Ecosystem consequences of wolf behavioural response to climate

Because apex predators exert considerable influence on the structure and function of top-down ecosystems, their responses to climate may shape responses at lower trophic levels. Previous reports of trophic cascades and ecosystem dynamics induced by predators have focused on changes in their abundance, whereas we investigated whether changes in predator behaviour could precipitate cascades of similar ecological scale. Here we report the ecological consequences of predator behavioural response to global climatic variation using 40 years of data on wolf predation from Isle Royale, USA, where wolves limit abundance of moose, which limit productivity of fir trees. In response to increases in winter snow related to the North Atlantic Oscillation, wolves hunted in larger packs and, consequently, tripled the number of moose killed per day compared with less snowy years when they hunted in smaller packs. Following increased predation rates, moose abundance declined, and, following release from heavy browsing, growth of understory fir increased. Hence, cascading behavioural responses of apex predators may be a substantial link in the pathway from climatic change to ecosystem function.