Abstract

Similar morphology and confused historical taxonomy of Hybognathus hankinsoni (brassy minnow) and Hybognathus placitus (plains minnow) have made determination of their historic distributions and conservation status unclear in eastern Colorado basins. We developed logistic regression models from morphometric measurements to predict species identity of Hybognathus collections from Colorado and adjacent counties (n = 1154 specimens in 134 lots). A model based on orbit diameter, standard length, and eye position correctly predicted 98% of the specimens examined and 100% of the museum lots. Hybognathus hankinsoni have larger eyes centered on a horizontal line through the tip of the snout, whereas H. placitus have smaller eyes centered above the tip of the snout. The two species were historically sympatric in the Platte, Republican, and Smoky Hill River basins, whereas H. placitus was allopatric in the Arkansas River basin. The taxonomic characters defined here will allow accurate identification of future collections to determine the status of these native fishes.

Abstract

Studies of diet overlap of insectivores, especially lizards, have been important for the development of much ecological theory. However, measures of overlap, usually based on dietary volumes, vary widely among studies. Most researchers estimated the volumes of prey in stomach contents subjectively or attempted to reconstruct the volume of individual prey items from linear measurements of length (L), width (W) and/or height (H), or from mass. We studied the relationship between indices of volume based on indirect measures and direct measures of volume by fluid displacement for a collection of arthropods that simulated the diet of a generalist lizard. For each individual arthropod, we calculated the proportional error [(measured volume—estimated volume)/measured volume)] for each estimation method. For individual large insects, there were significant differences between orders in the proportional error for all methods. The methods based on linear measurements had only weak relationships (r ² ≤ 0.4 in all cases) with measured volume. Mass had a stronger (R ² = 0.9), but curvilinear relationship with measured volume. For the combined masses of all arthropods in each diet category from stomach contents of four species of lizards, there were also significant differences in the proportional error between arthropod orders for all methods (P ≤ 0.018 in all cases), except for mass (P = 0.126). Because most indices of overlap are based on proportions, errors in estimation for any one category affect the degree of overlap for all other categories found in that stomach. Cluster analysis of different indices based on the same data indicated differences of up to 10% in proportional overlap. Such large differences for identical diets mean that it is extremely difficult to compare studies that used different methods of volume estimation. We conclude that the use of general formulas to reconstruct the volumes of arthropods are not appropriate for most studies of diet overlap and that extreme care should be exercised in attempts to perform meta-analyses on studies that purportedly measured prey volumes.

Abstract

Catfishes of the genus Ameiurus are a well-known component of the North American ichthyofauna. J. G. Lundberg estimated phylogenetic relationships among species of Ameiurus according to morphological variation. Two clades containing the extant species were recovered: the natalis clade (Ameiurus natalis, Ameiurus melas, and Ameiurus nebulosus) and the catus clade (Ameiurus serracanthus, Ameiurus catus, Ameiurus platycephalus, and Ameiurus brunneus). Original nucleotide sequence data were collected from mitochondrial (cytochrome b) and nuclear (recombination activation gene 2) genes and used to test the predictions of the hypothesis based on morphological data. The monophyly of both natalis and catus clades was rejected by the nucleotide dataset and an alternative phylogenetic hypothesis is provided.

FAO SPECIES IDENTIFICATION GUIDE FOR FISHERY PURPOSES. THE LIVING MARINE RESOURCES OF THE WESTERN CENTRAL PACIFIC. Carpenter, K. E. and V. H. Niem (eds.). Volume 1, Seaweeds, corals, bivalves, and gastropods, 1998, p. 1-686, ISBN 92-5-104051-6. Volume 2, Cephalopods, crustaceans, holothurians, and sharks, 1998, p. 687–1396, ISBN 92-5-104052-4. Volume 3, Batoid fishes, chimaeras, and bony fishes part 1 (Elopidae to Linophrynidae), 1999, p. 1397–2068, ISBN 92-5-104302-7. Volume 4, Bony fishes part 2 (Mugilidae to Carangidae), 1999, p. 2069–2790, ISBN 92-5-104301-9. Volume 5, Bony fishes part 3 (Menidae to Pomacentridae), 2001, p. 2791–3380, ISBN 92-5-104587-9. Volume 6, Bony fishes part 4

INCORPORATING UNCERTAINTY INTO FISHERY MODELS. J. M. Berkson, L. L. Kline, and D. J. Orth (eds.). 2002. American Fisheries Society Symposium 27, Proceedings of the Workshop Incorporating Uncertainty into Fishery Models held at Jekyll Island, Georgia, USA, 28–29 June 1999. American Fisheries Society, Bethesda, Maryland. ISBN 1-888569-31-X. xii + 196 p. $69.00 (paperback).—WDA Jr.

WHIRLING DISEASE: REVIEWS AND CURRENT TOPICS. J. L. Bartholomew and J. C. Wilson (eds.). 2002. American Fisheries Society Symposium 29, Proceedings of the Seventh Annual Whirling Disease Symposium held at Salt Lake City, Utah, USA, 8–9 February 2001. American Fisheries Society, Bethesda, Maryland. ISBN 1-888569-37-9. x

A New Species of the Banjo Catfish Genus Ernstichthys (Siluriformes: Aspredinidae) from the Bermejo River Drainage, La Plata Basin, Argentina

Gastón Aguilera,

Guillermo E. Terán,

Alejandro Méndez-López,

Martín Miguel Montes, and

Tiago P. Carvalho

Ostracion knorrii Walbaum, 1792, a Senior Synonym of the Striated Frogfish Antennarius striatus (Shaw and Nodder, 1794) Invalidated by “Reversal of Precedence”