Distribution changes in páramo plants from the equatorial high Andes in response to increasing temperature and humidity variation since 1880

Climatic changes threaten the diverse and highly endemic páramo flora of the equatorial Andes with species loss and reduction of plant community diversity. Edward Whymper’s findings in his botanical exploration of the Ecuadorian Andes in 1880 offer an opportunity to examine the impact of climate changes on species distribution over time. To achieve these goals, we revised Whymper’s historical plant species collections, recorded elevational distribution of the same species along his 1880 sampling routes on two volcanoes, Chimborazo and Antisana, and applied to them ecological indicator values. Of the species recorded by Whymper, 24 on Antisana and 21 on Chimborazo, we resampled 21 and 14 of those species, respectively, in 2020. The highest record we found on Chimborazo was at 5385 m, seven meters above the zero-richness elevation predicted from Whymper’s distribution data, and at 4937 m on Antisana, 113 m below it. Mean upper range limits of species have shifted upward by 91.7 m on Chimborazo and by 27.1 m on Antisana, suggesting mean shift rates of 6.6 m and 1.9 m per decade, respectively. This rate of upslope migration ranks among the slowest reported worldwide. Humidity ecological indicator values suggest that species composition of páramo plant communities changed since 1880 in response not only to rising temperature, but also increasing dryness. Rather than a uniform upslope migration, the response of páramo plants to climate changes in the equatorial Andes has been species-specific, likely driven, among other factors, by coupled effects of increasing temperature and declining humidity.