Climate change and dispersal
Adaptation to climate change can work at different scales. Individuals may respond flexibly to local changes in ecology and thereby adjust their phenotypes to the changing circumstances. If this is not possible, they may search for another place to breed, where the environmental circumstances fit their phenotype better. Dispersal as process in adjustment of organisms to climate change has not been studied a lot, partly because it is difficult to track individuals while they move to an alternative site.
Long-distance migrants increasingly arrive too late at their breeding grounds, to profit optimally from the short burst of insects available to feed their offspring. They may have difficulties anticipating the advances in spring, as they have limited flexibility while migrating from their distant wintering grounds. A rather easy solution could be to continue migration to the north, until a habitat is reached where the phenology of major prey fits the phenology of the bird. In this way, individual restore the match with the environmental phenology, but may also allow new evolutionary directions if they bring new genotypes on which selection can act.
Dispersal as a way to adapt seems so easy, that it is difficult to understand that many populations seem to have become mismatched with the phenology of their food supply. One reason could be that costs of dispersing to a distant breeding sites may be high: it may be difficult finding a suitable place, and selection pressure may operate there to which the individual is not adapted (local disease strains?). The individual may thus be better adapted to the single timing trait, but got maladapted for other traits that are important in this environment.
Evaluating the importance of dispersal as adaptation to climate change requires estimates of its occurrence and the associated costs and benefits. Using ring-recapture data we could show that pied flycatchers regularly disperse large distances between birth areas in the UK and breeding in the Netherlands1. Whether this happens more in warmer years, and whether especially late individual disperse to the north is yet unknown, but we aim to find out using stable isotope ratios of flycatcher feathers.
The fitness consequences of long-distance dispersal are ideally studied by experimentally translocating individuals to the north and measure their performance. We managed to do so in pied flycatchers. They were caught in The Netherlands, and brought overnight to southern Sweden, where spring phenology is two weeks later. In a warm spring, we expected these birds to be better timed with the local food peak, and possibly have raised more offspring if local adaptation was relatively unimportant. Although we managed to have the birds breeding here, and they also bred considerably earlier than the Swedish birds, we could not demonstrate an advantage. This was likely caused by the experimental year being exceptionally cold, and/or because these birds were locally maladapted2. We hope to continue these experiments in the near future.
- Claudia Burger
- Both C. et al (2012), J. Avian Biol. 43:193-197, doi:10.1111/j.1600-048X.2012.05721.x
- Burger C et al (2011), Plos One 8:e83176, doi:10.1371/journal.pone.0083176
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