Graduate Thesis Or Dissertation
 

Biology and downstream drift of some Oregon Ephemeroptera

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  • Six species of Ephemeroptera were studied in two sample areas in Western Oregon: the Metolius River, Jefferson Co., and Oak Creek, Benton Co. The Metolius River is characterized by low fluctuations in flow and water temperatures (8-13 C); whereas, Oak Creek is characterized by large fluctuations in volume of flow (6X or more) due to winter rains and by high summer water temperatures (22 C). Keys or descriptions are presented for identifying the nymphs of all species and the adult females of Paraleptophlebia. Each sample area was divided into four biotopes, and each was sampled, alternate months in the Metolius River and monthly in Oak Creek, by using a stovepipe (6 in. dia.) and a fine meshed aquarium net. Drift samples were taken monthly in Oak Creek. Specimens were counted, measured for length, and divided into age groups ranging from newly hatched (Group I) to ultimate instar nymphs (Group V). All six species were found in both streams. Baetis bicaudatus Dodds had two generations per year in the Metolius River, but one per year in Oak Creek, In Oak Creek nymphs of the second generation may be killed by high summer temperatures, and the species survives the warm period in the egg stage. Baetis tricaudatus Dodds (Oak Creek only) had multiple but an undetermined number of generations per year. The cycles of Baetis parvus Dodds, Paraleptophlebia temporalis (McDunnough), and Cinygmula reticulata McDunnough were similar in both areas (one generation per year; hatching in fall, emergence in spring), but the period of adult emergence is shorter and earlier in Oak Creek. Paraleptophlebia debilis (Walker) (Oak Creek only) hatched in early spring and completed emergence by November (one generation per year). Beginning with the species that lived in slowest current and in silty substrate and proceeding to that which lived in fastest current, the sequence was: P. debilis, P. temporalis, B. parvus, C. reticulata, B. tricaudatus, and B. bicaudatus. All species were displaced to non-typical habitats during winter flooding (Nov. to Feb.). During flooding, density per unit area decreased 60%, but this was apparently due to increase in stream width, since the number per unit length of stream decreased only 20%. Drift rate was not directly correlated to habitat, since in Oct. and Nov., of three species found predominantly in the riffle, two were abundant in the benthos but scarce in drift, while the third species was scarce in the benthos but dominant in the drift. In the laboratory, drift rate could not be correlated with ability of a species to hold to the substrate, since the species with the least current resistance drifted little, while a species with great current resistance was dominant in the drift. The main effect of drift in Oak Creek was a temporary displacement of species from the chosen habitat. A conceptual model emphasizing additive components of drift is discussed.
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