Alternating ecosystem states driven by an invasive fish in a life-history intraguild predation system

Prey species that compete with or consume early-life stages of their primary predator (i.e., life-history intraguild predation (LHIGP)) can generate alternate ecosystem states and distinct shifts in predator demographics. Identifying ecological conditions underlying alternate states can inform adaptive management of LHIGP-driven ecosystems and fisheries. We developed a time-varying, stage-structured population modeling framework to explore the dynamics of a walleye ( Sander vitreus) population supported by invasive rainbow smelt ( Osmerus mordax), a widely introduced forage fish that can negatively affect walleye recruitment. Our model identified two distinct and cyclic states over a 42-year time-series. The first was characterized by low smelt abundance, elevated Daphnia density and walleye recruitment, but poor walleye growth and survival to larger size, while inverse patterns characterized the second state. Strong state-dependent shifts in predator vital rates and population structure emphasized the need for flexible management approaches (e.g., stocking, harvest regulations) to maintain fisheries quality and population sustainability. Our modeling framework is broadly applicable to understanding the dynamic nature and informing adaptive management of nonstationary systems, such as those characterized by LHIGP.