7760 - Laserfiche WebLink

Home Browse Search

Introduction Quantitative study of resource competition has been frustrated by an inability to separate effects of intraspecific and interspecific competition (Connell 1983; Schoener 1983; Strong et al. 1984; Diamond and Case 1986; and Underwood 1986). Even for the simplest case of interspecific competition (i.e., two-species assemblage), few studies allow unconfounded interpretation if experimental design and analysis are critically evaluated. Two types of experimental design are commonly used to study competition in two-species assemblages (1) replacement designs, and (2) additive designs. Strengths and weaknesses of these approaches have been summarized (de Wit 1960; Marper 1977; Connolly 1986, 1988; Underwood 1986; Rejmanek et al. 1989; Snaydon 1991), and both approaches have a degree of intuitive appeal but are either confounded or difficult to interpret. Snaydon (1991) noted "there has been no consensus on the nature of the problems which replacement desi4ns~ose, nor of how they might be solved; neither has there been anv clear recognition of the role that additive designs might play" and suggested that bivariate factorial designs have advantages over traditional methods. We used an experimental approach that incorporated positive attributes of replacement and additive designs to study resource competition between larvae of federally endangered Colorado squawfish, Ptvchocheilus Lucius, and a widely distributed non-native species, the fathead minnow, Pime~hales promelas. The method is equivalent to an incomplete bivariate factorial design and allows unconfounded, straight-forward interpretation of intra- and interspecific competitive effects. It also has the advantage that if competition occurs, the response of each species is consistent with that predicted by ecological theory. Theoretically, when two species compete for limited resources, the interaction 4