VARIATION ACROSS SPACE DOES NOT PREDICT EVOLUTIONARY CHANGE THROUGH TIME

To predict biotic responses to future climate change, a common approach is to extrapolate species’ responses to current environmental conditions into the future. These projections often make two key implicit assumptions: (1) the species’ adaptive potential is similar across its geographical range and (2) environmental variability among contemporary populations is a relevant predictive tool when projecting forwards in time. Within- and among-population variation is a key index of a species’ adaptive potential, but ecological studies with both temporal and spatial variation spanning climatic upheaval are rare. Here, we study covariations between shell size and abundance, and between shell size and shape of 29,000 individuals of fossilised planktonic foraminifera in the ecologically similar species Globoconella puncticulata and Truncorotalia crassaformis over 600,000 years. Size and abundance covary tightly at the species level, the covariation between size and shape predicted evolutionary divergence through time, and among-population trait covariances followed biogeographical expectations inferred from the species’ ecological optima. However, within-population temporal dynamics had negligible predictive power for the among-population spatial changes. We argue that spatial variation is a poor predictor of evolutionary change through time because dynamics of local sites cue on different combinations of environmental parameters. Therefore, future studies should incorporate the multifaceted nature of climate change to model species’ responses to their environment.