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Surveyed dragonfly abundances in and near fish-containing and fish-free ponds.We sorted dragonfly species into three size categories, small, medium and large (see Methods for dragonfly genera in each category). a, There were more larval individuals from the medium (grey bars) and large (black bars) size classes of dragonfly species, and fewer individuals from the small size classes (white bars), in ponds without fish than in ponds with fish (MANOVA: Pillai trace = 0.99, F3,4 = 19.96, P < 0.01; univariate F-tests for large species, F1,6 = 93.12, P < 0.001; for medium species, F1,6 = 85.67, P < 0.002; and for small species, F1,6 = 114.42, P < 0.001). b, The abundance of adult dragonflies was lower near ponds with fish (ANOVA: F1,6 = 10.85, P < 0.02). There was a difference between the abundances of adult medium and large dragonfly species near fish-free ponds and near ponds with fish (MANOVA: Pillai trace = 0.82, F3,4 = 5.89, P = 0.06; univariate F-tests for large species, F1,6 = 22.97, P < 0.003; and for medium species, F1,6 = 7.50, P < 0.03); there was no difference in small dragonfly density between fish-containing and fish-free ponds (F1,6 = 1.52, P > 0.26). Results are shown as means s.e.m.

Surveyed dragonfly abundances in and near fish-containing and fish-free ponds.We sorted dragonfly species into three size categories, small, medium and large (see Methods for dragonfly genera in each category). a, There were more larval individuals from the medium (grey bars) and large (black bars) size classes of dragonfly species, and fewer individuals from the small size classes (white bars), in ponds without fish than in ponds with fish (MANOVA: Pillai trace = 0.99, F3,4 = 19.96, P < 0.01; univariate F-tests for large species, F1,6 = 93.12, P < 0.001; for medium species, F1,6 = 85.67, P < 0.002; and for small species, F1,6 = 114.42, P < 0.001). b, The abundance of adult dragonflies was lower near ponds with fish (ANOVA: F1,6 = 10.85, P < 0.02). There was a difference between the abundances of adult medium and large dragonfly species near fish-free ponds and near ponds with fish (MANOVA: Pillai trace = 0.82, F3,4 = 5.89, P = 0.06; univariate F-tests for large species, F1,6 = 22.97, P < 0.003; and for medium species, F1,6 = 7.50, P < 0.03); there was no difference in small dragonfly density between fish-containing and fish-free ponds (F1,6 = 1.52, P > 0.26). Results are shown as means s.e.m.

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Predation can be intense, creating strong direct and indirect effects throughout food webs. In addition, ecologists increasingly recognize that fluxes of organisms across ecosystem boundaries can have major consequences for community dynamics. Species with complex life histories often shift habitats during their life cycles and provide potent condu...

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