"[Our results] demonstrate clearly how important phenotypic plasticity – call it flexibility if you like – can be for responding to a rapidly changing environment," Ben Sheldon of the University of Oxford told environmentalresearchweb. "In some cases, species or populations can track quite rapid changes in their environment without any difficulty."
Sheldon stressed, however, that that doesn't mean that all populations will track rapid changes, or even that this population would if there were even more dramatic warming. "But it does at least suggest that studying the ability of individuals to adjust their behaviour in different environments might be a useful way to categorise populations as to the likelihood that they will be able to adjust easily," he said.
Sheldon and colleagues at the University of Oxford and University of Edinburgh, UK, and CNRS, France, looked at data from a population of great tits (Parus major) in Wytham Wood near Oxford over the past 47 years. The mean egg-laying date of the birds has advanced by about 14 days, with the change appearing to begin in the mid-1970s. The peak availability of winter moth larvae – a key food source for the birds – has also advanced by around 14 days.
"We have been aware for some time that the population has been breeding earlier and earlier, and that the change was related to the ongoing changes in the climate," said Sheldon. "We realised that because we had observations of individuals in multiple years we could work out the mechanism that was causing the population to change, and because we'd also been collecting data on the timing of the birds' main food source – caterpillars – over that time that we could ask whether the birds' change had been appropriate given how other parts of the system were responding."
In this work, individual females showed similar responses to changes in spring temperatures. That's in contrast to a Dutch study in which individual great tits changed their laying date by different amounts for a given spring temperature change. This Dutch population did not track its environment closely and its fitness has declined, whereas the UK population is thriving.
Now the team will investigate the differences between UK and Dutch birds, try to understand whether their UK great tit populations are invariant with respect to other forms of plasticity, and look at the importance of large-scale (regional) and small-scale (individual tree) differences in timing for the birds' behaviour.
The researchers reported their work in Science.