Crepuscular Foraging: Do Big Meals Over Small Time Periods Lead to Stable Foraging Rates?

Large changes in the spatial distributions of organisms in lakes occur at crepuscular periods (ie. dawn and dusk), during which predators often experience higher foraging success on predictably moving prey. We ask whether these behaviours have consequences to predator-prey dynamics. We studied Lake Trout (Salvelinus namaycush) foraging behavior in two lakes, each with a different prey, Cisco (Coregonus artedii) or Freshwater Shrimp (Mysis sp.). Both Cisco and Mysis left spatial refuges at dusk to exploit foraging opportunities which exposed them to higher predation risk at dawn as both species attempted to regain their spatial refuges. The Cisco’s refuge is in schools and thus is sensitive to the abundance of individuals in the lake. By examining the Lake Trout functional response on Cisco we uncover a trade-off between foraging success on individuals at dawn under low prey density and success on schools in the late afternoon under high prey densities which leads to stable overall foraging rates. In the other lake, the Mysis refuge is restricted to a narrow band of substrate. We examine the collapse of a Mysis population as the refuge became constricted by limnological changes. Both examples demonstrate the role of crepuscular foraging in stabilizing foraging rates.