Extralimital Terrestrials: A reassessment of range limits in Alaska's land mammals

Understanding and mitigating the effects of anthropogenic climate change and development on species requires the ability to track distributional changes over time. This is particularly true for species occupying high-latitude regions, which are experiencing a greater magnitude of climate change than the rest of the world. In North America, ranges of many mammals reach their northernmost extent in Alaska, positioning this region at the leading edge of climate-induced distribution change. Over a decade has elapsed since the publication of the last spatial assessments of terrestrial mammals in the state. We compared public occurrence records against commonly referenced range maps to evaluate potential extralimital records and develop repeatable baseline range maps. We compared occurrence records from the Global Biodiversity Information Facility for 64 terrestrial mammals native to mainland Alaska against a variety of range estimates (International Union for the Conservation of Nature, Alaska Gap Analysis Project, and the published literature). We mapped extralimital records and calculated proportions of occurrences encompassed by range extents. We also evaluated extralimital records against published species models, highlighted extralimital observations on U.S. Department of Interior lands, and report on two species of bats new to Alaska since 2014. Range comparisons identified 6,848 extralimital records belonging to 39 of 112 (34.8%) Alaskan species. On average, the Alaska Gap Analysis Project encompassed 95.5% of occurrence records and ranges were deemed accurate (> 90.0% correct) for 31 of 37 species, but overestimated extents for 13 species. International Union for Conservation of Nature range maps encompassed 68.1% of occurrence records and were > 90% accurate for 17 of 39 species. Results are either the product of improved sampling and digitization or represent actual geographic range expansions. Here we provide new data-driven range maps, update standards for the archival of museum-quality locational records and offer recommendations for mapping range changes for monitoring and conservation.