Résumé
Understanding the mechanisms that produce novel ecosystems is of joint
interest to conservation biologists and paleoecologists. Here, we define
and differentiate transient from accumulated novelty and evaluate four
climatic mechanisms proposed to cause species to reshuffle into novel
assemblages: high climatic novelty, high spatial rates of change
(displacement), high variance among displacement rates for individual
climate variables, and divergence among displacement vector bearings. We
use climate simulations to quantify climate novelty, displacement, and
divergence across Europe and eastern North America (ENA) from the last
glacial maximum (LGM) to present and fossil pollen records to quantify
vegetation novelty. Transient climate novelty is consistently the
strongest predictor of transient vegetation novelty, while displacement
rates (mean and variance) are equally important in Europe. However,
transient vegetation novelty is lower in Europe and its relationship to
climatic predictors is the opposite of expectation. For both continents,
accumulated novelty is greater than transient novelty, and climate novelty
is the strongest predictor of accumulated ecological novelty. These
results suggest that controls on novel ecosystems vary with timescale and
among continents, and that the 21st-century emergence of novel ecosystems
will be driven by both rapid rates of climate change and the emergence of
novel climate states.