Ecosystem significance of crayfishes and stonerollers in a prairie stream: functional differences between co-occurring omnivores

The ecosystem significance of crayfishes (Orconectes nais (Faxon) and O. neglectus (Faxon)) and central stoneroller minnows (Campostoma anomalum (Rafinesque)), was examined in a tallgrass prairie stream by estimating the trophic basis of production and consumption for each species. Annual ash-free dry mass production and production to biomass ratios of C. anomalum (260 mg m−2 y−1, 1.3) were lower than that of O. nais (719 mg m−2 y−1, 2.4) and O. neglectus (508 mg m−2 y−1, 2.1). Gut content analysis revealed no significant differences in the percentages of the various food items ingested by O. nais and O. neglectus, indicating they were functionally similar with respect to the types of organic matter processed in this system. We found a significant difference among seasons in the % of invertebrates in C. anomalum guts (p = 0.0001) and the % of algae in Orconectes spp. guts (p = 0.005), indicating the importance of measuring resource use throughout the growing season. Leaves contributed most to Orconectes spp. annual production (45%) followed by animal matter (30%), algae (19%), and amorphous detritus (6%). Algae contributed most to C. anomalum production (47%) followed by amorphous detritus (30%), animal matter (21%), and leaves (2%). Orconectes spp. consumed more leaf litter, filamentous green algae, and macroinvertebrates than C. anomalum, whereas C. anomalum consumed more diatoms. Crayfish and central stonerollers are both omnivores that function as important consumers and processors of algae and detritus in this tallgrass prairie stream, but each focuses on slightly different types of similar resources.