RELATIVE COMPETITIVE SUCCESS OF UNEQUAL COMPETITORS CHANGES WITH OVERALL DENSITY

A group of 10 individually identifiable cichlid fish were used in a tw o-patch continuous input situation to examine the effect of density on relative competitive success of unequal competitors. Sutherland and P arker have proposed that relative intakes of unequal competitors can e ither remain constant across densities or that at higher densities bet ter competitors will achieve higher gain rates. They also suggest that past continuous input situations have tended to fit the former predic tion. We examined the influence of competitive ability on intake at di fferent densities resulting from movement of fish between the two patc hes. This showed that contrary to the predictions of any model, in our system the best competitor did better relative to other individuals a t lower densities, whereas the poorest competitor did better at higher densities. Fish of intermediate ability showed an intermediate effect of density on intake. As density increased there was a decrease in th e difference between individual intakes, rather than the increase pred icted by Sutherland and Parker's model. We suggest that this finding m ay be the result of competition switching from a contest between indiv iduals at low density to a scramble for resources at higher density.