Environmental Heterogeneity-species Richness Relationships In China

The environmental heterogeneity hypothesis is one of the core pillars of ecological theory.Areas with high environmental heterogeneity have more diverse habitat types and more available resources,which in turn promote the coexistence of more species by providing a wider ecological niche.Therefore,environmental heterogeneity can have important effects on the formation,maintenance and coexistence of species.However,previous studies on the relationship between environmental heterogeneity and species richness usually only focus on individual environmental heterogeneity factors,and few studies have explored the relationship between environmental heterogeneity and species richness by combining different environmental heterogeneity factors at different spatial scales,which may lead researchers to ignore some environmental heterogeneity factors that may have an important impact on species richness,and draw relatively one-sided conclusions.The distribution pattern of species richness and its causes depend on the research object,and there is still a lack of research and discussion on different species groups under the same temporal and spatial conditions,which is not conducive to our in-depth understanding of the universality of biodiversity distribution patterns.In addition,the impact of environmental heterogeneity on species richness is usually constrained by climate,and there is still a lack of research on how climate affects the relationship between environmental heterogeneity and species richness in China.Therefore,this study used the distribution data of angiosperms in China with a resolution of 100 km×100 km and the distribution data of higher plants,mammals,birds,reptiles and amphibians at the provincial scale,and explored the relationship between environmental heterogeneity and species richness at the national and regional scales,combined with different categories of environmental heterogeneity factors,climate factors and human activity factors.The main research results are as follows:(1)There are strong and weak correlations between different environmental heterogeneity factors(r:-0.83～1;median:0.22;mean:0.26).Temperature(TEM),potential evapotranspiration(PET),and elevation(ELEV)heterogeneity were strongly correlated(average r=0.60);Precipitation heterogeneity was less correlated with other environmental heterogeneity components(average r=0.33);Soil heterogeneity had the lowest correlation with other environmental heterogeneity components(average r=0.18).Net primary productivity heterogeneity and vegetation height heterogeneity were highly correlated(average r=0.61);in addition,the strongly correlated environmental heterogeneity factors had similar spatial distribution patterns.It shows that the magnitude of the correlation between environmental heterogeneity factors depends on the variable category and calculation method used to calculate environmental heterogeneity.(2)Different environmental heterogeneity factors have different effects on the species richness of different species groups.At the provincial scale,the results of the univariate linear regression model:for higher plants,the net primary productivity standard deviation(NPP.sd)has the highest interpretation rate(R~2=0.52),followed by the precipitation range(PRE.ra)(R~2=0.49);For mammals,plant species richness(PLA)has the highest interpretation rate(R~2=0.66),followed by potential evapotranspiration terrain ruggedness index(PET.tr)and temperature terrain ruggedness index(TEM.tr),with R~2 of 0.51 and 0.51,respectively;For birds,PLA has the highest interpretation rate(R~2=0.74),followed by NPP.sd(R~2=0.58);For amphibians,PLA has the highest interpretation rate(R~2=0.55),followed by net primary productivity range(NPP.ra)(R~2=0.51);For reptiles,NPP.ra,NPP.sd and PLA had the highest explanatory power with R~2 of 0.59,0.57 and 0.57,respectively.It shows that climate heterogeneity,vegetation heterogeneity and landcover heterogeneity have important effects on the species richness of different species groups.(3)This study proposes a conceptual framework for the influence of climate on the relationship between environmental heterogeneity and species richness:the influence of climate on the relationship between environmental heterogeneity and species richness has two different paradigms:one is gradual,that is,the impact of environmental heterogeneity on species richness decreases with the increase of climate stress;Another is abrupt,that is,there is a climatic threshold for the response of species richness to environmental heterogeneity.At the threshold,the impact of environmental heterogeneity on species richness will suddenly decrease or increase.(4)Combining the results of regression tree model,random forest model and variation partitioning of angiosperm species richness:when annual precipitation(MAP)<255.3 mm,precipitation seasonality(PSN)is the most important factor affecting angiosperm species richness,and climate variables had the highest explanation rate(38.7%);when MAP<688.4 mm and≥255.3 mm,the regression tree was divided into two branches with the environmental heterogeneity PC1 axis(the first axis of the principal component analysis)as the node,and the standard deviation of net primary productivity(NPP.sd)is the most important influencing factor,and the environmental heterogeneity variables had the highest explanation rate(57%);when MAP≥688.4 mm,the regression tree is divided into two branches with the environmental heterogeneity PC1 axis as the node,and the net primary productivity terrain ruggedness index(NPP.tr)was the most important influencing factor,and the environmental heterogeneity variables had the highest explanation rate(64%).These three regional boundaries largely coincide with precipitation lines commonly used to delineate climatic regions(arid,semi-arid and sub-humid,and humid).The above results show that in arid regions,environmental heterogeneity has a weak effect on angiosperm species richness;in non-arid regions,environmental heterogeneity has a strong and similar effect.(5)In the Yellow River Basin,the results of tree regression model and multiple regression:For angiosperms,the temperature seasonality(TSN),precipitation seasonality(PSN)and vegetation height range(HEI.ra)were the most important factors;For vertebrates,temperature seasonality(TSN)and net primary productivity range(NPP.ra)were the most important factors.The results indicate that species richness is determined by environmental heterogeneity and climate in the Yellow River Basin.(6)The above research results at different spatial scales show that the effects of environmental heterogeneity and climate on species richness are scale-dependent:With the increase of spatial grain size,the influence of vegetation height heterogeneity,precipitation heterogeneity and climate on plant species richness is weakened,while the influence of topographic heterogeneity on plant species richness is strengthened.In general,this study selected different environmental heterogeneity factors to comprehensively explore the relationship between environmental heterogeneity and species richness in China at different spatial scales,and elaborated the general paradigm that how climate affect relationship between environmental heterogeneity and species richness.The variable category and calculation method used to calculate environmental heterogeneity used to calculate environmental heterogeneity,spatial scale and biological groups will all affect the relationship between environmental heterogeneity and species richness in China.