| Many variables, including characteristics of the environment and those of the fish themselves, can affect survival of young fish. I explored how sources of variability, both those intrinsic and extrinsic to the fish, affected larval performance and survival. With a simulation model, I found that variation in feeding ability and growth capacity among fish can regulate survival to the same extent as changes in the environmental factors that historically have been considered most important. Both model and laboratory results indicate that how fish process food (growth capacity) rather than their ability to obtain it (feeding) had bigger effects on survival. Even very small differences in growth capacity had large effects on survival. For smaller fish ({dollar}<{dollar}15 mm), differences within species had a larger effect on growth and consumption rates, but differences among species were more important for larger fish, suggesting a focus on individual growth variability for larvae and on both species and individual differences for juveniles.; Individual growth variability within a cohort can be substantial and depended on food level; after just 3 weeks of growth up to 30% of the fish in experimental laboratory cohorts changed size rank and fish were more likely to switch rank when food levels were higher. At low food level, smaller fish in the cohort had higher mortality rates and lower growth rates than did larger fish, the opposite pattern than at high food.; Individual feeding history did not affect times to mortality due to starvation, but fish feeding intermittently before starving died slightly heavier than fish feeding continuously. Also, proportional mass loss up to starvation was independent of initial mass for any one feeding history.; Spatial patchiness of food resources can also generate variable individual growth rates. Model results suggested that not just the average prey density but also the intensity of patchiness can have a substantial impact on survival and that the effects of patchiness and overall food level on survival are not independent. Finally, the effect of the other key extrinsic factor, predator size, also depends on more than just a description of the average; depending on the predator size distribution, survival can vary up to 50% with different predator size variances. |
