Abstract
North America’s coastal mountains are particularly vulnerable to climate change, yet harbour a number of endemic species. With little room “at the top” to track shifting climate envelopes, alpine species may be especially negatively affected by climate-induced habitat fragmentation. We ask how climate change will affect the total amount, mean patch size, and number of patches of suitable habitat for Vancouver Island White-tailed Ptarmigan (Lagopus leucura saxatilis; VIWTP), a threatened, endemic alpine bird. Using a Random Forest model and a unique dataset consisting of citizen science observations combined with field surveys, we predict the distribution and configuration of potential suitable summer habitat for VIWTP under baseline and future (2020s, 2050s, and 2080s) climates using three general circulation models and two greenhouse gas scenarios. VIWTP summer habitat is predicted to decline by an average of 25%, 44%, and 56% by the 2020s, 2050s, and 2080s, respectively, under the low greenhouse gas scenario and 27%, 59%, and 74% under the high scenario. Habitat patches are predicted to become fragmented, with a 52–79% reduction in mean patch size. The average elevation of suitable habitat patches is expected to increase, reflecting a loss of patches at lower elevations. Thus ptarmigan are in danger of being “squeezed off the mountain”, as their remaining suitable habitat will be increasingly confined to mountaintops in the center of the island. The extent to which ptarmigan will be able to persist in increasingly fragmented habitat is unclear. Much will depend on their ability to move throughout a more heterogeneous landscape, utilize smaller breeding areas, and survive increasingly variable climate extremes. Our results emphasize the importance of continued monitoring and protection for high elevation specialist species, and suggest that White-tailed Ptarmigan should be considered an indicator species for alpine ecosystems in the face of climate change.
Highlights
Climate-related range shifts are discernable across the globe for many animal species [1] and clear fingerprints related to climate change are detectable on bird species assemblages [2,3]
In a previous study describing the quantity and location of suitable ptarmigan breeding habitat on Vancouver Island, we showed that species distribution models trained using opportunistic observations submitted by hikers are comparable in quality and predictions to models trained using time- and cost-intensive field survey data [36]
Precipitation as snow, aspect, and mean summer precipitation all were of intermediate importance, while slope, vector ruggedness measure (VRM), and compound topographic index (CTI) were of low importance
Summary
Climate-related range shifts are discernable across the globe for many animal species [1] and clear fingerprints related to climate change are detectable on bird species assemblages [2,3]. Mountain ecosystems are among the most at risk from climate change [4]. Mountains often have high levels of biodiversity and harbour large numbers of endemic species [5,6], many of which are restricted to alpine habitats [7]. Such habitats are gradually being lost due to tree and shrub encroachment [8,9], resulting in range contractions of alpine species at their lower altitudinal limits [10,11]. Increased competition from invasive species and low elevation generalists may further accelerate population declines for alpine specialist species under a warming climate [15,16]
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