Its biota has evolved in the arid rain shadow of the Rocky Mountains, average annual precipitation ranging from approximately 10 inches in the foothills of Colorado to 50 inches in eastern Kansas.  Rainfall levels determine the predominant historical grassland types, with shortgrass prairie furthest west, mixed-grass prairie through the center, and tallgrass prairie on the eastern edge (Bryce et al. 1996, Chapman et al. 2001).

The four states included in the present survey, Kansas, Nebraska, South Dakota, and North Dakota, lie primarily in the drainage of the Missouri River, with its major tributaries, the Kansas/Republican, the Platte, the James, the Niobrara, and the Cheyenne.  Southern Kansas drains south into the Arkansas River with its major tributaries the Cimarron and the Neosho, and northern North Dakota drains north into the Red River, with its tributaries the Sheyenne and the Souris/Assiniboine.  See Figure 1 below.

Our study area also encompasses many dense regions of small wetlands and ponds. These include the Sandhill Lakes and Rainwater Basins of Nebraska, the wetland pools of the McPherson Valley in Kansas, and the extensive prairie pothole region of eastern North Dakota and northeastern South Dakota (USGS 1996). The southern edge of the prairie potholes is approximately the extent of the most recent glacial maximum, the Wisconsian (Wayne 1985). The reduction in the number and area of wetlands in this region is a historical trend, primarily due to the encroachment of agriculture (USGS 1996). Prairie pothole wetlands declined by over 60% from 1850 to 1980 and continue to be reduced by about 1% yearly (Dahl 2014).

Figure 1.  The drainage systems of our four-state Great Plains study area, showing sample sites.

The Great Plains Ecoregion is not famous for its aquatic biodiversity.  When Lewis and Clark sailed up the Missouri River in 1804, they enthused about the vastness of the prairie, the richness of the ungulate fauna, and the diversity of the Native American cultures they met on their journey.  The freshwater gastropod fauna garnered nary a mention.

Nor indeed did aquatic biodiversity figure in the first wave of European Americans who followed Lewis and Clark into the Great Plains and beyond, just passing through.  The town of Kansas, now Kansas City, was formed in 1838 as an important starting point for the Oregon and Santa Fe trails.  Omaha, Nebraska, was founded as Omaha City in 1854 and became the starting point for the first transcontinental railroad line, completed in 1869 (Berg, 2011).

With the railroads came a second wave of European American settlement, which with the passage of the Homestead Act in 1862 and the cessation of hostilities in 1865, became a deluge (Wishart 2013).  Thousands of migrant families began to arrive carrying the agricultural methods of eastern U.S. settlements, livestock, and crops to feed them, primarily corn (Hudson, 2011).  The rapid expansion of farm culture throughout the Great Plains in the late nineteenth century, together with the cyclic droughts and the economic hardships that followed, have been well-documented (Wishart 2011).

Today the Great Plains of North America are an agricultural-dominated landscape, crops dependent upon rainfall and growing season (Hudson 2011).  Wheat is the primary crop in the northern and drier parts of our four-state study area, in the Dakotas and the western halves of Nebraska and Kansas.  Corn, primarily for livestock feed, dominates eastern Nebraska and Kansas.  The Nebraska Sand Hills are primarily given over to livestock grazing.

Kansas - Of the four states covered in the present survey, the freshwater gastropod fauna of The Jayhawker State is best known.  The first surveys of freshwater gastropods in Kansas were completed as a part of the Washburn Biologic Survey and published by R. Ellsworth Call (1885a, 1885b, 1886, 1887).  Call listed collection localities for 25 species, although several have been synonymized in modern times.  Based on the locations observed, six species appeared common, Helisoma trivolvis, Helisoma anceps, Physa gyrina, Physa acuta, Campeloma decisum, and Lymnaea catascopium.

Hanna (1909) provided range expansions for several of Call’s species, although adding no new species to his list. He documented seventeen species from Douglas County, in the vicinity of Lawrence, remarking as he did that ancylids were absent from his survey. That same year, Baker (1909) reported fresh records of four freshwater gastropods from Kansas, including Lymnaea humilis (listed as L. obrussa) new to the state.

