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

and regression analysis provided a more detailed description of quantitative
relationships.
Regression analysis showed that the response of d as a function of
relative abundance within each feeding regime was variable (Table 2). For
Colorado squawfish in the two highest feeding regimes, there was a significant
reduction in growth as the relative abundance of fathead minnow increased. In
the lowest feeding regime, the regression was not significant, suggesting that
there was no relationship between Colorado squawfish growth and relative
abundance, or that the relation was not detected by statistical analysis. The
response of fathead minnow in the highest feeding regime was similar to that
of Colorado squawfish: growth declined as the relative abundance of the
competitor increased. No statistically significant relationship was detected
in the intermediate feeding regime. In the lowest feeding regime, growth of
fathead minnow increased significantly with relative abundance of the
competitor. This response is inconsistent with ecological theory because it
implies that fathead minnow crew faster in mixed- than in single-species
assemblages (i.e., the inter ~~~ion had the form +/0). The cause of this
anomalous response is uncer_~rn, but may have resulted from failure to
maintain initial fish densities and relative abundances in the lowest feeding
regime. In that regime, fathead minnow survival ranged from 22 % to 53 %.
Because growth was slow in the lowest feeding regime, deviations of food
ration due to mortality may have had relatively large effects.
Competitive ability
In contrast to t-test and regression methods which detected competitive
effects by intraspecific comparisons of growth in mixed- and single-species
15