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Central to the concept of Gap Analysis is the development of species distribution maps through the use of models. In Oregon, the most recent maps have been compiled into the second edition of the Atlas of Oregon Wildlife (OSU Press). The models are developed using the assumption that most wildlife species use preferred habitats within their known range of distribution. When we select the appropriate habitats occurring in an area in which the species have been observed, we can predict that the species may be there without having to survey the entire area. OR-GAP has prepared species distributions based on the current habitats of Oregon, as well as the presettlement habitats.
OR-GAP has created maps of 474 native and introduced terrestrial vertebrate species occurring across the state of Oregon. Every wildlife species is mapped as occurring in EMAP hexagons, watersheds, and Oregon counties. For the hexagon distribution, species are recorded as documented (>95% confidence), probable (80-95% confidence) and possible (20-80% confidence). For the GAP models, we use only hexagons with probable and documented occurrences.
The 2004 maps can be downloaded as an ArcGIS 9.1 geodatabase. These maps were not as carefully peer reviewed as the 1999 GAP maps, but they are at much a higher resolution. We would appreciate any comments or corrections. Available online: (zip file 44 MB).
Oregon Natural Heritage Program regularly works with partners such as Metro to refine these models for application at a localized planning scale. These new models not only let us predict whether a species is likely to occur, but help us decide whether an area provides good habitat for the species based upon the quality of the surrounding landscape and the suitability of the vegetation.
An map of the existing (top) and historic (bottom) distribution of the pronghorn antelope is shown below.
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