Modeling Species-Specific Predation Risk: Discerning Risk-Avoidance Strategies within a Diverse Pelagic Planktivore Community

Declining light and increasing turbidity reduce reaction distances, search volumes, and prey encounters at disproportionately higher rates for piscivores than for planktivores.  However, given a predator-prey encounter, capture success for piscivores improves in degraded optical conditions.  These asymmetric threshold responses interact with vertical light gradients, seasonal and inter-basin differences in productivity, thermal stratification and other processes to create complex spatial-temporal patterns of distribution, foraging success, and predation risk.  These differential effects on foraging success and risk can provide a mechanistic framework for evaluating the drivers of diel vertical migration (DVM) at multiple trophic levels.  Planktivores must balance the need to feed and grow with the metabolic demands of foraging in different habitats and associated risk of predation within those habitats.  In addition to energetic status and life history constraints, the extent to which a particular species avoids or utilizes risky foraging habitat should reflect morphological attributes (e.g., size, presence of spines, armoring, and transparency) that influence perception of risk, or limit visual detection by contrast-based piscivores.  Diversity within these factors can generate divergent DVM trajectories among species within planktivore communities, which has important implications for density-dependent processes and the vulnerability of each species to predation.  Here, we use a mechanistic approach to examine the predation risk associated with different planktivorous prey fishes in Lake Washington, based on differences in seasonal depth-distribution, body size, transparency, and morphology.  We use this information to discern foraging-predator avoidance strategies across an array of taxonomically divergent species.