SFB-TRR 212

Niche conformance as a mediator of niche choice in Galápagos sea lions

The early environment is known to commonly shape the entire life history of individuals. Whether it is the amount of resources provided by parents or the amount and complexity of social interactions, the effects are often lasting over a lifetime. Pups of Galápagos sea lions (Zalophus wollebaeki) born on the small island of Caamaño in the centre of the archipelago are no exception. Some parts of the island have a very low local population density and other parts have a very high one, thereby providing pups with either no, a few, or a lot of social interactions. Over the last couple of years, we have established personality tests that reveal personality dimensions in pups. We documented that hormones as important infochemicals correlate with personality and island exploration. We used time-depth recorders (TDRs) to unravel a foraging polymorphism in adults where some are choosing to forage on the sea floor (benthic foragers), some are pelagic foragers and some are almost exclusively foraging at night. These foraging niches are related to hormonal differences and in turn are related to fitness: when the ocean is warm, the benthic foragers enjoy a fitness benefit and when the ocean is cold, both the pelagic and night-time foragers enjoy a fitness benefit.

We propose to link the early environment to later foraging tactics and the individual life histories and hypothesise:

1. The early social environment is associated with personality and hormonal differences in pups and leads to variation in the onset and amount of exploration of the island and will affect the ontogeny of diving behaviour: social niches influence later niche choice and niche conformance.
2. The variation in the behavioural and hormonal phenotype of young sea lions will affect their choice of foraging strategy (benthic versus pelagic versus night-time pelagic) as subadults and adults, creating a foraging niche polymorphism with individual variation within the polymorphism.
3. The foraging niche polymorphism affects the fitness of sea lions in a dynamic interaction with the variable environment: warm sea surface temperature favours benthic foraging, whereas cold sea surface temperature favours pelagic foraging.

This project will combine the detailed investigation of the early social niche of pups, their personality and hormonal variation with the equally detailed investigation of the ontogeny of foraging niches, how individualised foraging niches are chosen by sea lions and what the ensuing fitness consequences are.