Limitations on adaptation: Evolutionary response to climatic change?

Abstract

There is mounting evidence to show that human activities have already left their mark on global climate, and can be expected to cause much greater changes in the global climate this century (IPCC, 1990, 1995, 2001, 2007). Increasing concern has thus focused upon how species and ecosystems will respond to these changes (Huntley et al., 1997) and the likely consequences for global biodiversity (Lovejoy and Hannah, 2005). One easily detectable and early response is the adjustment of species' phenology – the timing of their annual cycle of activities – to changes in seasonal climate. Abundant evidence has already accumulated showing that numerous species have exhibited such phenological responses to the climatic changes of the past half century (Parmesan and Yohe, 2003). However, the extent to which these responses reflect adaptive genetic evolution, as opposed to phenotypic plasticity, is generally unknown. In an elegant study published recently, Franks et al. (2007) have demonstrated that a shift in flowering time of the naturalised annual plant Brassica rapa (turnip (UK), field mustard (USA)) in response to a regional multi-annual drought in southern California was an adaptive evolutionary response.