Notropis

Abstract: The relationship between spatial preference and diet in four species of the genus Notropis (Pisces: Cyprinidae) was investigated in Roxbury Creek, a small stream in southern Wisconsin. Characteristic spatial distributions for each species were determined from frequency of catch in unbaited minnow traps set at varying heights and locations in the pools of the stream. Data for the year 1966—67 indicate that two species, Notropis atherinoides and N. spilopterus are common in midwater. Notropis dorsalis is most frequently found near the bottom and shows a strong preference for the upstream edge of pools Notropis stramineus is also found most often near the bottom but within the pools themselves. The spatial distributions of aquatic invertebrates, the major prey of Notropis in the pools of Roxbury Creek, were also investigated. Data gathered from drift and bottom samples taken in eight sampling periods during 1970—71 suggest a separation between the relatively sedentary bottom fauna, composed of oligochaetes, isopods, several genera of chironomids, tipulids, and trichopterans; and the drift fauna, composed of copepods, chironomids of the subfamily Orthocladiinae, ephemeropterans, and terrestrial anthropods. Certain genera, including the ubiquitous Gammarus were found commonly in both drift and benthic samples. Indices of similarity between pool benthos and drift ranged between 7% and 59%. Data on food habits of Notropis gathered from stomach content analysis of fishes collected over the same period indicate that 73% of the invertebrate genera present are utilized by Notropis species in Roxbury Creek. Considerable overlap exists in the invertebrate genera chosen by the four species (69%—84%), and strong overall correlations between species are found in the importance of various orders of aquatic invertebrates in the diet. Differences in food habits relate principally to differences in space utilization. Midwater species tend to feed on drifting chironomids, copepods, terrestrials, and other animals found in the water column. Bottom—dwelling fishes feed on benthic genera of chironomids, tipulids, oligochaetes, and other organisms found commonly in pool substrates. It is concluded that spatial rather than taxonomic considerations are the chief determinants of prey selection in these four species, and that this pattern of resource subdivision acts to reduce competition in sympatric, syntopic populations of these fishes. Data from other Wisconsin Streams, from aquarium observations, and from literature review suggest that multispecific assemblages of mutually responsive species like the ones in Roxbury Creek are common in Notropis.

Abstract: Hybrid zones in fluvial fishes may be heterogeneous from drainage to drainage. The comparison of data from morphology, allozymes, and mitochondrial DNA (mtDNA) indicates variability in the causes and degree of restriction of gene flow between Notropis cornutus and Notropis chrysocephalus. Allozyme marker loci show frequency-dependent introgression; i.e., the rarer species, whichever it is at a particular locality, tends to exhibit a higher proportion of introgressed alleles. Unlike allozymes, introgression of mtDNA haplotypes varies geographically. In westward-flowing Michigan drainages, N. cornutus mtDNA haplotypes are more common in F1 hybrids and backcrosses, independent of parental frequencies. In eastward-flowing Michigan drainages, N. chrysocephalus mtDNA is more common in F1 hybrids and backcrosses; this pattern may be due to local ecological effects or frequency-dependent introgression. Morphological data alone are not sufficient to distinguish all classes of hybrids. The lack of concordance of morphological, allozymic, and mtDNA introgression patterns implies operation of one or two factors: 1) geographically variable patterns of selection against different hybrid and backcross combinations or 2) genetic differences between Michigan populations inhabiting eastward- and westward-flowing drainage systems accumulated during historical isolation.

Abstract: Twenty-nine species of fishes were collected in the middle and upper Colorado River basins in 1967-1973. The native suckers, Catostomus latipinnis and C. discobolus, were the dominant species in the study area. Introduced species outnumbered native species 19 to 10. The introduced Ictalurus punctatus and Notropis lutrensis were abundant throughout most of the upper basin. The abundance of introduced species has increased steadily since 1900 as has the introductions of new species. Four endemic species, Ptychocheilus lucius, Gila elegans, Gila cypha, and Xyrauchen texanus, are considered endangered. These rare forms reproduce in the lower Yampa River, Desolation Canyon of middle Green River, and the lower Green River in Canyon-lands National Park. The major reasons for the decline of native fishes are considered to be alterations of habitat by high dams and introductions of exotic species.

Abstract: Flooding on the Devil's River, Texas, caused changes in both physical and biological structure of the river. Habitat types became less distinct and generally more riffle-like. Fish species diversity, evenness and number of species decreased. Higher diversities were expressed nearer the river's terminus, indicating flood-resistance there. Prior to the flood 18 species associations existed; 13 existed after flooding, only three of which were present prior to flooding. Six species dominated both preand post-flood community biomass and maintained the same rank-order dominance in both flood regimes. These (Dionda episcopa, Notropis proserpinus, N. amabilis, Astyanax mexicanus, Notropis venustus and Dionda diaboli) occupied slightly different habitats or utilized different resources of the same habitat in the post-flood regime. All are adapted to a flood-prone environment and may constitute the greatest degree of faunal stability in the ecosystem.