A Tipping Point: Using the Past to Forecast Our Future
Earth’s environments are rapidly changing. Yet, animals evolved in the face of environmental change. Extracting the responses of animals to perturbations of the past is one of the best ways of unraveling how they will respond to perturbations of the future. Large environmental events provide unique opportunities for insights into resilience of animals over time. The transition from the cold, arid Late Pleistocene (LP) glacial period to the warm, mesic Holocene interglacial witnessed the extinction of two-thirds of all the large-bodied mammalian genera (ground sloths, short-faced bears, giant wombats, etc.) and global expansion of modern humans. The smaller mammalian survivors of the extinction (voles, gophers, ground squirrels, etc.) persisted but showed range changes, species turnover, and diversity decline. Subsequent but smaller climatic events, such as the Medieval Warm Period, continued to exert impacts on animals by causing adjustments in population abundances, body size and changes in genetic diversity. This retrospective view yields predictions for Earth’s animals of the future. We will certainly lose many species, while a few will thrive. Other species will abandon their former homes and occupy new areas. Surviving animals may decrease in size and otherwise change in appearance, behavior and/or genetic diversity. Although past climates exerted evolutionary pressures on animals, the rate and magnitude of changes in the next century suggest perturbations too fast for present species to keep pace with, resulting in a world very different than it has been for millions of years. Yet in addition to climatic changes, our planet faces the added pressure of 7+ billion people and all the resources we require to sustain ourselves. No place in the biosphere is now removed from humanity’s impact. Charting the future of biodiversity requires not only a historic perspective, which details the timing, scale, and magnitude of past global state shifts, but also now must be combined with complex systems theory to forecast the uncertainty of our planet’s future.