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Large-scale operations management test of use of the white amur for control of problem aquatic plants : the herpetofauna of Lake Conway : species accounts

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Gross, Dena T.
Sutphen, Dareth A.
McDiarmid, Roy W.
Bancroft, G. Thomas
Godley, J. Steve
Rojas, N. Nan

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U.S. Army Engineer Waterways Experiment Station


Species accounts provided in this report summarize our knowledge of the natural history of the 30 species of amphibians and reptiles known from Lake Conway, Florida. The accounts focus on two major objectives of the Lake Conway herpetofaunal project: (1.) to identify spatial and temporal changes in life-history parameters of the component species, and (2.) to determine whether any observed changes were the result of the white amur aquatic plant control program. Important confounding factors influencing the ecological organization of the Lake Conway herpetofauna also were examined. Quantitative annual changes in at least one of nine measured ecological parameters were detected in 17 (56.7%) of the species during the three-year study (1977-1980). Among the 30 species, ecological changes were recorded for two of four salamanders, all eight frogs, the American alligator, five of ten turtles, and one of seven snakes. Of those species in which yearly variation was observed, most showed a change in relative density (N=15), followed by seasonal activity (6.), population structure (5), open water habitat use (4), food habits (4), and movement patterns (1). No yearly variation was detected in the use of specific littoral zone habitats, growth rates, or reproductive output per individual. Our ability to detect ecological changes was strongly dependent upon sample size for the species. Ecological shifts in the herpetofauna of Lake Conway were caused by at least nine factors, grouped into four general categories: white amur, human disturbance, natural phenomena, unknown. These causative agents often were operating simultaneously, and confounded the effects of the fish. Human disturbance, through shoreline development (N=14 species), destruction or removal of individuals from the lake system (N=2), boat propeller mortality (N=3), and investigator effects (N=4), was responsible for more changes in more species than any other category: two hylid frog species were extirpated from Lake Conway as a resuit of shoreline development. Annual fluctuations in water level (N=5 species) and weather conditions (N=6) affected some species. Four species experienced an ecological shift in which the causative agent(s) was not identified. One higher order interaction was detected in one species. The white amur was implicated as contributing to or directly causing distinct annual shifts in the ecology of one salamander and three turtle species. These species exhibited changes in the use of open water habitats (N=4 species), population structure (N=1), density (N=3) , and food habits (N=3) , which were attributable to the effects of the fish. Thus, macrophyte removal by white amur, acting in concert or perhaps synergistically with other disturbance phenomena, has caused significant ecological changes in the herpetofauna of Lake Conway.


Miscellaneous Paper


Amphibia, Amphibians, Reptiles, Aquatic animals, White amur, Ctenopharyngodon idella, Grass carp, Biocontrol, Biological control, Aquatic plant control, Lake Conway (Fla.), Ecosystems, Ecology, Aquatic ecology, Aquatic Plant Control Research Program (U.S.)


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