423J. N. Am. Benthol. Soc., 2003, 22(3):423–441q2003 by The North American Benthological SocietyEcosystem significance of crayfishes and stonerollers in a prairiestream: functional differences between co-occurring omnivoresMICHELLEA. EVANS-WHITE1ANDWALTERK. DODDSDivision of Biology, Kansas State University, Manhattan, Kansas 66506 USAMATTR. WHILESDepartment of Zoology, Southern Illinois University, Carbondale, Illinois 62901-6501 USAAbstract. The ecosystem significance of crayfishes (Orconectes nais (Faxon) and O. neglectus (Faxon))and central stoneroller minnows (Campostoma anomalum (Rafinesque)), was examined in a tallgrassprairie stream by estimating the trophic basis of production and consumption for each species. An-nual ash-free dry mass production and production to biomass ratios of C. anomalum (260 mg m22y21, 1.3) were lower than that of O. nais (719 mg m22y21, 2.4) and O. neglectus (508 mg m22y21, 2.1).Gut content analysis revealed no significant differences in the percentages of the various food itemsingested by O. nais and O. neglectus, indicating they were functionally similar with respect to thetypes of organic matter processed in this system. We found a significant difference among seasonsin the % of invertebrates in C. anomalum guts (p50.0001) and the % of algae in Orconectes spp. guts(p50.005), 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. con-sumed more leaf litter, filamentous green algae, and macroinvertebrates than C. anomalum, whereasC. anomalum consumed more diatoms. Crayfish and central stonerollers are both omnivores thatfunction as important consumers and processors of algae and detritus in this tallgrass prairie stream,but each focuses on slightly different types of similar resources.Key words: Orconectes, central stonerollers, omnivory, growth rate, secondary production, gut con-tents.Crayfish and central stonerollers (Campostomaanomalum (Rafinesque)) are widespread andabundant benthic omnivores in North Americanstreams (Momot 1984, Matthews et al. 1987).These organisms often co-occur in midwesternstreams in the United States and are thought toconsume similar food resources. However, fewcomparative data exist on the functional role ofthese 2 omnivores within the same stream sys-tem.Crayfish can play important roles in structur-ing benthic macroinvertebrate and algal com-munities (Creed 1994, Charlebois and Lamberti1996, Parkyn et al. 1997) as well as in organicmatter processing and energy flow (Huryn andWallace 1987, Whitledge and Rabeni 1997). Anexamination of the trophic basis of production1Winner of the WILDCO Student Award for theBest Oral Presentation in Basic Research at the 49thAnnual NABS Meeting, La Crosse, Wisconsin, 2–7June 2001. Present address: Department of BiologicalSciences, University of Notre Dame, Notre Dame, In-diana 46556 USA. E-mail: [email protected] crayfish in a Missouri stream indicated thatanimal (29–51%) and detrital (32–56%) materialcontributed the most to secondary production,followed by algae (14–18%) (Whitledge and Ra-beni 1997). In addition, Whitledge and Rabeni(1997) found crayfish were important consum-ers of animal matter, detritus, and algae whencompared to other invertebrates in this system.Similar information on the role of C. anomalumin organic matter processing and energy flow islacking, even though these fish can be extremelyabundant in small and medium-sized streamsand sometimes dominate the fish communityboth numerically and in terms of biomass(Schmulbach 1953, Lennon and Parker 1960,Beets 1979, Matthews et al. 1987).Studies of C. anomalum have focused primar-ily on its ability to structure benthic algal com-munities and to reduce algal biomass in prairieand Ozark mountain streams (Power et al. 1985,1988, Gelwick and Matthews 1992, 1997, but seeVaughn et al. 1993). In addition to algae, C. an-omalum also ingests animal matter and a signif-424 [Volume 22M. A. EVANS-WHITE ET AL.icant amount of detritus (Kraatz 1923, Fowlerand Taber 1985, Burkhead 1980). However, therelative importance of these food sources to C.anomalum production is not known. In addition,few investigators have measured C. anomalumgrowth rates (Schmulbach 1953, Lotrich 1973) orsecondary production (Lotrich 1973) in a waythat can be compared among streams andamong different components of stream com-munities (e.g., macroinvertebrates).Recent investigations in a prairie stream pro-vided comparative data for the roles of crayfishand C. anomalum in material processing. Doddset al. (2000) quantified N cycling in KingsCreek, a tallgrass prairie stream located on Kon-za Prairie Biological Station (KPBS), and foundthat crayfish (Orconectes spp.) played a more sig-nificant role than other stream macroinverte-brates and C. anomalum in algal and detrital Nprocessing. However, this experiment spannedonly 2 mo of the growing season (April andMay). In a related study, natural abundance iso-tope data (15Nand13C) collected over many sea-sons from the same stream suggested that cray-fishes might be more dependent than C. anom-alum upon algal and detrital resources forgrowth (Evans-White et al. 2001).The objective of our study was to compare theecosystem significance of Orconectes spp. and C.anomalum in Kings Creek by estimating the tro-phic basis of their production and comparingconsumption of food resources. We addressed 2component objectives: 1) to estimate Orconectesspp. and C. anomalum biomass, growth, and pro-duction in Kings Creek over 1 growing season,and 2) to determine food sources used by eachomnivore in Kings Creek by examining gut con-tents of Orconectes spp. and C. anomalum.Wepredicted that algal and detrital food sourceswould be more important to the production ofcrayfish than C. anomalum given previous evi-dence from natural abundanced15Nandd13Cstudies. In addition, we predicted crayfishes, be-cause of their apparently higher biomass in thisstream, would be more significant than C. an-omalum as processors of algae and detritus.MethodsStudy areaKings Creek drains;1059 ha of KPBS, a tall-grass prairie preserve located in the Flint Hillsregion of northeastern Kansas (Fig. 1). The avail-ability of detrital and algal