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50 FEEDING AND SPECIES INTERACTIONS One study looked at the gut contents of Ringed and Water Nymph crayfishes in Kings Creek, Kansas. There was little difference between the two and they consumed leaves (42%), animal matter (16%), filamentous algae (13%), detritus (23%), and diatoms (6%). Of these, leaves contributed 46% to annual production while animal matter contributed 29%. The animal matter was mostly other crayfish, dragonflies and mayflies. 55 A related study compared the stable isotope ( 15 N and 13 C) values in crayfish guts with their environmental values in the same stream. The values suggested that, as a whole, crayfish were acting as detrital and algal processors rather than predators. Small crayfish (<20 mm CL) appeared to be more dependent on algae and invertebrates than larger crayfish. The larger crayfish had isotope values that indicated dependence on leaves and FPOM (fine particulate organic matter). 56 PRODUCTION AND GROWTH The food habits study mentioned above also computed the biomass, growth and production of the Ringed crayfish in Kings Creek. Densities of Ringed crayfish ranged from 0.23 to 2.68 individuals/m 2 for juveniles (<25 mm) while adults ranged from 0.01 to 0.09/m 2. Most of the production occurred among the smaller crayfishes (<25mm CL) during the late summer and fall (July to October). Mean annual biomass was 244 ± 65 mg/m 2 and the mean annual production was 508 mg/m 2 which was 2.1 times the biomass. 55 IMPACTS This species has been introduced into New York and Oregon though impacts there are not known as yet. 42, 135 On the other hand, in Arkansas and Missouri they have been introduced into the Spring River from the White and Spring Rivers in the neighboring drainage. Here they appear to be displacing the native Cambarus hubbsi and Orconectes eupunctus. 150 DISTRIBUTION AND ABUNDANCE Up until now, the primary range of the Ringed crayfish has been described as southwestern Missouri and northwestern Arkansas with extensions into Kansas and Oklahoma. Disjunct populations were also known in north-central Kansas as well as western Kansas, northeast Colorado and southwest Nebraska. My work in Nebraska has shown that this range as shown in the map below is much larger than previously known. 205 There are two main population centers for the Ringed crayfish, one in the Ozark Interior Highlands and the second in the central Great Plains. A genetic study of the group to which the Ringed crayfish belongs placed the group's center of origin in the