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Species Data and Modeling

GAP is delineating species range and predicted distribution maps for more than 2,000 species that occur within the continental US as well as Alaska, Hawaii, Puerto Rico, and the U.S. Virgin Islands (we will make these maps and datasets available as they are completed). Our goal is to build species range maps and distribution models with the best available data for assessing conservation status, conservation planning, and research (e.g., climate change impacts).

Why are these Data Important?

Knowledge of a species geographic and ecological location is fundamental to many aspects of biodiversity conservation and for understanding spatial patterns of species occurrences. Furthermore, they will provide the basis of a national biodiversity assessment (e.g., species richness, historical vs. current).

How National GAP Species Data are being used

  • To enhance understanding of spatial patterns of species occurrence (e.g., species richness)
  • As a core data input to a national biodiversity assessment of vertebrate species occurring in United States
  • To provide information about the location of a species to enhance understanding of how that species will adapt to the effects of climate change.
  • As core datasets from which new iterations of the maps and models can be developed as additional data become available.

Description of the Data

We created our species lists for the U.S. by initially compiling species lists from our regional projects in the Southwest (SWReGAP), Southeast (SEGAP), and Northwest (NWGAP). We then filled in areas not represented by these regional projects with species lists from all the remaining states (e.g., California, Midwestern and Northeastern states). Once a comprehensive list was compiled, each species’ taxonomic classification was verified using the most current information available (Banks et al. 2008, Crother 2008, Wilson and Reeder 2005).

Citation

Range Maps
U.S. Geological Survey Gap Analysis Program. 2011. National GAP vertebrate species range data. http://gapanalysis.usgs.gov/species

Distribution models
U.S. Geological Survey Gap Analysis Program. 2011. National GAP vertebrate species distribution model. http://gapanalysis.usgs.gov/species

For citation information for additional GAP species modeling data, see our metadata.

Description – Range Maps

We defined a species range as a coarse representation of the total areal extent of a species or the geographic limits within which a species can be found (Morrison and Hall 2002). To represent these geographic limits, we used a national database of standardized 12-digit hydrological units (HUCs; U.S. Geological Survey and U.S. Department of Agriculture, Natural Resources Conservation service 2009). Ranges maps were compiled and attributed with information from SWReGAP, SEGAP, NatureServe, and IUCN. Each range map contains information regarding occurrence/presence, origin, reproductive use, and seasonal use.

Description – Distribution Models

We defined a species distribution as the spatial arrangement of environments suitable for occupation by a species. In other words, a species distribution is created using a deductive model to predict areas suitable for occupation within a species range. Currently, we are focusing our efforts on building, expanding, or updating our deductive species models, but we will also expand our inductive modeling efforts over time. For species entirely within one of our regional projects, we are using existing distribution models created by those respective efforts as our national distribution model.

Get current status of species range and distribution models (163 kb, csv file)

Additional Data

Several key national ancillary data layers have been created as model inputs for our national modeling effort and are available for download:

Data Limitations

It should be noted that all our ranges and distribution models are predictions about the occurrence of a species within the U.S. GAP ranges and distribution models are intended for use at the landscape scale (i.e., areas the size of square kilometers). They are not intended to be precise predictions of species occurrence/absence at local scales (areas the size of square meters). It is important for GAP data users to evaluate the suitability of the data for their intended purpose.

GAP aims to use the best available information to create species ranges and distribution models. GAP relies on existing data and expert opinions from partners and collaborators (e.g., State Natural Heritage Programs).

Species range maps and distribution models are viewed as single iteration based on best available information. We encourage biologists and data users to assess GAP’s species ranges and distribution models, and give us feedback so that we can continually improve our models and ultimately our ability to conserve biodiversity.

All of GAP’s ranges and distribution models have been reviewed by experts and compared to other data sources for accuracy. The accuracy of the species ranges and distribution models varies from species to species in part because habitat preferences and behaviors vary seasonally and annually (Edwards et al. 1996). However, those species for which thorough knowledge of habitat preferences exists are better represented than those for which little is known (i.e., rare or small populations) or vary widely both spatially and temporally. Species with highly restrictive distributions are very difficult to model accurately because their habitat cannot be predicted within the 30 m resolution of our land cover data and distribution maps. We accept the uncertainty within some ranges and distribution models because we believe these data provide basic information and serve an important purpose by highlighting where more data are needed.

Despite these limitations, we believe GAP species ranges and distribution models are valuable and relevant for addressing broad landscape level conservation questions and research.

References

Banks, R. C., R. T. Chesser, C. Cicero, J. L. Dunn, A. W. Kratter, I. J. Lovette, P. C. Rasmussen, J. V. Remsen, Jr., J. D. Rising, D. F. Stotz, and K. Winker. 2008. Forty-ninth supplement to the American Ornithologists’ Union Check-list of North American Birds. The Auk 125:758-768. Available from: www.aou.org/checklist/suppl/AOU_checklist_suppl_49.pdf.

Crother, B. I. 2008. Scientific and standard English names of amphibians and reptiles of North America north of Mexico, with comments regarding confidence in our understanding. 6th edition. Herpetological Circular No. 37, Society for the Study of Amphibians and Reptiles. Available from: www.ssarherps.org/pages/comm_names/Index.php

Morrison, M. L., and L. S. Hall. 2002. Standard terminology: Toward a common language to advance ecological understanding and application. Pages 43-52 in Predicting Species Occurrences: Issues of accuracy and scale. Editors: J. M. Scott, P. J. Heglund, and M. L. Morrison, et al., Island Press.

U.S. Geological Survey and U.S. Department of Agriculture, Natural Resources Conservation Service, 2009, Federal guidelines, requirements, and procedures for the national Watershed Boundary Dataset: U.S. Geological Survey Techniques and Methods 11:3, 55 p. Available from: www.ncgc.nrcs.usda.gov/products/datasets/watershed/

Wilson, D. E., and D. M. Reeder. 2005. Mammal Species of the World. A Taxonomic and Geographic Reference, 3rd edition. Johns Hopkins University Press. Available from: www.bucknell/edu/msw3.

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