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Show Anthropogenic changes in biogeography Donald W. Sada and James E. Deacon ABSTRACT The Great Basin, the most arid region in North America, has small widely spaced aquatic habitats relative to those in more mesic regions. They range from small rivers and streams to large lakes and small thermal and cold springs, all of which terminate either on playas or in valley- fill alluvium. Springs in the region are typically isolated. Great Basin wetlands generally support taxa that are widespread throughout North America. However, the regional endemic fish fauna documented and described so well by Carl Hubbs and Robert Miller is now complimented by numerous more recently described endemic insects, amphibians, and mollusks. Presence of this fauna demonstrates that size of Great Basin wetlands is not indicative of their biological importance. Comparison of historical and current records shows that anthropogenic activities have modified structure of Great Basin aquatic communities. Forty- six fish species ( 50 subspecies) have been introduced by the public and fishery management agencies and 15 endemic forms ( 11 fish, three mollusks, and one insect) have become extinct since the early 1900s. Twenty- four Great Basin aquatic species ( limited to only fish and one insect) are listed as threatened or endangered by the U. S. Fish and Wildlife Service. Extinctions and status declines have typically been reported as discrete occurrences affecting individual taxa ortaxa occupying localized habitats. In this paper we attempt to identify causal relationships by examining the temporal patterns of decline exhibited by endemic aquatic taxa of the Great Basin. This analysis shows temporal a relationship between decline and extinction and suggests some predictability in the rate of decline expected for the future. It also |