Abstract
The observed patterns and underlying mechanisms of elevational beta-diversity have been explored intensively, but multi-dimensional comparative studies remain scarce. Herein, across distinct beta-diversity components, dimensions and species groups, we designed a multi-faceted comparative framework aiming to reveal the general rules in the observed patterns and underlying causes of elevational beta-diversity. We have found that: first, the turnover process dominated altitudinal patterns of species beta-diversity (βsim > βsne), whereas the nestedness process appeared relatively more important for elevational trait dissimilarity (βfuncsim < βfuncsne); second, the taxonomic turnover was relative higher than its phylogenetic and functional analogues (βsim > βphylosim/βfuncsim), conversely, nestedness-resultant trait dissimilarity tended to be higher than the taxonomic and phylogenetic measures (βfuncsne > βsne/βphylosne); and third, as elevational distance increased, the contradicting dynamics of environmental filtering and limiting similarity have jointly led the elevational patterns of beta-diversity, especially at taxonomic dimension. Based on these findings, we infer that the species turnover among phylogenetic relatives sharing similar functional attributes appears to be the main cause of shaping the altitudinal patterns of multi-dimensional beta-diversity. Owing to the methodological limitation in the randomization approach, currently, it remains extremely challenging to distinguish the influence of the neutral process from the offset between opposing niche-based processes. Despite the complexities and uncertainties during species assembling, with a multi-dimensional comparative perspective, this work offers us several important commonalities of elevational beta-diversity dynamics.
Highlights
Encompassing a large number of endemic and threatened species within extremely limited spaces, montane regions are widely recognized as areas of high priority for conservation [1]
We examined the elevational patterns of standardized beta-diversity, with the aim to assess the dynamics of different deterministic processes as elevational distance increased
The three animal groups were generally consistent on three main points: first, a turnover process dominated the species beta-diversity along an elevational gradient, whereas nestedness process was the main cause for trait-based dissimilarity; second, in the comparison across beta-diversity dimensions, species turnover appeared gradually higher than its phylogenetic and trait-based measures; functional nestedness was relative higher than its taxonomic and phylogenetic analogues; and third, the relative importance of opposite niche-based processes gradually transformed in driving elevational beta-diversity as the elevational distance increases
Summary
Encompassing a large number of endemic and threatened species within extremely limited spaces, montane regions are widely recognized as areas of high priority for conservation [1]. 3. across species groups hypothesis (H0) and potential mechanisms βsim > βsne: species dissimilarity is driven by species replacement resulting from different environment or strong geographical barrier βphylosim > βphylosne: there are strong historical isolation and stable local adaptations for major phylogenetic lineages βfuncsim > βfuncsne: stepwised environmental filtering along elevational gradient acts on highly labile functional attributes βsim > βphylosim/βsne > βphylosne/βsor > βphylosor: species turnover/loss/gain occurs more likely among phylogenetic relatives βsim > βfuncsim/βsne > βfuncsne/βsor > βfuncsor: species turnover/loss/gain frequently occurs among species of similar ecological performance βphylosim > βfuncsim/βphylosne > βfuncsne/ βphylosor > βfuncsor: the traits mediating deterministic and stochastic processes are conserved on phylogeny βant > βrodent > βpasserine (species): lower dispersal efficiency produces higher beta-diversity; invertebrates are more sensitive to the environmental variations than homothermal mammals and birds βant > βrodent/βpasserine (phylogeny): stronger historical isolation will produce a higher rate of phylogenetic dissimilarity. The silhouette images of passerine, rodent and ant were 5 freely obtained from PHYLOPIC (http://phylopic.org/)
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