7760

• UCREFRP Catalog Number: 7760
• Author: Beyers, D. W., R. T. Muth and M. S. Farmer.
• Title: Experimental Evidence of Competition Between Larvae of Colorado Squawfish and Fathead Minnow.
• USFW Year: 1994.
• USFW - Doc Type: \
• Copyright Material: NO

subjected to Shapiro-Wilk's Test for normality and Bartlett's Test for
homogeneity of variance (Zar 1984). Subsequently, relative growth was logo
transformed to stabilize variance for statistical procedures.
Density-dependent intraspecific competition was studied by analyzing the
relation between relative growth and feeding regime for Colorado squawfish and
fathead minnow in single-species assemblages. Regression analysis was used to
fit relative growth as a function of feeding regime. A significant regression
suggested that intensity of intraspecific competition varied with zooplankton
availability. Regression equations also allowed prediction of relative growth
over a range of feeding regimes: these estimates were used in analysis of
interspecific competition.
Effects of interspecific competition were estimated by comparing
relative growth of fish in mixed- and single-species assemblages, at identical
species-specific per-capita feeding regimes (Figure 1). For example, for the
experimental treatment illustrated in Figure 1, which comprised 62 Colorado
squawfish and 63 fathead minnow for a total density of 125 fish per aquarium,
the response of each species was compared to that estimated from
single-species regression equations at a density of 62 or 63 fish per
aquarium, respectively. The difference between relative growth in
mixed-species assemblages and single-species assemblages was tested by
calculating a one-sample t-statistic, and comparing it to a two-tailed
Student's critical value (Zar 1984). Relative growth in mixed-species
assemblages was the observed value; relative growth in single-species
assemblages was the expected value. A difference (d), where:
d = observed relative growth - expected relative growth,
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