生態学：マンモスステップは見事に構成された生息環境だった

The Mammoth Steppe, the environment in which mammoths lived among a distinct community of vegetation and wildlife, was a unique ecosystem unlike anything that exists today, research in Nature reveals. The study, which draws on extensive environmental DNA analyses, helps to explain how this ecosystem changed over the past 50,000 years, and sheds light on the timing and cause of megafaunal extinctions, including the demise of the iconic woolly mammoth.

There has been some debate about what the Arctic ecosystem was like during the heyday of the Mammoth Steppe, in the later stages of the Pleistocene epoch (around 50,000 years ago), with two prevailing theories. Some studies propose that it was an extensive grassland populated year-round by grazers, such as woolly mammoth and bison, whereas others suggest that it was a more diverse ecosystem, including steppe and tundra, and an accompanying mix of animal life that was regionally and temporally diverse.

To fully understand the make-up of the Mammoth Steppe, Eske Willerslev and colleagues studied samples of environmental DNA, belonging to ancient plants and animals, from 535 different Arctic sites that span the past 50,000 years. They also analysed the DNA of more than 1,500 contemporary Arctic plant species as reference sources. The Mammoth Steppe was somewhere in between the two prevailing theories, the researchers suggest. It was a cold, dry and regionally complex steppe, composed of grasses, sedges, flowering plants and shrubs.

Some animal species survived much later than had previously been thought, the study also reveals. There is evidence in mainland Siberia for the presence of the woolly mammoth 3,900 years ago, woolly rhinoceros at 9,800 years ago and bison 6,400 years ago. This finding implies that humans coexisted with these megafaunal species for tens of thousands of years, and that human hunting was not an important factor in their demise. Instead, extinction came when the last pockets of steppe–tundra vegetation gave way to peatland, as the climate became warmer and wetter.