Evan M. Rehm

Rates of upslope shifts for tropical species depend on life history and dispersal mode.

The recent paper by Freeman and Class Freeman (1) adds to a growing body of literature documenting the upslope distributional shifts of tropical montane species in response to climate change. Armed with just a handful of studies from the tropics, the authors compare upslope shift rates between tropical and nontropical species and conclude that tropical species are, on average, shifting their distributions faster than temperate species. On the basis of this broad comparison, the authors contend that tropical montane species are more sensitive to temperature changes than are temperate species. Although this is a laudable first attempt to synthesize basic patterns of range shifts in tropical species, I believe that the authors drew spurious conclusions because they overlooked some basic ecological differences between taxa.

Downward shift of montane grasslands exemplifies the dual threat of human disturbances to cloud forest biodiversity

The study by Morueta-Holme et al. (1) provides unique and invaluable insight into how tropical montane ecosystems have responded to climate change and other anthropogenic disturbances over the past two-plus centuries. Clearly, one of the most important findings of their study is that many species and ecosystems have shifted their distributions upslope to higher elevations, in accord with rising global mean temperatures (1). Another extremely important finding of the study that is deserving of extra attention is that the high-elevation grasslands of Chimborazo (i.e., the Pajonal) have expanded their distributions not only upslope but also downslope by several hundreds of meters. The upslope …