EVOLUTIONARY RESPONSES TO CHANGING CLIMATE

TLDR

Quaternary paleoecology has traditionally viewed evolution as slow relative to climate change, so biotic responses were thought to be persistence, range shifts, or extinction, but models now show that the speed of adaptation can influence invasion, migration, extinction risk, and vegetation productivity. The authors contend that these outcomes all involve evolutionary processes and propose that collaboration between paleoecologists and evolutionary biologists will refine paleorecord interpretations and improve predictions of biotic responses to future climate change. Recent models and experiments examine species tolerance limits, environmental gradients, and the interplay of demography, gene flow, mutation, and other genetic factors, while new techniques—such as resurrecting ancient populations from sediment and using high‑resolution macrofossil and DNA analyses—enable direct documentation of adaptation, range shifts, population size changes, and extinctions. Genetic differentiation is ubiquitous, with adaptive divergence arising on timescales comparable to climate change—decades for herbaceous plants and centuries to millennia for long‑lived trees—demonstrating that biologically significant evolutionary responses can accompany temporal climate change.

Abstract

Until now, Quaternary paleoecologists have regarded evolution as a slow process relative to climate change, predicting that the primary biotic response to changing climate is not adaptation, but instead (1) persistence in situ if changing climate remains within the species' tolerance limits, (2) range shifts (migration) to regions where climate is currently within the species' tolerance limits, or (3) extinction. We argue here that all three of these outcomes involve evolutionary processes. Genetic differentiation within species is ubiquitous, commonly via adaptation of populations to differing environmental conditions. Detectable adaptive divergence evolves on a time scale comparable to change in climate, within decades for herbaceous plant species, and within centuries or millennia for longer-lived trees, implying that biologically significant evolutionary response can accompany temporal change in climate. Models and empirical studies suggest that the speed with which a population adapts to a changing environment affects invasion rate of new habitat and thus migration rate, population growth rate and thus probability of extinction, and growth and mortality of individual plants and thus productivity of regional vegetation. Recent models and experiments investigate the stability of species tolerance limits, the influence of environmental gradients on marginal populations, and the interplay of demography, gene flow, mutation rate, and other genetic processes on the rate of adaptation to changed environments. New techniques enable ecologists to document adaptation to changing conditions directly by resurrecting ancient populations from propagules buried in decades-old sediment. Improved taxonomic resolution from morphological studies of macrofossils and DNA recovered from pollen grains and macroremains provides additional information on range shifts, changes in population sizes, and extinctions. Collaboration between paleoecologists and evolutionary biologists can refine interpretations of paleorecords, and improve predictions of biotic response to anticipated climate change.