We are moving to a state of the earth system likely to lack any close analog in human history. Already, many communities have been transformed by human action and the legacies of past actions, and now comprise mixtures of species with no historical or evolutionary counterpart. In our efforts to predict, understand, and prepare for the behavior of ecosystems in a strange new world, geological and historical data are essential sources of information about processes governing species and ecosystems for time scales and states of the earth system that are inaccessible to direct observation. In particular, the glacial-interglacial cycles of the Quaternary, with their widespread reshuffling of species into communities with no modern analog, offer rich research opportunities for studying the abiotic and biotic processes governing the assembly and disassembly of communities.
Key questions include: How do we define novelty and by what criteria? How novel are current and projected climates, communities, and disturbance regimes relative to paleohistorical counterparts? By what mechanisms do novel climates give rise to novel ecosystems, and what metrics best represent the exposure of communities to climate-driven reorganization? When and where have novel ecosystems arisen in the past, and under what environmental conditions? How accurate are ecological forecasting models under novel climates, and where are the limits to predictability? These questions will be addressed by this talk and others in this organized oral symposium.
Results/Conclusions
Multiple definitions of novel ecosystems and climates exist. Here we define novelty as the degree of dissimilarity of a system, measured in one or more dimensions relative to a reference baseline, usually defined as either the present or recent historic time window. By this standard, novel communities have already begun to emerge, caused by land use and the intermixing of exotic and native species. Climatic mechanisms for triggering the reshuffling of species into novel communities include the emergence of previously unavailable portions of climate space (climate novelty), rapid climate changes combined with interspecific differences in rate of response (rate of displacement and disequilibrium), and the differential spatial trajectories of climate variables (divergence). Climate metrics representing these different mechanisms highlight different regions of the world as being at higher risk of community reshuffling, providing testable hypotheses for future study. Many projected climates by 2100AD lack close analogs in any modeled climates of the last 125,000 years, suggesting that end-century climates are novel relative to both current and previous interglacials.