Lythrurus

Abstract: Despite use of several character sets, phylogenetic relationships among species groups of the cyprinid genus Luxilus remain unresolved. To address this problem, cytochrome b was sequenced from representatives of each taxonomic unit within the genus and from several outgroups. When all outgroups were included, distance and parsimony analyses identified a single topology: (((L. cerasinus, L. zonatus group) L. cornutus group) L. coccogenis group). However, this topology was not appreciably better than alternative hypotheses from different character sets, and monophyly of the genus was not well supported. Saturation effects associated with contrasts involving the outgroup Cyprinella may have impacted resolution. When only Lythrurus was used as the outgroup, the same topology was recovered, and, except for the placement of L. cerasinus, relationships were well supported. General concordance of these results with those based on morphological characters provides support for a close relationship of the cornutus and zonatus groups and for basal position of the coccogenis group.

Abstract: Species distributional boundaries are often restricted even when there are no geographical barriers to limit expansion. Parapatry refers to a specific pattern of distribution in which two taxa have nonoverlapping distributions that meet along a common boundary (Smith, 1955). Determining what limits a species spread across such boundaries is challenging. Numerous examples of parapatry have been described for a wide variety of taxa and geographic regions. Both biotic and abiotic factors have been im-

Abstract: Foods, feeding periodicity and microhabitat use are reported for coexisting Notropis albeolus, N. ardens and N. cerasinus in the upper Roanoke River drainage, Virginia. All three species primarily occupied pool habitats, ate aquatic insect larvae or terrestrial adult insects, and were diurnal feeders. Notropis ardens (subgenus Lythrurus) was ecologically segregated from N. albeolus and N. cerasinus (both subgenus Luxilus) in vertical spacing in the water column and in taxa of foods used. The two Luxilus species were ecologically more similar, segregated only by vertical differences in microhabitat. Overlaps in resource use among the three species pairs suggested congruence of phylogenetic and ecological similarities. INTRODUCTION The phenomenon of resource partitioning is well-documented in reptile, bird and mammal communities (cf., Pianka, 1973; Schoener, 1974), and in numerous freshwater fish communities closely related, coexisting species differ ecologically, e.g., in microhabitat, food or feeding chronology (Hartley, 1948; Keast, 1965, 1966, 1978; Zaret and Rand, 1971; Werner and Hall, 1976, 1979; Werner et al., 1977). It has often been assumed that some segregation in resource use is a requisite for coexistence of species, and that observed ecological differences among coexisting taxa result from past or present competitive interactions. However, uncritical acceptance of a competition model to account for ecological differences among coexisting fish species may be unwarranted (Sale, 1979), and the plausibility of alternative hypotheses should be considered. Mendelson (1975), for example, suggested that coexisting minnows used resources in patterns set by morphological preadaptation. In eastern North America, minnows of the genus Notropis (Cyprinidae) often occur in multispecies aggregations, using habitats and foods that superficially appear similar. However, Starrett (1950), Whitaker (1977), Gillen and Hart (1980) and Hoover (1981) showed trophic segregation among coexisting Notropis species, and Moyle (1973) and Baker and Ross (1981) demonstrated that coexisting Notropis species segregated vertically into different microhabits. Mendelson (1975) showed that four coexisting Notropis were ecologically segregated more by use of space than by diet. While these studies suggest the importance of dietary and microhabitat segregation among coexisting Notropis, there has been too little comparative research within this diverse genus (at least 119 species) to permit generalization about mechanisms that facilitate species coexistence. In this study we evaluate ecological segregation among three syntopic Notropis species, with emphasis on microhabitat, food and feeding chronology in a complex upland stream system. We also provide information on cold vs. warm weather ecology of the species. Our study focuses on Notropis albeolus (white shiner, subgenus Luxilus), N. ardens (rosefin shiner, subgenus Lythrurus) and N. cerasinus (crescent shiner, subgenus Luxilus), which are the three most common Notropis in the upper Roanoke River drainage above Salem, Virginia (Jordan, 1889; Cairns et al. 1971; Jenkins, 1979). All three coexist in the river mainstream and in larger tributaries, but N. cerasinus occurs somewhat further 'Address reprint requests to Matthews.

Abstract: Historical and contemporary fish collection data were used to compare the relative abundance of introduced rough shiner (Notropis baileyi) in the Chattahoochee River (Halawakee and Mountain Oak creeks) to native populations in the Tallapoosa River and to examine the effect of the introduction on the native Chattahoochee River fish community. Absent during the 1981–1985 survey of Mountain Oak Creek, the rough shiner was the fourth most abundant species (10.5% of catch) taken in 1995. In Halawakee Creek mean relative abundance of rough shiner increased from 9.8% in 1971 to 19.8% in 1995. The rough shiner was not collected above the milldam in Halawakee Creek during the historical and contemporary surveys. The rough shiner tended to be more abundant in Halawakee Creek than in its native Tallapoosa River (t = −2.11; df = 11; P = 0.06), where species richness is higher. In Mountain Oak Creek, blacktip shiner (Lythrurus atrapiculus) and golden shiner (Notemigonus crysoleucas) were abundant historically...