The growth benefits of aggressive behavior vary with individual metabolism and resource predictability

Differences in behavioral responses to environmental conditions and biological interactions are a key determinant of individual performance. This study investigated how the availability and predictability of food resources modulates the growth of animals that adopt different behavioral strategies. Results show that, irrespective of the feeding regime, the growth of juvenile brown trout increased with the expression of active foraging behavior and, similarly, with increasing use of shelter. Conversely, territorial aggressive behavior only promoted growth when food resources were spatially and temporally predictable, and only for individuals that had high metabolic rates (when compared with their low metabolic rate siblings). Thus, this study shows that only certain behaviors are associated with variation in the physiology of individuals. Moreover, only certain behaviors associate differently with growth under different environmental conditions. These results are partially consistent with the hypothesis that environmental variability promotes the coexistence of alternative behavioral phenotypes. However, some behaviors enhanced growth irrespective of feeding regime, and we did not identify a set of conditions where fish with low resting metabolic rate (RMR) outperformed their high RMR siblings. Hence, additional layers of environmental variation are likely to be required for individuals with low RMR to show maximal growth performance.