Comparative ecology of four species of darters (Etheostominae) in Lake Dauphin and its tributary, the Valley River
The johnny darter Etheostoma nigrum, Iowa darter Etheostoma exile, river darter Percina shumardi, and logperch Percina caprodes occur in Lake Dauphin and its largest tributary, the Valley River. Density and relative abundance of the four species in defined river and onshore lake environments were determined by seining throughout most of the ice-free period. In spring river darter and logperch moved into the lower reaches of the river and spawned; but after the reproductive season johnny darter were virtually the only darters remaining in the river. That species was more abundant in non-current than in current. In the lake unbroken sand or mud bottom (non-cover) was avoided by all darters. Beds of aquatic vegetation were inhabited by Iowa darter, with high densities of young-of-the-year occurring in late summer. Rubble beaches exposed to wave action were inhabited chiefly by river darter. Pebble-rubble beaches protected from wave action contained the greatest overlap of the four species, with johnny darter and Iowa darter prominent following the reproductive season. Preference experiments in the laboratory confirmed the avoidance of non-cover areas in the field, but failed to demonstrate preferences for particular types of cover. The smallest Iowa darter, river darter and logperch caught in the lake shared a diet consisting mainly of copepods and cladocerans, while small johnny darter in the river ate chiefly midge larvae. Larger fish took a variety of benthic foods. Two or more species of darters occurring together in the same environment at the same time usually ate the same range of foods but concentrated on different items. Differences in environment inhabited and food eaten indicate that the ways of life of the four species are sufficiently dissimilar to account for their coexistence in the same watershed.