Abstract

While the effect of patch area on economic defendability has attracted considerable attention, there has been little research on patch shape. In addition, few studies have investigated the effects of resource defense from the perspectives of both defenders and intruders. Hence, I manipulated food patch shape independent of patch area (square, 13.6 x 13.6 cm; rectangular, 46.5 x 4.0 cm; elongated, 93.0 x 2.0 cm) and group size (three, six, twelve fish) in a 3 X 3 factorial design. I tested the predictions that the frequency of aggression, degree of resource monopolization and size variation within groups would decrease as patch perimeter and group size increased. As predicted, with increasing patch perimeter the frequency of aggression and the degree of resource monopolization decreased, but there was no change on growth depensation (size variability). Increasing the number of fish decreased the frequency of aggression, degree of resource monopolization, leading to less size variation within groups. My study is one of the first factorial studies to manipulate the actual perimeter of the food patch to show that increasing the patch perimeter had the same effect as increasing group size on the economic defendability of a patch. My study also demonstrated that it is important to the theory of resource defense to examine the foraging success of both the defenders and intruders.