TEMPORAL CLUMPING OF FOOD ARRIVAL REDUCES ITS MONOPOLIZATION AND DEFENSE BY ZEBRAFISH, BRACHYDANIO-RERIO

The hypothesis that monopolization and defence of resources decreases as the temporal clumping of resource arrival increases was tested using groups of six zebrafish competing for 300 Daphnia pulex prey. Clumping was varied by controlling the duration of the period (3, 10, 30, 100, or 300 min) over which the prey arrived through a single, centrally located feeding tube, which was vigorously defended by the dominant fish in each group. Resource monopolization, measured by the variance/mean ratio of prey eaten per individual per trial within a group, increased as trial duration increased. The share going to the most successful fish also increased with trial duration. Resource defence by the dominant fish, measured as total chases per trial, increased as trial duration increased, but number of chases per min reached a peak in the 30-min trial. The number of competitors near the feeding tube decreased with trial duration, suggesting that defence became more effective in longer trials. In short trials, dominant fish were not necessarily the most successful individuals, but with increasing trial length the proportion of groups in which dominant fish were the most successful and the proportion of prey taken by the dominant fish in each group increased. This is the first direct evidence that an increase in monopolization produced by a decrease in clumping of resource arrival occurs because of more effective defence. © 1992 The Association for the Study of Animal Behaviour.