Illinois Natural History Survey - University of Illinois

Mapping the Diversity of Amphibians and Rep tiles in Illinois

Because Illinois is at the crossroads of several different biogeographic realms, it possesses a rich diversity of amphibians and reptiles. The Illinois Natural History Survey (INHS) and the Museum of Natural History (MNH) at the University of Illinois have an extensive repres entation of this diversity in their scientific collections. There are approximately 11,000 preserved specimens, collected from 1842 to the present, in these two collections. These collections are invaluable because they allow us to track individual species and overall species diversity through time and across a landscape that has been dramatically changed by agriculture. To mainta in and potentially enhance this diversity, it is important to know where each species exists and its habitat requirements. 

One of the goals of the National Gap Analysis ( GAP) program is to identify gaps in the representation of the nation's biodiversity. Using geographic information system (GIS) technology, we can use digital maps to identify individual species, species-rich areas, and vegetation types that are unrepresented or underrepresented in existing protected areas. Specifically, the GAP program in Illinois involves vegetation mapping, identifying land stewardship management, and mapping distributions of mammals, birds, amphibians, and reptiles. Currently, we are concentrating our efforts on mapping the locations of Illinois specimens in the INHS and MNH amphibian and reptile collections.

Our approach involves identifying a location for each specimen based on information collected with the specimen. Each specimen may have a "common" location description (e.g., 2 miles east of Champaign) or a legal description (e.g., section 6 of township 34 north, range 5 east), or a town name (e.g., Bement). Using our GIS and computerized U.S. Geological Survey quad maps called digital raster graphics (DRG), we are able to locate roads, streams, and other landmarks used in the location description to determine the collection site. We also have a computerized map of the township, range, and section information for the entire state.

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Western chorus frog, Pseud-acris triseriata.

Using GIS, we can overlay this map layer onto the DRGs to determine the collection site from the legal description. When only a town name is available as the collection site, we use our GIS to match the location of the town hall in our computerized database of town names with the town name in the collection database. Using these various methods and employing GIS technology enables us to build a map of collection sites for all the amphibian and reptile specimens. Additionally, we assign an accuracy code that reflects how sure we are of our location assignment for each specimen.

Each specimen collection site falls within a 63 5-km2 hexagon, which is the mapping unit used by the GAP program. Hexagons were chosen over counties because they are equally sized and easily connect to adjacent states. It is within these hexagons that we determined species richness for amphibians and reptiles.

To build a species richness map, which is the first step in identifying areas of high species diversity, we use GIS and overlay the collection sites onto the GAP hexagons. To determine species richness, we sum up the number of different species that occur in each hexagon. From the species richness map we can identify species as well as groups of species that are not represented in the current network of management areas.

Species richness maps based on preserved specimens in natural history collections can misrepresent species diversity because not all areas of the state were visited with equal frequency by collectors. We know, for example, that collection locations are often clustered around large cities, universities, or outstanding natural features. Some hexagons in the species richness map may have never been visited by collectors. In addition, there are problems with the scale at which the data are displayed. The hexagons cover a large area, which may not adequately represent the diversity of a small pond in someone's backyard.

It is important to be aware of these limitations; however, the ability to map the species richness of amphibians and reptiles for the entire state is a big accomplishment. Our next step will be to use our vegetation mapping and management practices on public lands to identify areas throughout the state that need better management to preserve the biodiversity of amphibians and reptiles in Illinois.

Jocelyn Aycrigg, Center for Wildlife Ecology; Chris Phillips, Center for Biodiversity; Tim Maples, Center for Wildlife Ecology; and Tom Kompare, Center for Biodiversity

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Illinois Natural History Survey

1816 South Oak Street, MC 652
Champaign, IL 61820
217-333-6880
cms@inhs.illinois.edu

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