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1961). Similar species from watersheds devoid of major migration barriers may exploit a greater degree of stream connectivity and increased gene flow between species members. Thus, species located below major migration barriers are known to have a higher frequency of genetic heterogeneity than the same species located above the barrier (Echelle et al. 1976). This suggests that the displacement of native species by congeneric endemics could occur due to greater genetic diversity-or plasticity- (Hocutt and Hambrick 1973) when transported across migratory barriers. The introduction of species into areas where congeneric natives are present can be especially deteriorative to the native species (Hocutt and Hambrick 1973, Hlohowskyj and White 1983, Ross 1986, Winston et al. 1991, Mack et al. 2000, Walser et al. 2000, Perry et al. 2002). Niche partitioning and competitive interactions have been shown to be rather complex within assemblages possessing multiple congeneric species (Paine et al. 1982). It is safe to assume that introductions to such environments would further complicate, and possibly interrupt, ecological processes already in place. The replacement of two cyprinid species above a Red River impoundment depicts a common pattern. The superseding species were morphologically, chromatically, and ecologically similar (Winston et al. 1991). Strong evidence links decreased ecological separation between species with increased taxonomic distance (Ross 1986). Competition between closely related species is probable due to the lack of evolutionary divergence and similar habitat specialization (Hlohowskyj and White 1983). Congeneric species tend to be very cross compatible, which raises concerns relating to the effects of heterospecific reproductive interactions (Mooney and Cleland 2001). 13
Hybridization with introduced species is often given little attention but can be very detrimental to cross compatible species in the host watershed (Harper et al. 1961, Courtenay and Hensley 1980, Perry et al. 2002). Native species can experience reduced fitness and a high chance of extinction due to the effects of hybridization with nonnative species (Dowling et al. 1989). Genetic introgression can lead to functional extinctions, reducing population numbers and genetic integrity to the point where a species plays no practical role in ecosystem processes (Harper et al. 1961, Mooney and Cleland 2001, Perry et al. 2002). Similar species with similar habitat preferences and spawning habitats will have a high probability of hybridization (Mayden and Burr 1980). Nest associated broadcast spawning is a reproductive characteristic of many shiner species (Schwartz 1972). Close proximity reproduction and temporal overlap in reproductive trials suggest a high likelihood of hybridization (Mayhew 1983, Menzel 1978). Studies have revealed that the effects of introgression may be greater in one species than the other (Dowling et al. 1989, Eisenhour 1995). This seems to be especially true with rare species. The potential for hybridization and introgression may be increased due to the difficulty a species encounters in finding mates of their own species (Mayhew 1983, Dowling et al. 1989). Literature citing evidence of hybridization in shiner species include: Menzel (1978), Burkhead (1983), Mayhew (1983), Dowling and Moore (1985), and Dowling et al. (1989). In fact, the hybridizing capacity of shiner species has been documented as being truly extensive (Schwartz 1972). Invasive species populations can begin with a small number of individuals (Simberloff 1986). However, a larger founder population will increase the probability of establishment (Williamson and Fitter 1996). If small, introduced populations are to 14
Page 1 and 2: An Experimental Study of Vertical H
Page 3 and 4: Acknowledgements I would like to th
Page 5 and 6: LIST OF TABLES Table 1. Results of
Page 7 and 8: In order for similar species to avo
Page 9 and 10: species diversity should increase (
Page 11 and 12: noting that the abundance of some s
Page 13 and 14: exhibited by species involved; the
Page 15 and 16: new environment (Dueser and Porter
Page 17: host environment, proposing that a
Page 21 and 22: alteration may reduce the habitat s
Page 23 and 24: in the upper Greenbrier River and o
Page 25 and 26: ubiquitous, appearing in all channe
Page 27 and 28: Literature Cited Addair, J. 1944. T
Page 29 and 30: Gibbs, R. H. 1957. Cyprinid fishes
Page 31 and 32: Lobb, M. D., III. 1986. Habitat use
Page 33 and 34: Paybins, K. S., T. Messinger, J. H.
Page 35 and 36: Chapter 2: An Experimental Study of
Page 37 and 38: Introduction Non-native fishes nega
Page 39 and 40: native cyprinids on their native co
Page 41 and 42: enthic, near-benthic, lower-pelagic
Page 43 and 44: N. telescopus had modes in the lowe
Page 45 and 46: native species pairs were partially
Page 47 and 48: interspecific separation of vertica
Page 49 and 50: MacArthur, R. and R. Levins. 1967.
Page 51 and 52: Table 1. Results of Chi square Test
Page 53 and 54: Total Number of Occurrences 160 140
Page 55: Total Number of Occurrences 160 140

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