Dorothea Franzen and A. Byron Leonard contributed a list of eight species from Kingman County in the south-central part of the state in 1942.  Subsequent work added range expansions for nine mollusks and included the first observations of Pleurocera potosienis and P. acuta for the Jayhawker State (Franzen 1944).

Leonard’s (1959) “Handbook of Gastropods in Kansas” was a landmark contribution to our understanding of the malacofauna of the Great Plains.  Working from collections at the University of Kansas, Leonard documented 20 species of freshwater snails, giving figures, detailed descriptions, range maps, ecological notes, and synonymy.

Since Leonard’s work, Kansas has received some attention, including a study on the habitat preferences of terrestrial and aquatic mollusks, which noted Physa gyrina (listed as Physa hawnii) as the most abundant freshwater gastropod (Basch et al. 1961).  Branson (1963, 1969) updated distribution records and taxonomy, lumping (for example) Physa anatina with Physa virgata.  Angelo and colleagues (2002) published a revision of the distribution of the Kansas prosobranch snails in 2002, suggesting as they did that Amnicola limosa might be extirpated.

Nebraska - The earliest systematic collections of the freshwater gastropod fauna of the Great Plains were made by Ferdinand Hayden in 1868, shortly after Nebraska was granted statehood.  Lists and locations of the freshwater snails collected by the Hayden Expedition were published by Tryon (1868),  Aughey (1877), and Walker (1906). Aughey listed forty-nine species and estimated their rarity, while Tryon (1868) reported five species from the Omaha area. Walker (1906) listed locations for 18 species, expanding the distribution of some species while adding ten species he considered new to the State. These combined records make up the bulk of the species of freshwater gastropods reported historically for The Cornhusker State.

More recent work in Nebraska includes Gugler (1969) and Freeman and Perkins (1992, 1997). Gugler (1969) reported abundant Valvata tricarinata in a western Nebraska lake, although historical sources indicated but a single rare occurrence. Freeman and Perkins (1992, 1997) sampled the Platte and Niobrara Rivers, providing vital river data on seven species.

Stephen (2015) reviewed and evaluated all historical and recent records of freshwater gastropods for the state of Nebraska, updating the taxonomy to modern standards.  Ultimately, he counted 31 valid species documented for the Cornhusker State, 30 indigenous and one non-indigenous.  Based on the number of historical records, the four most common species in Nebraska are Physa gyrina, Physa acuta, Lymnaea elodes, and Aplexa elongata.

South Dakota – Most of the previous research on the freshwater gastropods of the Mount Rushmore State has come from just four studies, those of Over (1915, 1915a, 1928) and Henderson (1927). Over (1915a, 1915b) listed 35 species, each with counties of record, later (1928) adding seven species. Henderson (1927) provided county range extensions for eleven species on Over’s list. 

Recent work on South Dakota freshwater gastropods includes the distribution of the non-indigenous snail Melanoides tuberculata within the U.S., including Fall River and some smaller streams in and around Hot Springs, South Dakota (Anderson 2004). Evaluation of the records, combining synonyms and omitting likely misidentifications, indicate that 25 species were historically present within the State (Stephen 2018). The historically common species (based on the number of literature records) are Physa gyrina, Helisoma trivolvis, Lymnaea elodes, and Lymnnaea caperata.

North Dakota – The freshwater gastropod fauna of North Dakota was very poorly documented for the first 100 years of its statehood.  Hayden (1862) mentioned two species of Amnicola at Fort Berthold along the Missouri River, now under Lake Sakakawea.  Physa gouldii (subsequently synonymized under P. gyrina) was described by Clench (1935) from the Mouse River.

Tuthill and Laird (1963) surveyed the alkaline lakes and palustrine habitats of North Dakota’s Missouri Coteau (hilly upland) region, identifying 11 species, Physa and Gyraulus identified to genus only.  They were impressed by the range of alkalinities tolerated by several of the species, Helisoma trivolvis, Lymnaea elodes and Physa sp. observed at pH ranging from 6.23 to 8.7.

