It is lonely at the top – patterns in elevational diversity among micro- and macroorganisms

Background/Question/Methods

Data and analyses of elevational gradients in diversity have been central to the development of a range of general theories of biodiversity. Elevational diversity patterns have, however, been severely understudied for unicellular organisms. Our aim was to examine elevational gradients in the alpha and beta diversity of macroinvertebrates, diatoms and bacteria along a stony stream in China that covered a large elevational gradient. Study stream was affected by humans only at low elevations and stream was in pristine state at higher elevations.

Results/Conclusions

We found that bacterial richness followed an unexpected monotonic increase with elevation. Diatoms decreased monotonically and macroinvertebrate richness showed a clear unimodal pattern with elevation. The unimodal pattern for macroinvertebrates was best explained by the mid-domain effect (r² = 0.72). Bacteria showed the lowest elevational turnover rate of the three taxa across all pairwise sites. Turnover rates were overall comparable at the pristine and human-impacted sites, yet community compositions differed substantially between the two site groups for all taxa.

We conclude that the patterns in elevational alpha diversity differed substantially among the three studied multi-trophic groups comprising unicellular and multicellular aquatic taxa. Our results further indicated that the patterns in beta diversity were scale-dependent, turnover was lowest for bacteria and that human impacts on species turnover rates were confounded with environmental and spatial variables.