Some aspects of mayfly (Ephemeroptera: Stenonema) ecology in a Neosho River riffle, Lyon County, Kansas.

Abstract

A study was conducted to determine the Stenonema species inhabiting a riffle of the Neosho River near Emporia, Kansas, and to observe strategies employed by the species present to reduce competition. For benthic sampling purposes, three substrate zones were recognized within the study reach, according, to median particle diameter. Md0 (median diameter in phi units) of the zones were: Zone I. -3.38, Zone II, -4.75, and Zone III, -6.25. Zone II comprised approximately 50r. of the study reach, with Zones I and III comprising approximately 25% each. From 11 June 1980 to 10 October 1980 water temperature ranged from 17.5°C to 32.0°C, dissolved oxygen ranged from 6.0 ppm to 8.9 ppm, and pH ranged from 7.89 to 8.33. Quantitative benthos samples were taken from 20 March 1980 to 24 September 1980. In addition, Stenonema nymphal and adult stages were collected qualitatively during the same period. Four species were collected: S. terminatum, S. femoratum, S. exiguum, and S. integrum. The objective to characterize resource partitioning strategies was not realized due to unexpectedly low population densities of all species present except S. terminatum. Populations of S. femoratum, terminatum nymphs within the study reach of 68.9 nymphs/m 2 July S. exiguum, and S. integrum were too sparse for reliable substrate preference and life cycle analyses. The maximum estimated density of S. 2 on 1980. There was no significant preference for any substrate zone by S. terrninatum n~nphs. Analyses of adult light trap data and measurements of nymphal head capsule width indicated that S. terminatum produced two generations during the summer of 1980 and a third~ fall generation which would mature in the spring of 1981. Known habitat requirements of S. femoratum. S. exiguum, and S. integrum were compared with conditions at the Emporia study reach. In each case, at least one requirement was lacking.