Climate change, body size, and phenotype dependent dispersal.

Gardner and colleagues [1] recently reviewed the evidence for shifts in body size as a third major response to climate change, in addition to widely recognized shifts in the ranges and phenology of species [2]. The authors conclude that, although a pattern of declining body size is commonly observed (i.e. [3]), increases in body size might also occur and more detailed studies are needed [1]. Although their review focuses on the evidence for declining body size as a third general response to climate change, we would like to add that the effect of climate on individual body size has the potential to impact one of the other major responses to climate change dramatically: species’ range shifts (Figure 1). Although rarely made explicit, much of the literature makes the implicit assumption that dispersal will facilitate species’ range shifts into areas with newly suitable climatic conditions [2,4,5]. However, there is accumulating evidence indicating that dispersal behavior is often phenotype dependent and that body size is a major factor shaping the propensity and ability of individuals to disperse [4,6,7]. Body size is also likely to play an important role in establishment once those individuals that move beyond the prior range borders arrive in new habitats. Incorporating the interactive effects of body size and dispersal will allow a more thorough understanding of the effects of climate change on range shifts, and will improve the ability to predict the effects of climate change on biota. Although under some conditions the influence of climate change on body size might facilitate species’ range shifts, the emerging consensus that warmer climates will result in generally smaller body sizes [1,3] suggests that this effect will often be inhibitory for many species. In either case, effects of climate on body size and dispersal should be incorporated into analyses assessing range shifts and into planning associated with maintaining the capacity of populations to make such range shifts. To date, there are relatively few examples of direct connections between climate change and dispersal behavior, and observed patterns have been mixed (i.e. [8,9] and references therein). Further studies incorporating explicit linkages between climate, body size and dispersal might provide insight into examples in which species either have not shifted their ranges in response to climate change or have shown unexpected shifts (e.g. examples in [10]). Long-distance dispersers (the ‘tail’ of the dispersal kernel) are critical in driving range shifts that are rapid