The effect of body size on prey choice by Rivulus luelingi Seegers 1984 (Aplocheiloidei: Rivulidae)

The effect of body size of Rivulus luelingi (10-15, 20-25, 30-35, 40-45, 46-50 mm length classes) on predation of three size class combinations of Culex sp larvae (small-medium, small-large, medium-large) was studied in the laboratory by means of analyses of preference, specific overlap, and actual number of prey eaten. The smallest experimental R. luelingi size class (10-15 mm) was gape limited. Experimental diets were affected by prey choice and morphological constraint. Preference for the smaller prey, in each prey type combination, was negatively correlated with predator body size, and the converse was true for the larger prey. Preference for any prey size depended on the available prey distribution. There was a correlation between the number of each prey size eaten and predator size in each prey size combination, except for the small prey in the small-medium combination. Specific overlap analysis revealed asymmetries in diet overlap. Feeding success increased non-linearly with R. luelingi body length for two prey size distributions; longer individuals had a disproportionally high feeding success. Preference analysis was more accurate than either specific overlap or actual number of prey eaten. The three kinds of analysis resulted in blocks of contiguous size classes with similar resource utilization, which were considered to have a high chance of interacting competitively.