Population ecology of Ephydra cinerea Jones (Diptera: Ephydridae), the only benthic metazoan of the Great Salt Lake, U.S.A.
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The population of Ephydra cinerea was studied during three summers when dissolved solids levels were about 130 g/l. All life stages are present year-round, but there is apparently some coordination of the initial pulse of adult emergence in June. There are probably 1–2 generations per year.
Eggs are deposited on the water surface; inputs to three locations were similar. Larvae successfully avoid the large benthic area covered by an anaerobic monimolimnion. They tend to immigrate from substrates where they grow relatively poorly, and to remain on substrates where they grow better. Consequently, larval densities are more than ten times higher on reef and shallow water mud substrates than on sand. This marked spatial specialization in the absence of substrate-specific predators or competitors illustrates the power of habitat quality by itself in determining spatial patterns of abundance in a lake.
Experiments showed larval growth on the reef was inversely related to density, and the lake as a whole produced relatively larger flies in a year when larval and pupal densities were relatively low. Yearly production by E. cinerea is roughly 50 g/m2, about 88% of which comes from reefs and shallow water mud areas covering only 18% of the bottom area.
Past studies indicate that blue-green algae dominate the lake's benthic flora when salt concentrations are high (due to low lake levels), and diatoms take over when salt concentrations are low. Fly abundance appears to be inversely related to salinity.
The lake's present high planktonic primary production is equal to that of eutrophic freshwater lakes, yet it has water clarity more characteristic of an oligotrophic lake. The high water clarity (which makes possible the high benthic production) probably depends on the absence of phytoplankters that can both tolerate the high salinity and avoid being eaten by Artemia salina. Continued dilution of the lake will probably upset this situation and result in reorganization of the lake's energy flow pattern.
Keywordscompetition density manipulations habitat selection population regulation secondary production spatial distribution substrate preferences
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