Contrasting richness patterns of exotic vs. native species along elevational gradients

Background/Question/Methods

Most studies on distribution and diversity patterns related to elevation have been performed on native species. The corresponding patterns for exotic species remain largely elusive.  Furthermore, both climate-change related warming and exotic invasions along elevational gradients are likely to impact the distributional patterns of native species.  Here, we compiled and analyzed published datasets from 80 case studies on elevational distributions of exotic species (of both plants and animals) around the world.  We then compared these results with results from 443 case studies on native species (Guo et al. Global variation in elevational diversity patterns. Sci Reports 3: 3007. 2013) in order to determine whether or not exotic species exhibit similar elevational patterns (e.g., unimodal) as native species. We hypothesized that across the world’s mountains that exotic species largely remain concentrated at lower elevations than native species, and that both increased invasions and the expansion of these invasions to higher elevations will push native species to higher elevations in the future.

 Results/Conclusions

We found that exotic species are, for the most part, distributed at lower elevations than native species.  The richness of exotics species also peaked at lower elevations than did that of native species.  Relative to native species, the distributions of exotic species in relation to elevation were less unimodal, and instead, more negative.  This is likely due to the fact that exotic species typically share stronger associations with human population and activities occurring at lower elevations than do native species.  Although we realize that these observations are just a snapshot of many ongoing, long-term invasion processes, these findings offer valuable insights. For example, our finding suggest that exotic invasions and climate change-related warming may jointly push native species to higher elevations, further reducing their already shrinking habitats.  Therefore, to better facilitate native species conservation and exotic species management, long-term, detailed monitoring of the changes in the distributions of exotic species along elevational gradients will be needed.