Abstract:
The coexistence of Daphnia sp. inhabiting Lake Reading, a 55 ha lake 19 km northeast of Emporia, Kansas, was studied during the period 1980 to 1982. Plankton samples were collected throughout the period March to July of each season. Samples consisted of vertical tows from a depth of two meters to the surface, taken from 12 different locations on the lake, using a 30 cm diameter, 64 micron mesh plankton net. Standing crops, species composition, seasonal occurrences, body lengths, and egg production of Daphnia galeata mendotae, Daphnia ambigua, and Daphnia parvula during the 1980 to 1982 seasons were recorded. Selected physicochemical conditions, water temperature, dissolved oxygen, pH, and specific conductances were also recorded during each sampling
period. The season of occurrence for Daphnia in Lake Reading was from approximately 15 March to 15 July during each year of the study. Before 1979, ~. parvula was the most abundant and often the only daphnid species found in the lake. Daphnia galeata mendotae was the most abundant species during 1980 and 1981, but shared the role of dominant species with D. ambigua in 1982. Daphnia ambigua showed peak population densities in May, while D. galeata mendotae and D. parvula populations reached their maximum densities in June and July. Egg production was greatest for each species 8-16 days prior to the time peak population densities occurred. Daphnia parvula individuals produced more eggs than individuals from D. galeata mendotae and D. ambigua, as reflected by mean brood size per gravid female and the number of eggs produced individual-l day -1
Daphnia galeata mendotae was the largest species of daphnid in the lake during 1982, followed in order by D. parvula and D. ambigua. There were significant differences, at p=O.OS, between mean body lengths for D. galeata mendotae and D. ambigua, and between D. parvula and D. ambigua, but not between D. galeata mendotae and D. parvula.