Alan Cvancara began his comprehensive survey of the aquatic mollusks of North Dakota with a (1974) review of the fossil records, following nine years later with a thorough and important guide to the recent fauna.  His (1983) report included descriptions, distribution maps, and ecological notes for twenty-two freshwater snail species, the five most common being Ferrissia rivularis, Gyraulus parvus, Helisoma trivolvis, Physa gyrina, and Physa integra (now Physa acuta).

> Methods

The database analyzed here comprises 1,474 records: 574 collected personally and 900 collected by state natural resource agencies.  Of these 620 came from Kansas, 362 from Nebraska, 314 from South Dakota, and 178 from North Dakota.

Through the 1970s and 1980s, the Kansas Biological Survey conducted a comprehensive survey of the macroinvertebrate fauna inhabiting waters across the state. Methods were entirely qualitative. Sample sites were chosen to cover the full range of freshwater habitat types in the state across all counties and ecoregions, from playas, ditches, and private farm ponds to large rivers and reservoirs. Collections were made by teams of biologists using a variety of tools, kick nets, and simple visual surveys. The freshwater gastropod component of these extensive collections was curated into the Museum of the University of Kansas.

We visited the KU Museum on January 25 – 27, 2022, reviewing 642 freshwater gastropod lots collected from 1971 – 1981 from Kansas. Subtracting unidentifiable and otherwise unqualified lots and expanding mixed lots ultimately yielded 580 records. The remainder of our Kansas records were from personal collections primarily by our collaborator, Will K. Reeves.

BJS collected and compiled most of our Nebraska and South Dakota records in connection with his dissertation research (Stephen 2017, 2018). Additional records for Nebraska and South Dakota were from personal collections by WKR and others. Macrobenthic samples collected from the Rivers and Streams Program of the Nebraska Game and Parks Commission using qualitative visual surveys contributed 142 Nebraska records. All Nebraska and South Dakota samples are in the personal collections of BJS.

We visited Valley City State University in January 2023 to review their collections from North Dakota. The specimens were from surveys conducted primarily for the North Dakota Department of Health (NDDH) and the North Dakota Department of Environmental Quality (NDEQ) using standard semi-quantitative techniques, which included sieving bottom substrates. They were collected between 1995 and 2020. The total number of records from North Dakota is 178.

A map (in PDF format) showing the distribution of all 795 of our unique sample sites is available as Figure 1.  No “absence stations” are shown.  If freshwater gastropods were not collected at a site, then no record resulted.  Our entire 1,474 record database is available (as an excel spreadsheet) from the authors upon request.

The taxonomy employed by the FWGNA project is painstakingly researched, well-reasoned and insightful.  Needless to say, it often differs strikingly from the gastropod taxonomy in common currency among casual users and most natural resource agencies.  First-time visitors looking for information about particular species or genera might profitably begin their searches with a check for synonyms in our alphabetical index.

> Results

The 33 species of freshwater gastropods we have confirmed from our four-state study area are listed in Table 1, both in [pdf] format and as a simple, sortable [excel] spreadsheet.  They are figured in the FWGGP gallery and distinguished on the FWGGP dichotomous key.  Ecological and systematic notes for each species are provided on dedicated pages, together with regional distribution maps. 

> Discussion

See our separate Discussion page for a comparison of the freshwater gastropod fauna documented here to expectation from the historical literature, with an analysis of the biogeographic trends demonstrated across our four-state study area and recommendations for further study. 

> Acknowledgements

Thanks to Kirsten Jensen, Mike Fritz & Steve Schainost, and Andre DeLorme for the invaluable help scouring agency and museum collections of Kansas, Nebraska, and North Dakota, respectively.  We also thank the many colleagues who provided personal collections and museum samples, especially our good friend Dr. Will K. Reeves, whose relentless field efforts filled in many gaps.

> References

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