The Niches of Two Sympatric Softshell Turtles, Trionyx muticus and Trionyx spiniferus, in Iowa

Abstract

This study was conducted throughout Iowa beginning in the lower reaches of each river system and working upstream into the headwaters and small tributaries. Trapping with baited hoop-nets (Legler, 1960) was begun in 1969 and continued through 1974. Trammel nets (15.25 x 1.25 m) were also used, and animals were collected by hand as described by Webb (1962). Basking sites were described and the number and kind of basking turtles, air and water temperatures, and time of basking were recorded. Turtles collected for stomach content analyses were immediately killed by cephalic injection of 95% ethanol and injection of 15% formalin into the stomachs. Shells and soft parts were preserved separately in 10% formalin as described by Christiansen and Dunham (1972) and all preserved specimens were deposited in the Drake University Research Collection. Approximate percentages of identifiable insects, unidentifiable insect parts, other identifiable animals and parts, miscellaneous animal material, plant material, sand and gravel, and debris were determined volumetrically. Significance of difference between food eaten by the two species was estimated at the 5% level with the help of 2 x 2 Chi-square and Student's t tests. Radiotelemetry observations were made in three abandoned, flooded sand pits adjacent to the Cedar River on the north side of Muscatine County highway F-70, 11.2 kilometers northwest of Muscatine, Iowa. During high water these ponds were continuous and connected to the river. They lacked rooted vegetation, but had a variety of fish. The turtle fauna included Graptemys pseudogeographica, Chrysemys picta, Chelydra serpentina, and the two Trionyx species. In 1974, one