Responses to the Foraging/Predation Risk Trade-Off and Individual Variability in Population-Level Fitness Correlates

Foraging under the influence of interspecific interactions such as competition and predation risk can have effects on the energetic reserves of the forager. Measurements of condition in species such as fish are usually correlated with individual fecundity and, hence, fitness. From work in two study systems in which predation risk regulates habitat selection and foraging behavior of benthic fishes I examined whether risk dependence led to reduced variability in fish condition. In field populations of cottid fishes, observed in an estuarine system and in the near-shore habitat of an oligotrophic lake, I found that individuals that experienced higher predation risk showed reduced variability in CI. Estuarine cottids with high food availability and substantial predation risk varied less in CI among individuals than in the associated tidal creek. In the lake, where there is considerable heterogeneity in benthic food resources, a related cottid species showed reduced variation in CI with increasing predation risk from adults. Finally, I examine my previous experiments showing that the estuarine species is limited in its use of high resource availability in estuaries by competition and predation risk. Here I found that variability in individual condition index (CI) was higher when intraspecific and interspecific competition increased and did not increase in the face of predation risk. 1. Introduction Research into how animals select habitats in heterogeneous environments has been informed by how the complementary use of safe, relatively unproductive habitats or patches and more productive yet very risky patches influences overall fitness [1, 2]. By using food and safety from predation risk in a complementary manner, foraging animals benefit from time spent in safety (i.e., in less risky habitats/patches or through vigilance behaviors; e.g., [1, 3]) when the marginal value of food obtained no longer exceeds the cost of predation. Field measurement of the forager’s giving up density (GUD) facilitates study of the behavioral optimization of this trade-off (e.g., [1, 2, 4–6]). GUDs are applicable to a suite of predation-avoidance behaviors such as vigilance [2, 7] and apprehension [2, 8] and represent the marginal value of food in terms of the risk involved in obtaining it (e.g., [1, 3, 9, 10] and reviewed in [11]). A forager’s present condition (e.g., [4, 12–14]) and the density-dependent distribution of predators [15] affect the amount of risk taken to obtain food, leading to variation in that condition through time (e.g., [12, 16]), in turn affecting subsequent