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growth showed that competition did occur. This lack of corroboration by diet <br />analysis is confusing, but may suggest an alternative hypothesis. That is, <br />the intensity of competition was consistent in all feeding regimes, but the <br />quality of competition changed. Wilson and Tilman (1991) presented this <br />hypothesis to explain plant competition along a nitrogen gradient: a similar <br />mechanism may be governing competitive interactions in our experiment. Fierce <br />competition in the lowest feeding regime may have manifested normally <br />insignificant, functional feeding differences that were reflected by reduced <br />diet overlap. At higher feeding regimes, functional differences may have been <br />of less importance, but competition remained intense because of differential <br />growth efficiencies. Thus, relative growth could have integrated effects of <br />two qualitatively different competitive mechanisms without reflecting a change <br />because intensity of competition remained relatively constant. <br />Possible implications <br />Some attributes that facilitate competitive superiority of one species <br />over another include: feeding efficiency, functional morphology, efficiency <br />of conversion of resource to biomass (growth efficiency), and body size <br />(Schoener 1983; Werner 1992}. Although identification and description of <br />characteristics that provided a competitive advantage were not objectives of <br />this research, results of this experiment allow insight into possible <br />mechanisms. Feeding efficiencies and functional morphology of the fishes were <br />similar based on their consumption of the same food items and ability to <br />capture brine shrimp nauplii. At the beginning of the experiment, Colorado <br />squawfish had a size advantage but grew slower than fathead minnow suggesting <br />that the size differential did not provide a competitive advantage. Thus, <br />20 <br />