Delineating Species Ranges
Distributional limits are a necessary ingredient of the vertebrate modeling process, because they allow us to place bounds on where a species is predicted to occur. We define range, here, as the total areal extent occupied by a given taxon.
The initial overlay of published maps has already been performed by NatureServe (Arlington, Virginia) for mammals, birds, and amphibians. These maps are publicly available (http://www.natureserve.org/getData/animalData.jsp) and are regularly reviewed and updated by Heritage Program biologists. We downloaded all available NatureServe range maps for target species to be mapped and georeferenced them in a common projection (AK Albers). NatureServe range maps were not available for many of the subspecies. Range maps for this group were digitized based on literature descriptions or other available data sources. Polygon range maps were then overlain with watershed units (8-digit HUC’s). The intersection of the HUC and the polygon range map was used to produce a watershed-scale range map.
Usage in Modeling
Species ranges will be used as model delimiters in predicted distribution models.
Watershed-scale range maps, although more coarse scale than the original polygon range maps, provide a standardized unit with which to conduct species richness analyses.