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283 In a little over a century, the prairie pothole region of the northern Great Plains has been transformed from a contiguous expanse of wetlands and grasslands into a highly fragmented agricultural landscape. Regional wetland losses due to agricultural activities and urbanization have been extensive and widespread , exceeding 90% in northwestern Iowa and western Minnesota (Tiner, 1984; Dahl, 1990; Leja, 1998). Declines in amphibian numbers coinciding with the habitat loss have heightened concerns over the future of amphibian populations (e.g., Barinaga, 1990; Blaustein and Wake, 1990, 1995; Wake, 1991; Lannoo, 1998b). South Dakota (199,500 km2 in area), a state that lies in the prairie pothole region, is bisected into two nearly equal eastern and western segments by the upper Missouri River. The eastern portion is a poorly drained, glaciated landscape with an abundance of wetlands covering approximately 10% of the total land area (Johnson and Higgins, 1997). In contrast, the western portion is a well-drained, non-glaciated landscape composed of ancient sediments. Despite a 45% decline in wetland numbers in eastern South Dakota, more than 930,000 wetland basins remain (Johnson and Higgins, 1997). While concern about amphibian declines have produced conservation initiatives in other Midwestern states (Lannoo, 1998b), in South Dakota such programs have not been implemented and there remains a lack of basic knowledge concerning the distribution and habitat use of South Dakota frogs, toads, and salamanders (Fischer, 1998; Fischer et al., 1999). To address this lack of data on South Dakota anurans, we present distribution maps for 12 frog and toad species. These maps include new records from fieldwork conducted in 1997–98, where we surveyed 1,496 wetland sites throughout all 44 counties in eastern South Dakota (Fischer, 1998). Because no one had conducted extensive survey work in western South Dakota, we construct distribution maps using historical data from the South Dakota Natural Heritage Database. We also assess how breeding anurans use habitats throughout eastern South Dakota by using occurrence rates of 11 species in seven different wetland types. Finally, to assist future monitoring programs, we follow Mossman et al. (1998) in using field data to recommend ranges of dates for sampling each species. Methods We conducted anuran auditory surveys throughout eastern South Dakota. In 1997, we selected 14 transects by partitioning eastern South Dakota into 13 km-wide strata. Within each stratum, we randomly selected one Public Land Survey section line as a transect origin. We then established transects on east-west roads closest to the latitude of origin; transects were separated by at least 3.2 km. We eliminated major roadways (e.g., Interstate 90) from transect selection to reduce auditory disturbances. In 1998, we positioned eight new transects along latitudes bisecting counties in which few anurans were recorded during the 1997 surveys. To supplement these transect surveys, we conducted auditory surveys at wetlands along every available stretch of roadway in areas where historical records have indicated the presence of isolated anuran populations. We overlaid transects onto a wetland geographic information system developed for eastern South Dakota (Johnson and Higgins, 1997). We classified wetlands according to Stewart and Kantrud (1971) into seven classes: temporary, seasonal , semipermanent, permanent, manmade (e.g., stock dams), undifferentiated tillage ponds, and riverine. We randomly selected roadside wetlands to survey sites that were within 100 m of the transect line. In counties with high wetland densities ( 75 wetlands/km2 ), we surveyed at least three wetlands in each class along each transect. In counties with low wetland densities, we surveyed all wetlands within 100 m of the transect. We followed an established protocol that has been extensively used to monitor anurans in the Midwest (Hemesath , 1998; Johnson, 1998b; Mossman et al., 1998). We surveyed wetlands in the spring when water temperatures reached 10 C (Johnson and Batie, 1996; Mossman et al., 1998). We conducted surveys from 22 April–19 May and 2 June–30 June in 1997, and from 25 April–28 May and 28 May–29 June in 1998. We began surveys in the south and proceeded northward to account for latitudinal differences in breeding phenology. We recorded male mating calls during three-minute survey periods at each wetland (after Zimmerman, 1994; Shirose FO RTY-O N E Distribution of South Dakota Anurans DAVID E. NAUGLE, TATE D. FISCHER, KENNETH F. HIGGINS, AND DOUGLAS C. BACKLUND et al., 1995; see also Mossman et al., 1998). We identified calling anurans to species and assigned the relative abundance of each species to one of the following classes: 1  individuals...

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