Albatrosses respond adaptively to climate variability by changing variance in a foraging trait
Résumé
The ability of individuals and populations to adapt to a changing climate is a key determinant of
population dynamics. While changes in mean behaviour are well studied, changes in trait variance
have been largely ignored, despite being assumed to be crucial for adapting to a changing
environment. As the ability to acquire resources is essential to both reproduction and survival,
changes in behaviours that maximise resource acquisition, should be under selection. Here, using
foraging trip duration data collected over 7 years on black-browed albatrosses (Thalassarche
melanophris) on the Kerguelen Islands in the southern Indian Ocean, we examine the importance
of changes in the mean and variance in foraging behaviour, and the associated effects on fitness, in
response to the El Niño Southern Oscillation. Using double hierarchical models, we find no
evidence that individuals change their mean foraging trip duration in response to a changing
environment, but strong evidence of changes in variance. Younger birds showed greater variability
in foraging trip duration in poor conditions as did birds with higher fitness. However, during
brooding, birds showed greater variability in foraging behaviour under good conditions,
suggesting that optimal conditions allow the alteration between chick provisioning and selfmaintenance
trips. We found weak correlations between sea-surface temperature and the El Niño
Southern Oscillation, but stronger links with sea-level pressure. We suggest that variability in
behavioural traits affecting resource acquisition is under selection and offers a mechanism by
which individuals can adapt to a changing climate. Studies which look only at effects on mean
behaviour may underestimate the effects of climate change and fail to consider variance in traits as
a key evolutionary force.