Climate change not only affects mean temperature and precipitation but also enhances temporal fluctuations in these conditions. Relatively little is known about the response of species to climate change: some studies show that species can track shifting onsets of seasons through phenotypic plasticity and/or micro-evolution, while others emphasize the limits of species responses. Even less is known about how species respond to changes in climate fluctuations: how climate fluctuations affect vital rates (i.e. survival, growth and reproduction of individuals), population fluctuations and hence extinction risks. We propose that adaptation to past climate fluctuations is an indicator of whether organisms can cope with future climate fluctuations. Two mechanisms have been suggested by which populations may buffer environmental variation: 1) well-known life history trade-offs at the individual level (e.g. resources invested in reproduction are not available for growth) resulting in negative covariance among vital rates, and 2) reduction of variation in those vital rates to which population growth is most sensitive.

Results/Conclusions

We show with demographic data for 40 plant species and simulations in which vital rates were randomized that these hypotheses are not supported by data. In contrast, positive covariances between reproduction and survival rates predominate: poor years are really poor, while good years are really good. Our results suggest that plant populations have not evolved to buffer the effects of environmental fluctuations on their growth rates. Increasing climate variability is therefore expected to increase population fluctuations and extinction risks and will affect especially short-lived species that contribute much to biodiversity.