Synergistic effects of food shortage and an insecticide on a <Emphasis Type="Italic">Daphnia</Emphasis> population: rapid decline of food density at the peak of population density reduces tolerance to the chemical and induces a large population crash |
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Authors: | Hirokazu Takahashi Takayuki Hanazato |
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Institution: | (1) Division of Science for Inland Water Environment, Institute of Mountain Science, Shinshu University, 5-2-4 Kogandori, Suwa 392-0027, Japan |
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Abstract: | Laboratory populations of cloned Daphnia magna were exposed at different population phases (growing phase, density peak, stable phase) to the insecticide carbaryl at 15
μg 1−1, which was harmful to juveniles but not to adults, and their population dynamics were analyzed. The population declined most
at the density peak, when not only juveniles but also many adult individuals died. To analyze the factors affecting population
vulnerability to carbaryl, acute toxicity tests were conducted using Daphnia individuals of different body sizes under different food conditions. The test revealed that daphnid sensitivity to carbaryl
increased greatly when food density was changed from a high food level to a low level. This food condition, of low availability,
might be the condition to which the Daphnia populations were exposed at their density peak. The synergism of the negative impacts of anthropogenic and natural stresses
such as insecticides and food shortage may control aquatic populations. |
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Keywords: | Insecticide Daphnia Food concentration Toxicity Population dynamics |
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