, Volume 4, Issue 4, pp 431-439

Hydrologic Connections and Overland Dispersal in An Exotic Freshwater Crustacean

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Abstract

Organisms living in lakes face the problem of dispersing through an uninhabitable matrix in order to reach suitable habitat. One possible mechanism for moving between lakes is by surface water connections. We used a seven-year data set to investigate the spread of the exotic cladoceran Daphnia lumholtzi among Missouri reservoirs with respect to stream connections. Reservoirs that were downstream of known populations of D. lumholtzi were more likely to become invaded than those that were not. However, invasion likelihood was only weakly related to the presence of upstream source populations, and reservoirs without potential upstream sources were colonized at a rate of 7.3% per year. The difference in invasion rate between lakes with and without upstream sources varied among years, and was significant in only two of the six years of study. In addition, the higher invasion rate of downstream lakes could be explained by their greater surface area. These patterns suggest that surface water connections may form one means of dispersal for D. lumholtzi, although overland movement is also important. The ability to utilize several modes of dispersal may explain the rapid expansion of this species' range since its arrival in North America.