Consequences of terrestrial top predator control by Patagonian sheep farmers for coastal marine food webs

Abstract

Most seabird species avoid predation by locating their breeding colonies in predator-free islands, inaccessible cliffs, capes, or on the mainland in Antarctica, the only continent without terrestrial predators. Departing from this general rule, a significant number of large Magellanic penguin (Spheniscus magellanicus) colonies exist nowadays in South American Atlantic mainland shores spanning a wide latitudinal range. Based on published radiocarbon dating of colonies, along with historical and archaeological records, we postulate that the current distribution of these colonies may be a response to predator eradication by sheep farmers. This would have made breeding habitats near marine food resources accessible and may have also reduced competition with neighboring colonies. We employed stable isotope analysis to estimate the penguin contribution to the diet of four pumas responsible for killing thousands of penguins in a breeding colony located within a coastal national park. Furthermore, we used a bioenergetic model to quantify the consumption of forage fish under different population distribution and abundance scenarios. We briefly discuss the implications of our results in the context of conservation policies aimed at establishing ecosystem baselines along the Patagonian shores.