Scaling up from Drift Foraging to Population Responses

Drift foraging models often have the objective of predicting an individual fish’s energy intake, but what if the objective is to predict population responses to changes in habitat and food? How would a foraging model be different if it is part of an individual-based population model? We used drift foraging as the lowest-level process in an individual-based model (called inSTREAM) of salmonid population responses to flow, temperature, and turbidity regimes; and to changes in physical habitat. A set of “characteristic patterns” in foraging at the individual and population levels was used to design and test the model. For this application, foraging models must have several characteristics not always considered when focussing only on energy intake; e.g., they must represent effects of fish size, temperature, and turbidity. High resolution is not necessarily important, but representing competition, predation risk, and habitat selection behavior are. Sensitivity analysis identified particularly important foraging parameters—some expected (e.g., metabolic rates) and others unexpected (e.g., how prey detection varies with fish size). Research needs include better empirical support for bioenergetics relations, better understanding of foraging by very small fish, and understanding of how predation risk varies with habitat. Models of non-drift foraging are also needed.