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was the effect of interspecific competition (alpha = .05 for all statistical <br />comparisons). Values of d not significantly different from zero suggest that <br />relative growth was equivalent in mixed-species assemblages and in <br />single-species assemblages; negative values suggest that relative growth was <br />reduced in mixed-species assemblages. <br />Conclusions of t-tests were confirmed by regressing d as a function of <br />relative abundance (i.e., percent Colorado squawfish) within each feeding <br />regime. A significant regression confirmed that relative growth was different <br />in mixed-species assemblages compared to single-species assemblages .and that <br />the relationship was a function of relative abundance. Slope of the <br />regression line described the response of each species to interspecific <br />competition. For example, if d for species A decreased with increasing <br />relative abundance of species B, it was concluded that growth of species A was <br />reduced by interspecific competition. <br />Competitive ability of Colorado squawfish and fathead minnow was <br />compared using an index that is identical to the relative crowding coefficient <br />used by de Wit (1960}. Competitive ability as defined by Snaydon (1991) is <br />the ability of one species to obtain and use limiting resources, when grown in <br />mixed assemblages with another species, compared with its ability to obtain <br />and use those resources when grown in single-species assemblages. Competitive <br />ability was calculated based on mean relative growth in each experimental <br />treatment, using the formula: <br />CA = l og~o ~ (~f ~ G ~) ~ (Gf~ I Gff) ] ~ <br />11 <br />