Role of satiation in the functional response of a piscivore, largemouth bass (Micropterus salmoides)

We evaluated whether satiation regulates the predation rates of a piscivore, largemouth bass (Micropterus salmoides), in natural settings. A functional response model indicated that predation rates can be reduced by satiation when mean prey density is high or when prey encounters are highly patchy. We then used bioenergetics modeling to estimate the predation rates of individual bass in four lakes during a 16-year period and used stomach content mass in diet samples to evaluate the variability in daily predation rates. Predation rates, expressed as the proportion (p) of the maximum daily consumption rate, were low (mode = 0.3, mean = 0.4). Stomach fullness (s), expressed as the proportion of the stomach fullness associated with the maximum sustainable consumption rate, was highly variable, and 13% of all bass diets had s > 1, indicating that bass could opportunistically forage at rates exceeding their maximum sustainable rate. The low predation rates and the ability to consume prey at rates exceeding the maximum sustainable rate make it unlikely that satiation was an important constraint on bass predation rates. Thus, satiation effects widely represented in modeling studies may be a rare component in piscivore-prey interactions, while prey behavior may be a more important component governing predation rates.