Characterizing habitat relationships and establishing monitoring strategies for an alpine obligate

Abstract

Alpine species have evolved to live in some of the harshest and most climatically diverse areas in the world, yet changes in climate are rapidly altering the areas alpine obligates call home. Warming temperatures are marching species to higher elevations and towards the poles, especially threatening species at the southern extent of their distributions. Understanding habitat requirements and monitoring abundance of species like the hoary marmot (Marmota caligata) at their southern extent will be crucial for tracking the magnitude of change that has begun in alpine ecosystems. We conducted double-observer occupancy surveys to collect presence-absence data and assess habitat characteristics important for the occurrence of hoary marmots; survey sites were within 5 mountain ranges in western Montana, the southern edge of this species' distribution. Marmots preferred shallow slopes, southern aspects, and areas with shrubs present. These preferences suggest that hoary marmots select habitat based on limitations they experience during both winter and summer, but winter conditions may play a stronger role in habitat selection. We then used our occupancy data to assess a broad suite of landscape variables at multiple spatial scales to create a predictive map of hoary marmot habitat throughout their distribution in Montana. We employed our predictive map to conduct a spatially-explicit power analysis and assess the ability of different monitoring strategies to detect a negative trend in abundance of marmot colonies. We were able to detect a 50% decline in colony abundance over 30 years by surveying 7-87% of sites > or = 4 times every 3 years. We found that we were more likely to detect a negative trend when the abundance of colonies was higher. Based on this information, we suggest that if management objectives include assessing population trend from occupancy, monitoring plans should be implemented sooner rather than later. Habitat associations and population status information are lacking for many species. Our study has provided a way to collect valuable information to monitor and manage an alpine species. The methods we have used can be applied to monitor other species that are hard to access and our results provide information for conserving alpine species over their distribution.