Data and code from: Prey detection by a stepwise visual template matching mechanism

Prey capture success by a predator can be improved by the formation of a search image, and recent experience with a prey item provides a visual template to which subsequent potential prey are compared. Following observations of distinct trout feeding responses to drifting mayflies in a large western U.S. river in the same month across two successive years, we developed a set of experiments to test if changing ratios of sequentially delivered prey of the same species but different body sizes caused a shift in trout feeding response. We discovered that large-sized focal prey were always consumed. Comparing predation on large- versus small-sized prey (137% length difference), few small prey were consumed, but when comparing large- versus medium-sized prey (99% length difference), all medium prey were consumed. When small-sized prey, initially rejected, were compared with the newly established medium-sized focal prey (57% length difference), all medium and small prey were consumed. When trout previously exposed to small prey were subsequently fed only large prey, fish memory of the small prey lasted for at least 14 days. These results provide evidence that predator search image formation for novel prey requires a dynamic stepwise neural template matching process. We discuss how this mechanism could be used by many consumers to optimize foraging, with implications for predator and prey population dynamics, such as the persistence of rare prey and its role in selection on prey phenology to minimizes predation of different size classes, species, or both.