Adaptations to a variable environment - feeding ecology, survival and physiology of southern rockhopper penguins

Abstract

Long-lived species exhibit a slow adaptation through natural selection and should rather adapt to rapid environmental changes through phenotypic plasticity, e.g. by showing behavioural changes. The degree to which species can adapt by phenotypic plasticity appears particularly critical for survival of a species in times of global climate change and other anthropogenic threats.In the framework of my PhD, I studied the reactions of southern rockhopper penguins (Eudyptes chrysocome) in response to environmental variability in terms of physiology, foraging behaviour and survival. Southern rockhopper penguins should be limited in their phenotypic plasticity compared to other species, as they are less mobile than flying seabirds and as they are feeding on low trophic level prey. These characteristics should make them more susceptible to changes in the food web. Populations of southern rockhopper penguins worldwide have declined dramatically in recent decades, and reasons for these declines remain unclear yet might be related to on-going climate changes. The southern rockhopper penguins' Subantarctic marine habitat is particularly affected by global climate change through an increase in sea surface temperatures (SST), and will likely experience changes in the wind regime, as the southern ocean west wind drift shifts polewards. How will southern rockhopper penguins react to such changes in their environment, which go beyond current environmental variability, in the future? To answer this question, I first studied the species' adaptations to its current environment, before focussing on the birds' reactions in foraging behaviour and survival to occuring environmental variability. Given that southern rockhopper penguins should be limited in their phenotypic plasticity, I expected them to show strong adaptations to their current environment and hypothesized that enhanced environmental variability negatively affects foraging behaviour and survival.My results indicate that southern rockhopper penguins are physiologically well adapted to colonial breeding as adults and juveniles show generally a strong immune status. This is particularly true as long as they are in a good body conditon. Furthermore, foraging trips during the incubation period allowed for rapid replenishment of body reserves, particularly in males, underlining the strong adaptations of this species to fasting and refeeding. I further found extraordinarily high annual survival rates in adults and juveniles under moderately cold to intermediate SST, which can be seen as an adaptation to stable, pre-warming environmental conditions. Outside a certain temperature range, however, adult survival rates decreased, which indicates a quadratic relationship between SST and adult survival. Furthermore, stable isotope data suggested a similar quadratic relationship between SST and the trophic level of prey taken by southern rockhopper penguins. These corroborating results indicate that southern rockhopper penguins show a narrow temperature optimum as part of their ecological niche.As a further result, foraging success depended heavily on wind direction and wind speed, with southerly to westerly (currently dominating) wind conditions enhancing foraging success.In summary, southern rockhopper penguins appear to be not well adapted to strong environmental variability and sensitive to global climate change. Considering global climate change scenarios and the results presented in this PhD thesis, one can expect that the predicted increase of SST and the southward shift of the west-wind drift will negatively affect foraging success and survival of southern rockhopper penguins, thus leading to further population declines. As global climate change is predicted to happen at an unprecedented pace, it makes susceptible species such as southern rockhopper penguins vulnerable to extinction.