Ecosystem consequences of wolf behavioural response to climate

Because apex predators exert considerable influence on the structure and fu nction of top-down ecosystems(1-3), their responses to climate may shape re sponses at lower trophic levels(4). Previous reports of trophic cascades an d ecosystem dynamics induced by predators have focused on changes in their abundance(5-8), whereas we investigated whether changes in predator behavio ur could precipitate cascades of similar ecological scale. Here we report t he ecological consequences of predator behavioural response to global clima tic variation using 40 years of data on wolf predation from Isle Royale, US A, where wolves limit abundance of moose(9), which limit productivity of fi r trees(10). In response to increases in winter snow related to the North A tlantic Oscillation, wolves hunted in larger packs and, consequently, tripl ed the number of moose killed per day compared with less snowy years when t hey hunted in smaller packs. Following increased predation rates, moose abu ndance declined, and, following release from heavy browsing, growth of unde rstory fir increased. Hence, cascading behavioural responses of apex predat ors may be a substantial link in the pathway from climatic change to ecosys tem function.