Latitudinal Patterns And Drivers Of Species Diversity In Montane Forest Communities Of Eastern China

The mechanism underlying the latitudinal diversity gradients(LDG)is one of the most controversial issues in ecology,which is explored in The Origin of Species and included in 125 big questions that Science Magazine published.This study would not only instruct for the conservation of species diversity,but also help us better understand the diverse biodiversity in different regions,such as the asymmetry of species diversity between East Asia with Eastern North America.Although there have been many advances in the study of species diversity,there are still a series of problems to be solved.For example,the effect of evolutionary factors on the pattern of species richness,the latitudinal diversity gradient of different floristic elements and so on.Previous researches have mainly focused on the impact of ecological processes to biodiversity,and the evolutionary causes have been poorly investigated.To date,relative effects of potential environmental and other factors upon the mechanisms of species diversity patterns lack scrutiny.The floristic elements and growth form are two important attributes of community species.The former can reflect the origin,migration and evolutionary history of plants,while the latter involved the different responses to environmental turnovers between woody plants and herbaceous plants.When studying species diversity,fully considering the classification of floristic elements and growth forms can provide a more comprehensive understanding of the LDG mechanism.Here,we used 24 forest communities in eastern China as our sampling sites.In each community,we collected directories and obtained the classified information including plant flora and lifeforms to each plant individual.And then we used correlation analysis and structural equation model analysis to explore the patterns and mechanism of LDG by combining the phylogenetic and climate data for verifying different hypotheses.The main results were summarized as follows.(1)The species diversity and phylogenetic diversity of 24 forest communities graduallydecreased from low latitudes to high latitudes,and the degree of phylogeneticclustering decreased.Phylogenetic ? diversity of 24 forest communities increasedgradually with the increase of spatial and distances.Phylogenetic ? diversityshowed that the effect of environmental distance on phylogenetic ? diversity wasstronger than that of spatial distance.Environmental factors are the main driver ofLDG.(2)The phylogenetic characteristics of temperate floristic elements have a strongerresponse to the environment than tropical floristic elements,which may be relatedto the higher diversification rate.The results of SEM(structural equation modeling,SEM)analyses indicate that the pattern of the species diversity of temperate floristicelements is mainly affected by the diversification rate,while that of tropical floristicelements is greatly affected by environmental factors.Thus,the causes of thespecies richness pattern of differ floristic elements supporting different hypotheses.The temperate floristic elements can be explained by the evolutionary ratehypothesis,while tropical floristic elements tend to support the niche conservationhypothesis.(3)The species diversity and the phylogenetic diversity patterns of woody plants andherbaceous plants were similar along the latitude.Both the diversity patterns weregradually declining from low latitudes to high latitudes.The results of phylogeneticstructure of different growth forms showed that the assemblage processes were notrandom.The phylogenetic structures were clustered in high latitudes,which maymainly be affected by environmental filtering.While the phylogenetic structure inlow latitudes is over-dispersed,that is,the main driver of the construction processmay interspecific competition.There are both clustered and over-dispersedstructures in herbaceous plants,which indicates that environmental filtering andinterspecific competition are the assemblage processes of herbaceous plants.Environmental factors are the main factors affecting the species diversity pattern ofboth woody and herbaceous plants,which can be explained by the nicheconservation hypothesis.In summary,this study combined evolutionary and ecological processes to comprehensively analyze the mechanism of LDG by considering different floristic elements and growth forms of forest communities in eastern China.The results showed that the LDG of forest communities in eastern China is mainly affected by environmental factors,supporting the niche conservative hypothesis.For the temperate folristic elements,the main driver of the gradient pattern was the diversification rate.This study not only helped us to fully understand the mechanism of the LDG from different classification of different floristic elements and growth forms,but also provided a corresponding theoretical basis for the asymmetry of species diversity in East Asia and Eastern North America.That is,higher differentiation rate led to higher species diversity.In addition,this study provided new ideas on the research methods of community phylogeny,such as the division of floristic element and the construction of phylogenetic trees using V.PhyloMaker.