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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. 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 gap analysis of species protection status).

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 CONUS Data Set

Species List

We created our species lists for the conterminous 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).

Known Range Maps

GAP species range data are coarse representations of the total areal extent a species occupies, in other words, the geographic limits within which a species can be found (Morrison and Hall 2002). These data provide the geographic extent within which we delineate areas of suitable habitat for terrestrial vertebrate species in their species’ habitat maps. The range maps are created by attributing a vector file derived from the 12-digit Hydrologic Unit Dataset (USDA NRCS 2009). Modifications to that dataset are described here. Attribution of the season range for each species was based on the literature and online sources (See Cross Reference section of the metadata). Attribution for each hydrologic unit within the range included values for occurrence (extant, possibly present, potentially present, extirpated), season (year-round, summer, winter, migratory, vagrant), origin (native, introduced, reintroduced, vagrant), and reproductive use (breeding, non-breeding, both). These species range data provide the biological context within which to build our species distribution models.

Predicted Habitat Maps

Gap Analysis Project (GAP) habitat maps are predictions of the spatial distribution of suitable environmental and land cover conditions within the United States for individual species. Mapped areas represent places where the environment is suitable for the species to occur (i.e. suitable to support one or more life history requirements for breeding, resting, or foraging), while areas not included in the map are those predicted to be unsuitable for the species. While the actual distributions of many species are likely to be habitat limited, suitable habitat will not always be occupied because of population dynamics and species interactions. Furthermore, these maps correspond to midscale characterizations of landscapes, but individual animals may deem areas to be unsuitable because of presence or absence of fine-scale features and characteristics that are not represented in our models (e.g. snags, vernal pools, shrubby undergrowth). These maps are intended to be used at a 1:100,000 or smaller map scale.

These habitat maps are created by applying a deductive habitat model to remotely-sensed data layers within a species’ range. The deductive habitat models are built by compiling information on species’ habitat associations into a relational database. Information is compiled from the best available characterizations of species’ habitat, which included species accounts in books and databases, as well as primary peer-reviewed literature. The literature references for each species are included in the “Species Habitat Model Report” and “Machine Readable Habitat Database Parameters” files attached to each habitat map item in the ScienceBase repository. For all species, the compiled habitat information is used by a biologist to determine which of the ecological systems and land use classes represented in the National Gap Analysis Project’s (GAP) Land Cover Map Ver. 1.0 that species is associated with. The name of the biologist who conducted the literature review and assembled the modeling parameters is shown as the “editor” type contact for each habitat map item in the repository.

For many species, information on other mapped factors that define the environment that is suitable is also entered into the database. These factors included elevation (i.e. minimum, maximum), proximity to water features, proximity to wetlands, level of human development, forest ecotone width, and forest edge; and each of these factors corresponded to a data layer that is available during the map production. The individual datasets used in the modeling process with these parameters are also made available in the ScienceBase repository. The “Machine Readable Habitat Database Parameters” JSON file attached to each species habitat map item has an “input_layers” object that contains the specific parameter names and references (via Digital Object Identifier) to the input data used with that parameter. The specific parameters for each species were output from the database used in the modeling and mapping process to the “Species Habitat Model Report” and “Machine Readable Habitat Database Parameters” files attached to each habitat map item in the repository.

Additional Data

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

Other Datasets

GAP maintains other data of interest, including legacy datasets from previous regional and state projects.
Other Data >>

Citations

Known Range Maps
U.S. Geological Survey – Gap Analysis Project, 2018, U.S.Geological Survey – Gap Analysis Project Species Range Maps CONUS_2001: U.S. Geological Survey data release, https://doi.org/10.5066/F7Q81B3R

Predicted Habitat Maps
U.S. Geological Survey – Gap Analysis Project, 2018, U.S. Geological Survey – Gap Analysis Project Species Habitat Maps CONUS_2001: U.S. Geological Survey data release, https://doi.org/10.5066/F7V122T2

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.

CONTACTS for Species Data >>

 

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