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~, <br />This experiment focused on competition for food between larval Colorado <br />squawfish and larval fathead minnow. Early life stages of Colorado squawfish <br />co-occur with fathead minnow and share habitat and food resources. Young <br />Colorado squawfish, and all life stages of fathead minnow, inhabit shallow <br />near-shore habitats (e.g., backwaters and side channels) and feed on <br />zooplankton, chironomid larvae, and detritus (Vanicek and Kramer 1969; <br />S. J. Grabowski and S. D. Hiebert, unpublished report). At 20 to 30 mm total <br />length, Colorado squawfish begin to consume other small fishes. Thus, intense <br />competition for food between Colorado squawfish and fathead minnow may occur <br />during a relatively short developmental period ranging from onset of exogenous <br />feeding to commencement of piscivory in Colorado squawfish. <br />It has been shown that growth is positively related to fitness and <br />competitive ability (Werner 1976; Mittlebach 1981; Persson 1991). Our <br />experiment was designed to compel the fishes to compete for zooplankton so <br />that the effects of competition on growth could be observed. We determined <br />the outcome of interspecific competition for food between larvae of Colorado <br />squawfish and fathead minnow by (1) estimating relative growth of each species <br />in single-species assemblages and mixed-species assemblages; (2) estimating <br />effects of intraspecific competition; (3) estimating effects of interspecific <br />competition after subtracting effects of intraspecific competition; <br />(4) determining the symmetry of competitive interactions and, if asymmetric, <br />identifying which species was most adversely affected; and (5) confirming <br />results by studying the relation between diet overlap and resource <br />availability. <br />6 <br />