Alan Yanahan Abstracts

Alan Yanahan

Ph.D. Candidate

Entomology & Insect Sciences GIDP

The 9th Biennial Conference of the International Biogeography Society

Malaga, Spain

January 8-12, 2019

The Madrean Sky Island Archipelago is a North American biodiversity hotspot comprised of ~60 isolated mountains that span the Cordilleran Gap between the Rocky Mountains and the Sierra Madre Occidental. Characterized by discrete patches of high-elevation montane habitat, these ‘sky islands’ serve as stepping stones across a ‘sea’ of desert scrub/grassland. Over this coming century, the region is expected to shift towards a warmer and drier climate. We used climate envelope modelling to predict how the spatial distribution of montane habitat will be affected by climate change. To approximate the current distribution of montane habitat, we built climate envelope models for five high-elevation species (Ceanothus fendleri, Pinus strobiformis, Quercus gambelii, Sciurus aberti, Synuchus dubius). The resulting models were projected under multiple climate change scenarios—four greenhouse gas concentration trajectories (RCP 2.6, 4.5, 6.0, 8.5) for each of three climate models (CCSM4, MPI-ESM-LR, NorESM1-M)—to generate predicted distributions for the years 2050 and 2070. While the climate models differ with respect to their predictions as to whether effects of future climate change will be mild (CCSM4), moderate (MPI-ESM-LR), or severe (NorESM1-M), they all agree that by as early as year 2050, under even the most conservative greenhouse gas concentration trajectory (RCP 2.6), there will be significant montane habitat loss and increased patch isolation. Our results suggest that under 21st century climate change, the Madrean Sky Islands will become increasingly isolated due to montane habitat loss. This may affect their ability to serve as stepping stones and have negative implications for the region’s biodiversity.

Abstract for Lay Audience

The Madrean Sky Island Archipelago is a biodiversity hotspot located within the southwestern United States and northwestern Mexico. The region is characterized by the over 60 isolated mountains that span the Cordilleran Gap between the Colorado Plateau/Rocky Mountains to the north and the Sierra Madre Occidental to the south. These isolated mountains are called "Sky Islands" because they contain discrete patches of high-elevation woodlands surrounded by a “sea” of desert and/or grassland. The high-elevation woodlands are especially susceptible to 21st century climate change. As temperatures in the region rise, the woodlands are expected to retreat up the mountains to escape the heat. But the woodlands cannot retreat indefinitely. Eventually, they will reach the mountain tops and there will be nowhere else to go. To determine whether future climate change has the potential to cause the Sky Island woodlands to disappear, we used a technique called climate envelope modelling. This technique allows us to map the climate that is favored by the Sky Island woodlands which will show us all the locations where the woodlands can currently be found. As expected, the woodlands prefer cooler, wetter climates and are found at higher elevations. But what about under future climate change…after the region has become warmer and drier…will the woodlands still be present? When we looked ahead to the year 2050 and mapped all the locations that are expected to remain cool and wet enough for the Sky Island woodlands to survive, we found that all the current locations had shrunk significantly and many of them had disappeared. This suggests that we will lose many of our Sky Island woodlands to 21st century climate change. Because the Sky Island woodlands are home to many species, woodland loss can potentially impact entire communities and ultimately lead to a devastating decline in biodiversity for the Madrean Sky Island Archipelago.