Projecting the future of an alpine ungulate under climate change scenarios

Abstract

Climate change represents a primary threat to species persistence and biodiversity at a global scale. Cold adapted alpine species are especially sensitive to climate change and can offer key "early warning signs" about deleterious effects of predicted change. Among mountain ungulates, survival, a key determinant of demographic performance, may be influenced by future climate in complex, and possibly opposing ways. Demographic data collected from 447 mountain goats in 10 coastal Alaska, USA, populations over a 37-year time span indicated that survival is highest during low snowfall winters and cool summers. However, general circulation models (GCMs) predict future increase in summer temperature and decline in winter snowfall. To disentangle how these opposing climate-driven effects influence mountain goat populations, we developed an age-structured population model to project mountain goat population trajectories for 10 different GCM/emissions scenarios relevant for coastal Alaska. Projected increases in summer temperature had stronger negative effects on population trajectories than the positive demographic effects of reduced winter snowfall. In 5 of the 10 GCM/representative concentration pathway (RCP) scenarios, the net effect of projected climate change was extinction over a 70-year time window (2015-2085); smaller initial populations were more likely to go extinct faster than larger populations. Using a resource selection modeling approach, we determined that distributional shifts to higher elevation (i.e., "thermoneutral") summer range was unlikely to be a viable behavioral adaptation strategy; due to the conical shape of mountains, summer range was expected to decline by 17%-86% for 7 of the 10 GCM/RCP scenarios. Projected declines of mountain goat populations are driven by climate-linked bottom-up mechanisms and may have wide ranging implications for alpine ecosystems. These analyses elucidate how projected climate change can negatively alter population dynamics of a sentinel alpine species and provide insight into how demographic modeling can be used to assess risk to species persistence.

Delayed spring onset drives declines in abundance and recruitment in a mountain ungulate

“…Similarly, growing season conditions have been implicated as important factors in the population dynamics of mountain goats (White et al. , ) and bighorn sheep (Portier et al. , Pettorelli et al.…”

“…Understanding the role of primary productivity in mitigating the effects of extreme weather events is important because long‐term climate impacts are expected to reduce the amount of available habitat to mountain ungulates (White et al. ).…”

“…In addition, primary productivity is directly related to weather conditions and has been identified as a driver of abundance in some smaller herbivores in the subarctic . Similarly, growing season conditions have been implicated as important factors in the population dynamics of mountain goats (White et al 2011(White et al , 2018 and bighorn sheep (Portier et al 1998, Pettorelli et al 2007, and affect horn growth in Alpine ibex (Buntgen et al 2014) and Dall's sheep (Loehr et al 2010). In the context of past work, the spatial variation in the response that we observed suggests that increased primary productivity at lower latitudes may buffer the effects of spring conditions on population dynamics.…”

“…For example, while the Nabesna subarea did not exhibit declines in adults (i.e., reduced adult survival), the basic pattern of reduced lamb-to-ewe-like sheep ratios during later springs was observed. Understanding the role of primary productivity in mitigating the effects of extreme weather events is important because long-term climate impacts are expected to reduce the amount of available habitat to mountain ungulates (White et al 2018).…”

Climatically driven changes in primary production propagate through trophic levels

“…As expansion and intensification of human land use fragments natural habitats (Haddad et al, ; Theobald, Travis, Drummond, & Gordon, ), coupled climate‐vegetation models predict lower and more variable productivity in arid and semiarid regions worldwide (Garfin, Jardine, Merideth, Black, & LeRoy, ; Seager et al, ). Although confidence is high that climate change will threaten rare species with narrow habitat requirements or small geographic ranges (Laidre et al, ; Stewart et al, ; White, Gregovich, & Levi, ), comparatively little is known about how these changes will affect the abundance of widely distributed species with broad environmental tolerances, or how these effects will transfer through food chains.…”