context of global climatic change.