The silver carp and bighead carp (Cyprinidae), native to eastern Asia, have been introduced into the United States in attempts to improve water quality in aquaculture ponds, reservoirs, and sewage pools. Escaped or released specimens from fish farms have been reported in many states, and both species are already locally established and spreading further. We used the Genetic Algorithm for Rule-set Prediction (GARP) to model the niches of these two carps in their native ranges using hydrologic and general environmental parameters in concert with native distributional data. The results accurately predicted native occurrence data withheld from the modeling process (P < 0.01). We then projected the niche models onto the North American landscape. Native niche range models significantly predicted known occurrence data from North American introductions (P < 0.001). Further, the models suggest that both species have the potential of spreading throughout the eastern U.S. and selected areas of the West Coast.
Unequivocal Eocene suckers from China are for the first time reported here. This discovery demonstrates that catostomids of the Eocene Epoch (some 55 35 Ma ago) are scattered widely on mainland Asia as well as western North America. The present day disjunct distribution pattern of catostomids, with 68 extant species widespread in North America and the northern part of Middle America and only two in the restricted areas of Asia, is the result of their post-Eocene decline in Asia due to the competitive pressure from cyprinids, their Late Cenozoic radiation in North America, and the vicariant and dispersal events triggered by the changed biogeographic landscape. All of these prove to be a historical product of the geological, biological, and climatic changes throughout the Cenozoic.Keywords: China, catostomids, Eocene, biogeography.Suckers (Catostomidae) are now one type of the most widespread freshwater fishes in North America, with a southern extension into Mexico and Guatemala. Among the family's 69 extant species [1,2] , only two occur elsewhere: one in northeastern corner of Siberia and the other in the Yangtse River and Minjiang River (Fujian Province), China [3,4] . This disjunct distribution ( fig. 1(a)) has long puzzled ichthyologists and biogeographers alike. Although Darlington's [5] scenario of eastern Asian origin of catostomids and their subsequent dispersal routes gained acceptance [6 8] , it is currently considered problematic because it lacked a robust phylogenetic analysis and an adequate fossil record. Surprisingly, with an almost blank record of fossil suckers in east Asia but quite a few from the then so-called "Oligocene" and "Miocene" in North America [9 11] , Darlington [5] postulated that "catostomids originated in eastern Asia, moved primarily from Asia to North throughout western North America [12,13] ( fig. 1(b)). They were all referred to the genus †Amyzon [15 18] ( fig. 2(b)), though the monophyly of the genus [17] and the validity of some included species [19] were questioned. Suckers belonging to modern genera did not appear until the middle or lateMiocene (approximately 15 Ma ago); once they did, they occurred on both sides of the Continental Divide of North America [13,20,21] ( fig. 1(b)).Prior to this report, fossil suckers were conspicuously absent from China except a few disarticulated operculars and vertebrae assigned as Catostomus sp. from the middle Eocene of Inner Mongolia, China [1,22] . In fact, the fossil record of suckers from Asia as a whole was sketchy. Sytchevskaya [7] described a late Eocene or early Oligocene sucker, †Vasnetzovia, from the Far East coastal area of Russia but did not mention its pharyngeal teeth. Other fossil suckers described by the same author from the early-middle Eocene and early Oligocene of Zaysan Basin, East Kazakhstan, were based on detached pharyngeal teeth alone. Among her findings, all but an ictiobine, †Vasnetzovia, were dismissed by Smith [1] . Besides, their occurrences were restricted to northern Asia [7] . Systematic...
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