Comparing 3-D visual and 2-D tactile encounter rates and their consequences for predation in benthic and pelagic habitats

Encounter rate models are important tools for evaluating and estimating trophic interactions between species. While encounter rate parameters have been measured for many freshwater pelagic fishes, most benthic fishes remain unstudied. Furthermore, encounter rate models are rarely compared, despite the many cases in which prey animals face predation risk from multiple types of predators. For example, the macroinvertebrate Mysis is exposed to both benthic and pelagic predation risk during diel vertical migration (DVM). We created a novel encounter rate model based on lateral line (“tactile”) foraging by sculpins (Cottidae) given the saltatory (stop-and-go) nature of their movement. We demonstrate the behavior of our tactile encounter rate model according to prey density, the detection radius of the predator, and the various movement characteristics that define saltatory motion. We also demonstrate how the model's behavior changes when detection radius depends on prey velocity. Then, we compare our newly derived tactile foraging model (2D) to a three-dimensional (3D) visual encounter rate model to compare predation risk for a Mysis population from two of their predators: the slimy sculpin Cottus cognatus (benthic, tactile predation) and the rainbow smelt Osmerus mordax (pelagic, visual predation) at both day and night. Tactile encounter rates were generally lower than visual rates for individual predators. However, population-level encounter rates at night were significantly greater in the benthic habitat than the pelagic habitat. Finally, we call for a greater focus on defining the encounter rates of benthic fishes to aid in the analysis of more complex ecological phenomena.