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Ecological Dynamics on Yellowstone’s Northern Range
centered on a geological mantle plume, or hotspot, where the molten magma comes close to the surface (Anders et al. 1989, Pierce and Morgan 1992, Pritchard 1999). The North American plate is thought to have moved to the southwest, leaving a series of volcanic traces from southwestern Idaho along the Snake River to the currently active Yellowstone region. Geomorphological changes have not stopped, for uplifting is continuing (Reilinger 1985). YNP is characterized by boiling mud pots, thermal pools, geysers, a volcanic caldera, ancient lava flows, and eroding rivers and waterfalls, which were the original reason for its protection as a park—wildlife and other life forms were an afterthought. Geomorphological changes may proceed gradually or may occur abruptly. Yellowstone witnessed a major earthquake as recently as 1959, whereas the Grand Canyon of Yellowstone is a prime example of wearing away by water on a grand scale.
Over the last 70 million years, climates have changed virtually continuously (Miller et al. 1987). The Pleistocene saw at least four major changes in climate due to alternating glacial and interglacial periods, although there may have been many important events on a shorter time scale. Over the last one million years, the earth oscillated between 90,000-year-long cold periods with ice accumulation and 10,000-year-long warm periods of ice melting (Muller and MacDonald 1997, Petit et al. 1999).
Pleistocene environments shaped the current Yellowstone landscape, flora, and fauna. Changes in the distribution of plants and animals and extinction of species were prevalent. Horses, camels, mammoths, and many other large mammals became extinct, whereas caribou, lemmings, musk ox, and other mammals retreated to the north at the end of the Wisconsin glaciation about 10,000 years before present (YBP). In addition, the abiotic changes must have caused adaptive responses—through both genetic evolution and behavioral or other plastic responses—in Yellowstone’s biota. However, information to evaluate these changes is sparse or completely lacking.
PALEOBIOLOGY OF THE GREATER YELLOWSTONE AREA
A paleobiological perspective is useful in identifying prehistoric processes that have shaped the Greater Yellowstone ecosystem (GYE), determining whether they continue to operate, and describing reasonable boundaries that may be placed on future variation.