Doctoral Dissertations

Date of Award

12-1999

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Ecology and Evolutionary Biology

Major Professor

Dewey L. Bunting II, Thomas G. Hallam

Committee Members

James Drake, David Etnier, Jacqueline Grebmeier

Abstract

The introduction of a species generates interest in its life history, ecosystem impacts,and reasons for successful colonization. Daphnia lumholtzi is an introduced zooplankton species native to Africa, Australia, and Asia. The first report of D. lumholtzi was in 1991 in Fairfield Lake, Texas. Since 1991, D. lumholtzi has become widespread throughout the southwest and south central states and as far north as Ohio. In Tennessee, D.lumholtzi has dispersed throughout many of the Tennessee Valley Authority reservoirs.To study the dynamics of D. lumholtzi in a local aquatic system. Ft. Loudoun Reservoir,a riverine reservoir in the Tennessee Valley Authority system, was chosen for study.There were three objectives in this study; (1) to determine D. lumholtzi distribution and population densities over a five year period; (2) to assess the effects of temperature on growth, development, and reproduction; and (3) to calculate production for each season.Ft. Loudoun reservoir was sampled twice weekly over a period of five years to determine D. lumholtzi distribution and seasonal abundance patterns. Daphnia lumholtzi populations were limited to areas below river mile 625, with greatest abundance in the area between river mile 616 and Ft. Loudoun Dam. Because of the pattern of distribution that was detected, seven sites below river mile 616 were chosen the main sites for this study. The seven sites were chosen to represent a variety of habitats: four main chaimel areas, two stream-fed coves, and one blind cove. Four abiotic factors: dissolved oxygen,pH, temperature, and specific conductance were measured with each sample. The abiotic factors were measured to assess their influence on D. lumholtzi population dynamics.Population variation was evident over the five year period, with high abundance in 1993(16.99 L-1'), 1994 (75.4 L-1>/sup>), and 1996 (58.79 L-1), and low abundance in 1995 (4.2 L-1) and 1997 (0.75 L-1). To test the effect of temperature on instar duration and longevity, D. lumholtzi were reared in the laboratory at seven experimental temperatures, ranging from 13°-28°C.Observations began from birth until the females died. The duration of individual instarsand the number of viable young for each adult female were recorded. The number of instars and the duration of each decreased with increases in temperature. At 28°C, the highest temperature used, instar duration was from one-half to one day as compared to 13°C which had durations of one and one-half to three days. Females reared at mid-range temperatures had durations that varied from three-quarter day to over two days. Both Males and ephippial females were found during the study. Male instar duration was kept separately. The behavior of ephippial females was observed and the effects of ephippia production was noted.Length-weight analysis was made during 1996, using samples from July 3, July 8,July 11, and July 18. Daphnia lumholtzi were divided into eight size groups ranging from 0.5 mm to < 1.6 mm, dried, and weighed. Based on statistical analysis, it was determined that the weight of each size group was related to the length; therefore, a common regression line could be used to estimate weights for other years. Production Was estimated for each sampling season using the growth increment summation method.The weight of each size group was summed for a site production estimate, sites were summed for a date estimate, and all dates were totaled for an annual production estimate.Production estimates varied from 18.42g C m-2 y–1 in 1996 to 0.08g C m -2 y -1 in 1997.

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