|Abstract or Summary
- 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
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.