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Grand Teton National Park Report

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Our National Parks house some of North America's most undisturbed habitat and offer a benchmark for comparing ecosystem dynamics with areas more influenced by human related perturbations. Dam construction has altered water flow patterns on many of our country's rivers resulting in species composition changes of aquatic plants, invertebrates and fish. Semi-aquatic mammals such as otters and beaver are also profoundly influenced by the irregular seasonal flow patterns resulting from reservoir release schedules. For example, Jackson Lake dam was constructed in 1910 resulting in the impoundment of an additional 625,000 cubic feet of water. Since its construction and the establishment of Grand Teton National Park (GTNP), this water has been released during mid- to late summer months causing unpredictable fluctuations of river levels after the normal spring run off. This unpredictability is illustrated by the trend in water flow on the Snake River at Moran for the period 1904-2000 (Figure 1). A species that has received little attention in terms of population numbers and resistance to abnormal water fluctuations resulting from Jackson Dam is the beaver (Castor canadensis). In GTNP, only the work of Collins (1976) has provided any significant knowledge of the distribution and habitat of the beaver in the Park. In fact, the beaver has been generally overlooked in the Greater Yellowstone Area with only a few studies conducted in Yellowstone (Warren, 1926; Jonas, 1955; Consolo-Murphy and Hanson, 1993 ).