Hurry Up and Wait: Growth of Young Bluegills in Ponds and in Simulations with an211 Individual-Based Model

摘要

The growth of young-of-the-year bluegills Lepomis macrochirus was measured in six211u001eexperimental ponds and simulated with an individual-based model. In the ponds the 211u001eyoung bluegills grew at a rate of about 0.6 mm/d for 3-4 weeks. An abrupt 211u001ereduction in growth rate to about 0.2 mm/d occurred when total zooplankton 211u001edensity (exclusive of rotifers) decreased below about 50 organisms/L, and growth 211u001erate decreased to nearly zero by September. The model included daily foraging for 211u001eseveral sizes of open-water or benthic prey and a revised set of bioenergetics 211u001eparameters for bluegill. The simulations suggest that the initally rapid growth 211u001erate was near the limit set by maximum daily ration; the fish may have obtained 211u001efull rations even with suboptimal foraging during this phase. Over a wide range 211u001eof fry densities, the time of growth reduction and the average final fish size at 211u001ethe end of the growing season were strongly density dependent, both in the 211u001esimulations and the ponds. Two natal cohorts started 10 d apart in the 211u001esimulations. The size-frequency distributions produced by this individual-based 211u001emodel showed that these two cohorts remained distinct at starting densities below 211u001eabout 1 fish/cu m, but tended to overlap in size at higher densities.