Traits patterns indicate that changes in productivity and geographic isolation will impact functional diversity in the alpine

Background/Question/Methods Understanding the roles of resource availability and dispersal in structuring plant communities has been central to the study of ecology. Naturally occurring gradients have proved useful in exploring these factors. Our objective was to examine trait patterns along gradients of productivity and geographic isolation and to relate these results to the processes suggested to affect species coexistence. We analyzed trait patterns in areas of alpine tundra that differed in productivity which relates to the role of resource availability, and geographic isolation which relates to the role of dispersal. We hypothesized that 1.) as productivity increases, coexisting species within a site would have less similar traits, suggesting an increased role of competition, and 2.) with greater geographic isolation, there would be greater divergence among sites, suggesting a decreased role of dispersal. We sampled species and trait composition in 81 1m² plots along a productivity gradient at 1 site, and across 17 sites varying in geographic isolation. To assess productivity we sub-sampled plots for aboveground biomass. To quantify geographic isolation we calculated the area of alpine around each site. For all species, we measured traits associated with resource use and capture: specific leaf area, height, stomatal conductance, chlorophyll content, and leaf succulence.

Results/Conclusions We found that coexisting species within a site differed more in their traits at higher productivity, indicating that the strength of competitive exclusion may increase with increasing productivity. Additionally, we found greater divergence among isolated sites suggesting that dispersal does not counteract the effects of competition at higher geographic isolation, but may counteract some competitive exclusion when there is greater connectivity between sites. Currently many systems are threatened by habitat fragmentation which increases geographic isolation and changes in climate and nitrogen-availability which alter productivity. Our results suggest that changes in productivity associated with global change may lead to stronger competitive exclusion which may lead to the loss of rare or subordinate species. Additionally, dispersal may not be able to counter these effects if geographic isolation increases as a result of habitat fragmentation. Our results suggest that global change factors will likely interact and have strong impacts on the functional diversity of plant communities.