How foreign is the past?/Lyons et al. reply

Since Humboldt and Darwin, ecologists have puzzled over what determines community assembly and structure and how community structure may change with time. Human activity is one potential driver. Impacts of modern human societies on the environment and its biota are massive, with many forms of pollution, loss and fragmentation of habitats, and extensive introductions of exotic species changing many ecological and biogeographical patterns. Prehistoric societies might be expected to have had a much lower impact on their environment. However, Lyons and colleagues1 propose that biotic communities were so fragile that the limited settlements, agriculture, and associated activities 6,000 years ago in North America were sufficient to fundamentally change community-assembly rules.