BOTTOM-UP EFFECTS AND DENSITY DEPENDENCE DRIVE THE DYNAMIC OF AN ANTARCTIC SEABIRD PREDATOR-PREY SYSTEM

Abstract

ABSTRACTUnderstanding how populations respond to variability in environmental conditions and interspecific interactions is one of the biggest challenges of population ecology, particularly in the context of global change. Although several studies have investigated population responses to climate change, very few have explicitly integrated interspecific relationships when studying these responses. Here, we aim to understand the combined effects of inter- and intraspecific interactions and environmental conditions on the demographic parameters of a prey-predator system of three sympatric seabird populations breeding in Antarctica: the south polar skua (Catharacta maccormicki), and its two main preys during the breeding season, the Adélie penguin (Pygoscelis adeliae) and the emperor penguin (Aptenodytes forsteri). We built a two-species integrated population model (IPM) with 31 years of capture-recapture and count data, and provided a framework that allows estimating demographic parameters and abundance of a predator-prey system in a context where capture-recapture data are not available for one species. Our results showed that predator–prey interactions and local environmental conditions affect differently south polar skuas depending on their breeding state of the previous year. Concerning prey-predator relationships, the number of Adélie penguin breeding pairs showed a positive effect on south polar skua survival and breeding probability, and the number of emperor penguin dead chicks showed a positive effect on the breeding success of south polar skuas. In contrast, there was no evidence for an effect of the number of south polar skuas on the demography of Adélie penguins. We also found an important impact of sea ice conditions on both the dynamics of south polar skuas and Adélie penguins. Our results suggest that this prey-predator system is mostly driven by bottom-up processes and local environmental conditions.