Changing diets over time: knock-on effects of marine megafauna overexploitation on their competitors in the southwestern Atlantic Ocean

Abstract This study compares the δ 15 N values and trophic position of two seabird species throughout late Holocene in three regions southwestern Atlantic Ocean to assess hypothesis that decimation megafauna led changes mesopredators. Modern ancient mollusk shells were also analyzed account for isotopic baseline through time. Results revealed modern Magellanic penguins have higher than their conspecifics regions, after controlling baseline. was true Imperial shags compared with unidentified cormorants/shags from areas where specimens recovered (southern Patagonia Beagle Channel). Such temporal variability might be caused by non–mutually exclusive processes: decreased availability pelagic squat lobster resulting decreasing primary productivity Holocene, increased small fishes sequential depletion other piscivores (South American fur seal sea lion Argentine hake) since eighteenth century, modification migratory patterns penguins. Although disentangling relative contribution all those processes is impossible at this time, results reported here demonstrate ecology has undergone major Holocene.