The late Quaternary megafaunal extinctions are a natural system for studying the patterns and mechanisms of species extinction. In North America, woolly mammoth (Mammuthus primigenius) went extinct between 13,800 and 10,000 BP, which is the time that climate and vegetation changed sharply and humans expanded into North America. Proposed hypotheses are nature-driven vs. humans-driven: nature-driven hypotheses include temperature changes and food resource loss, while human-driven hypothesis is explained as human overhunting. Here we simulate woolly mammoth potential distributions under climate and vegetation changes in North America after the Last Glacial Maximum (LGM), and test the hypothesized natural drivers of the extinction, by estimating energetic heat balance and vegetation carrying capacity for mammoths using a mechanistic physiological model (Niche Mapper) to simulate mammoth metabolic rate, dietary requirements, and freshwater requirements. Niche Mapper simulations are driven by climate dataset from the Community Climate System Model version 3 (CCSM3) TraCE-21ka simulations, vegetation simulations from the LPJ-GUESS dynamic vegetation model, and newly tabulated trait data for woolly mammoths. The resolutions are every 500 years and 0.5°x0.5° latitude/longitude in the perspectives of time and space.
Results/Conclusions
Primary results indicate that abrupt climate warming and ice sheets tightly constrained woolly mammoth distributions in most areas of North America around 14,000 BP, except in Alaska while grassland and graminoid tundra loss in 12,000 – 10,000 BP due to abrupt cooling and moisture level change contributed to the final extinction event (with two island refugia for mammoths survival till the middle Holocene). Glacial ice sheet limited woolly mammoth distributions into the higher latitudes except in Bering Land Bridge, while warmer temperature in lower latitudes limited mammoth distributions to the south. The abrupt climate warming around 14,000 BP decreased potential distributed habitats for woolly mammoth in the southern edge further, when the ice sheet still covered most areas in northern North America. Alaska supported woolly mammoth survival after 14,000 BP due to cool climate as suggested by previous proxies work, yet CCSM3 TraCE simulations did not suggest Alaska as a proper habitat for woolly mammoth because of simulated warmer temperature in the glaciation caused by upper air wave structure resulted by the ice sheets. The Niche Mapper simulations can help resolve the drivers of megafauna extinction, and reinforce the high vulnerability to extinction for megaherbivore population under climate change.