Pleistocene Megafauna in Beringia (U.S. National Park Service)

Figure 4. The probability density graph shows that the total numbers of animals in northern Alaska varied widely over time. The small pie charts show the relative abundances of the five main herbivore species over time. Data from Mann et al. 2015.

Why Did the Megafauna Live There?

Modern Beringia is covered by vast expanses of permafrost, peat, spongy tundra vegetation, and boreal forests of mostly coniferous trees. Much of it is buried in snow over half the year and during the cool, wet summer, it swarms with mosquitoes. This modern ecosystem supports a fraction of the animals that lived there during the Pleistocene. So, what was different? Not surprisingly, the climate was generally colder and drier during most of the Pleistocene, which would seem to make it less hospitable to megafauna. Because sea level was so much lower, the land mass of Beringia was larger and included the expansive Bering Land Bridge. This resulted in a more continental climate with little precipitation and clear skies: conditions that produced a unique biome called the Mammoth Steppe (Guthrie 1990), unlike anything found in Beringia now. The climate was too cold for trees and the dry conditions favored steppe-like grasslands, which provided abundant food for grazing megafauna; the late-Pleistocene megafauna were grazers and not browsers (or wood-eaters). The dry grasslands and low snow levels also provided a firm substrate that was easy for the hooved animals to walk over throughout the year.

The Mammoth Steppe was a complex biome that changed over time and across the region. This resulted in a mosaic-like ecosystem that varied in response to a constantly changing climate. During the Pleistocene, the climate changed much more dramatically than it has during the last 10,000 years, the period known as the Holocene, a remarkably stable climatic period compared to the preceding million years or so. The unstable climate of the Pleistocene caused rapid changes in the plant communities and thus forage for megafaunal herbivores. Abundance and distributions of these animals would have varied in response to the changes. Being large, the megafauna would have been able to move across the landscape tracking favorable patches of habitat both seasonally and over longer time scales.

Because of low snow levels and clear weather, green-up would have been earlier than now so the Mammoth Steppe growing season was probably longer. The clear skies of a continental climate may have allowed warmer temperatures during the growing season than occur with modern cloudier weather (Guthrie 2001). Mammoth Steppe soils were therefore dryer, warmer, and more fertile than now (Young 1982, Walker et al. 2001). This would have enhanced plant productivity and megafauna, that could graze around the clock, and could grow larger during the summer. With the nutritious plant growth, the megafauna also would have been able to consume enough in the summer to put on reserves to help them survive the long, cold winter.

This was a complete ecosystem of megafauna with herbivores and the predators that consumed them. Like most ecosystems, there were many more herbivores than carnivores. The giant short-faced bears may have mostly scavenged already-dead herbivores (Matheus 1995), but brown bears, lions, and wolves undoubtedly hunted and killed their prey. Radiocarbon dates suggest the lions may have specialized in hunting horses (Mann et al. 2013).