Forecasting the trajectories of species assemblages in response to
ongoing climate change requires quantifying the time lags in the
demographic and ecological processes through which climate impacts
species' abundances. Since experimental climate manipulations are
typically abrupt, the observed species responses may not match their
responses to gradual climate change. We addressed this problem by
transplanting alpine grassland turfs to lower elevations, recording
species' demographic responses to climate and competition, and using
these data to parameterize community dynamics models forced by scenarios
of gradual climate change. We found that shifts in community structure
following an abrupt climate manipulation were not simply accelerated
versions of shifts expected under gradual warming, especially when they
missed the rise of species benefiting from moderate warming. Time lags
in demography and species interactions controlled the pace and
trajectory of changing species' abundances under simulated 21st century
climate change, and thereby prevented immediate diversity loss.