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<br />OD2471 <br /> <br />Because biodiversity is a characteristic of natural ecosystems, it is not enhanced by the <br />introduction of nonnative sp.ecies. Biodiversity can be reduced by shifts in the natural <br />patterns of relative abundance (Temple 1990). There is no doubt that biodiversity is <br />declining on the planet and there may be serious and unanticipated consequences for <br />humans (Ehrlich and Ehrlich 1983, Wilson 1992, Ward 1995). <br /> <br />Extinction results in an irrevocable loss of biodiversity. Three sets of factors are <br />thought to contribute to extinction: biotic factors, isolation, and habitat alteration <br />(Frankel and Soule 1981). Most extinctions involve a combination of factors (Frankel <br />and Soule 1981, Soule 1983, Wilson 1992). Biotic factors such as predation and <br />competition from introduced species may reduce or alter the density, range, and habitat <br />use of a native species. While these alterations may not eliminate a robust and <br />widespread species, they are likely to cause its decline and make the native population <br />more susceptible to other factors such as habitat alteration or isolation, Population <br />decline results in small population size, and small populations are prone to problems <br />such as demographic stochasticity, genetic deterioration, social dysfunction, and <br />extrinsic forces (reviewed by Raup 1991). Extinction is more likely to occur in small <br />populations that have fallen below the size of minimum viability (MacArthur and Wilson <br />1967; Simberloff 1974,1986; Raup 1991). <br /> <br />The case for conservation becomes most urgent as the population size of a <br />species becomes very small. Random events such as a chemical spill that would have <br />a relatively minor impact on a large and widely distributed population, could have <br />catastrophic and perhaps permanent effects on a smaller, restricted population. In the <br />interest of preserving the species and maintaining biodiversity, extraordinary measures <br />may be required to prevent extinction. For species like the big river fishes of the UCRB <br />that are threatened by biotic factors, control of introduced species becomes imperative. <br />The task is not necessarily a simple one: control of introduced species has been called <br />the "nasty necessity [because of] misconceptions about the nature and magnitude of <br />the problem, fears of the negative public reactions...and intimidation by the inefficient <br />labor-intensive nature of current eradication technologies' (Temple 1990), <br /> <br />Easy or not, the control of introduced non natives that are threatening the big river <br />fishes of the UCRB has become a necessity, and control measures must be developed <br />using an objective and structured approach. This report has four main objectives: (1) to <br />assess the effects of nonnative fishes on aquatic communities from national and <br />regional perspectives, (2) to identify and discuss the effects of introduced nonnative <br />fishes on the endangered big river fishes of the mainstream Colorado River, (3) to <br />identify measures appropriate for reducing or preventing negative impacts of nonnative <br />fishes on the big river fishes, and (4) to provide a strategic plan for guiding measures <br />for controlling nonnative fishes in the UCRB. The goal of this plan is mitigation of these <br />biotic factors that could lead to the extinction of the native big river fishes. <br /> <br />3 <br />