Abstract
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 maximize resource acquisition should be under selection. Here, using foraging trip duration data collected over 7years on black-browed albatrosses (Thalassarche melanophris) on the Kerguelen Islands in the southern Indian Ocean, we examined 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 (ENSO). Using double hierarchical models, we found no evidence that individuals change their mean foraging trip duration in response to a changing environment, but found 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 self-maintenance trips. We found weak correlations between sea surface temperature and the ENSO, 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.
Highlights
A major challenge in contemporary ecology is to understand how environmental change impacts individuals, populations and species
We examine the effect of El Niño Southern Oscillation (ENSO), a global climate phenomenon known to be an important driver of ecosystem-wide changes in the Southern Ocean, on the foraging behaviour of black- browed albatrosses
Our results show that ENSO has a strong impact on the variability in foraging trip duration, with little to no effect on the mean trip duration
Summary
A major challenge in contemporary ecology is to understand how environmental change impacts individuals, populations and species. While variability in foraging behaviours are likely to be an important mechanism through which individuals mediate the effects of changing prey distributions, studies looking at this are much rarer This is despite being acknowledged as an important source of ecological variation (Houslay et al, 2019; e.g. Hückstädt et al, 2012; Montiglio et al, 2015) with a heritable component (Martin et al, 2017; Prentice et al, 2020). Seabirds are an ideal bioindicator for such research as the wealth of biologging data can be used to model within- and between-individual changes over time, through repeated measures within and between years Coupling these data with long- term measures of reproductive success on individual birds is crucial to assessing how selection acts on variability. This yielded 167 birds (94 tracked individuals and 73 partners of known identity), where we had an estimate of foraging trip duration, breeding success, age and sex
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