Résumé
Many species facing climate change have complex life cycles, with
individuals in different stages differing in their sensitivity to a
changing climate and their contribution to population growth. We use a
quantitative genetics model to predict the dynamics of adaptation in a
stage-structured population confronted with a steadily changing
environment. Our model assumes that different optimal phenotypic values
maximize different fitness components, consistent with many empirical
observations. In a constant environment, the population evolves towards an
equilibrium phenotype, which represents the best compromise given the
trade-off between vital rates. In a changing environment however, the mean
phenotype in the population will lag behind this optimal compromise. We
show that this lag may result in a shift along the trade-off between vital
rates, with negative consequences for some fitness components, but, less
intuitively, improvements in some others. Complex eco-evolutionary
dynamics can emerge in our model due to feedbacks between population
demography and adaptation. Because of such feedbacks loops, selection may
favor further shifts in life history in the same direction as caused by
maladaptive lags. These shifts in life history could be wrongly
interpreted as adaptations to the new environment, while they only reflect
the inability of the population to adapt fast enough.