Two populations of Lirceus fontinalis Rafinesque in DeKalb County, Georgia are isolated in separate river drainages and evolving in response to different environmental stresses. Drought and high temperatures seem the main ecological factors limiting the population on Mount Arabia. These factors are of little moment to the population in Lullwater Creek where biotic factors are of primary ecological significance. Behavioral patterns associated with moisture, flowing water, and temperature fluctuations contribute to the ability of Mount Arabia Lirceus to survive climatic stresses and repopulate solution pits. Behavioral patterns associated with flowing water and light add to the ability of Lullwater Creek Lirceus to maintain their position in the continuously flowing stream and to avoid predators. Although they belong to the same specie morphologically, members of these two populations are not the same species physiologically and ecologically. They differ significantly in their respiratory rates, tolerance to anaerobic conditions, and to a combination of gamma radiation, high temperature, and drought stresses. Members of the two populations are considered to be ecotypes or races of L. fontinalis.
Population growth and concentration factors for 65Zn and 137Cs have been measured for Achnanthes brevipes Agardh, Carteria sp. Diesing, Chlamydomonas sp. Ehrenberg, Dunaliella salina Teod., Nannochloris atotnus Butcher, and Phaeodactylum tricornutum Lewin subjected to factorial combinations of eight temperatures (6–40 °C) and ten salinities (3.5–44.0 p.p.t.). Regression coefficients were calculated for polynomial models describing response surfaces for growth and radionuclide concentration. Salinity was more important than temperature in describing population growth for Carteria, Dunaliella, Nannochloris and Phaeodactylum. No independent variable was consistently of primary importance in describing 137Cs concentration factors, while temperature accounted for more variation in 65Zn concentration factors than salinity or population growth in all algae except Dunaliella. Concentration factors for 65Zn were uniformly higher than 137Cs concentration factors.
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