Environmental variability and the population dynamics of the exotic Daphnia lumholtzi and native zooplankton in Lake Texoma, U.S.A.

Abstract

Daphnia lumholtzi has invaded the U.S. from its original distribution of Africa, southern Asia and Australia. We examined the factors that affected the abundance and distribution of D. lumholtzi during 1994–1995 in Lake Texoma, a large southern plains reservoir. Daphnia lumholtzi was most abundant during summer months when temperatures were highest. The population exhibited a distributional shift in mid July from the upstream, more riverine portion of the reservoir to the cooler area near the dam when epilimnion temperatures upreservoir exceeded 30 °C. The pattern of variation in distribution and abundance did not correspond to the spatio-temporal patterns of most other resident zooplankton, nor did it correspond to changes in the phytoplankton assemblage. We conclude that the ability of D. lumholtzi to withstand the physiological effects of high temperature on reproduction and survival have a strong influence on the distribution and abundance of this organism in Lake Texoma. Furthermore, because D. lumholtzi became abundant only in the summer, after the decline of many of the native zooplankton, we suggest that it probably has little competitive impact on the other members of the zooplankton assemblage.