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An experimental test of Dodson’s hypothesis that Ambystoma and Chaoborust have complementary feeding niches Giguère, Louis

Abstract

The removal from an alpine pond of the eggs of a salamander, Ambystoma gracile, had a large impact on the zooplankton community. The pond was dominated by large Daphnia while nearby ponds, from which salamander eggs were not removed, were dominated by the small cladoceran Diaphancscma . The size at maturity of Diaptomus copepods increased by 0.3 to 0.4 mm compared to the previous year. Crop content analyses revealed that food intake of Ilnd and Illrd instar Chaoborus was low. IVth instars were scarce and their dry weight was 50% lower than in the previous year. When Ambystoma is abundant, it preys heavily upon Holopedium gibberum and Daphnia rosea which are not available as food to Chaoborus trivittatus. The reduction in the density of large zooplankters permits a competitor, Diaphancscma brachyurum , to flourish. It is the main food source, when available, of Ilnd and Illrd instar Chaoborus . In this indirect way, Chaoborus depends on vertebrate predation to successfully reach its IVth instar. This lends support to Dodson's hypothesis of complementary feeding niches.

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