NEW YORK — Humans, not climate change, caused the extinction of large plant-eating animals, such as the mammoth, mastodon and ground sloth, 13,000 years ago in North America, researchers at Fordham University report in the August 2005 issue of Ecological Monographs.
Ecologists Guy Robinson, Ph.D., Lida Pigott Burney and David Burney, Ph.D., found evidence in the soil records of the bogs and ponds of southern New York State that indicates a dramatic decrease in the number of large animals approximately 1,000 years before a millennium-long cold period at the end of the last ice age. A period of climate change is commonly believed to have been responsible for their demise.
The Fordham team’s research indicates that the extinction of the large animals in North America occurred at the same time that humans emerged on the continent. According to Fordham researchers, humans overhunted the large animals, leading to their population collapse.
“Each lake and bog deposit that we examined told a similar story of a habitat absent the existence of any threatening factors, except for the introduction of humans to the ecosystem,” said Robinson. “Humans appear to be the fatal factor that brought about this prehistoric disaster.”
The researchers pinpointed the time of the large animals’ disappearance by monitoring the soil record for a spore that thrived on animals’ excrement. Soil records also show an increased frequency of widespread fires that were fueled by the excess foliage and vegetation no longer being eaten by the diminishing number of large animals. The increased frequency of landscape fires is a widely accepted scientific marker of the arrival of humans.
Researchers were able to mark dramatic shifts in environmental or climatic conditions of a region by searching for changes in the number of microscopic fossils, such as pollen, spores or other particles that are preserved in the soil record. The Fordham research team published similar research in Proceedings of the National Academy of Sciences in 2003 that connected the arrival of humans on the island of Madagascar with the extinction of flightless birds, giant lemurs and other large animals on the African island.