GROWTH-RATE VARIATION AND LARVAL SURVIVAL - INFERENCES FROM AN INDIVIDUAL-BASED SIZE-DEPENDENT PREDATION MODEL

We used an individual-based Monte Carlo simulation model to explore ho w changes in the mean and variance of growth rates of individuals in a larval fish cohort interact with size-dependent predation to affect t he number and characteristics of individual survivors. Small changes i n initial cohort mean growth rate can change survival over the first 6 0 d of life 10- to 30-fold. But when variance in growth rate among ind ividuals is high, survival can be substantially higher than expected f rom the initial mean cohort growth rate. Selection for faster-growing individuals becomes stronger with increasing variance and increasing p redation rate. In some cases, >80% of the survivors may come from the upper 25% of the initial growth rate distribution, and the mean growth rate of the survivors may exceed twice the initial mean growth rate. When individual growth rates change from day to day rather than remain ing constant, the contribution of atypical individuals is accentuated even further. Counter-intuitively, most of the selection for faster-gr owing individuals happens only after the majority of mortality has alr eady taken place. These results suggest that interactions between indi vidual variability and selective mortality may have important cohort-l evel implications for survival in fishes.