Species Packing and Niche Complementarity in Three Sunfishes

This study develops a method to relate foraging theory to species-packing theory. Cost curves, which rank prey by their cost-benefit ratio to the predator, are quantitatively determined for three species of sunfishes (Centrarchidae) that differ systematically in their morphology. The cost curves are used to estimate extremes in the range of food sizes in the diet of a fish given its size and morphology (species). The distribution of available resources is found to be lognormal and, with the above diet ranges, permits the calculation of the niche width and location on the food size axis for individual fish. The extremes in niche width and location for size-distributed populations of these species are then determined by combining and weighing the contribution of each size class. Overlap on the food size coordinate for populations of Lepomis macrochirus and Micropterus salmoides is shown to be very close to that predicted by current species-packing theory. It is predicted that these species occupy similar habitats and segregate on the food size axis while the third species, which is intermediate in morphology (L. cyanellus), should be excluded from these habitats and show complementarity on niche dimensions. Data on habitat utilization of these species from natural communities confirm these predictions. Species packing on the food size coordinate is discussed in relation to species populations which are size distributed.