Relationships between body size, wing morphology, and perch height selection in a guild of Libellulidae species (Odonata)

Abstract

Ten common libellulid species perch along the shoreline of lakes and ponds in South Carolina, USA. We collected individuals at five ponds throughout summer 2005, weighed them in the field, and calculated wing loading (N·m²) and wing aspect ratios from digital photographs. We measured the perch-height preferences of these species in ‘low perch’ (10, 20, 30, and 40 cm) and ‘high perch’ (20, 40, 60 and 80 cm) experiments. Flywheel anemometers recorded wind speeds at each perch height. Species differed significantly in mean body mass, spanning nearly an order of magnitude from Perithemis tenera (67 mg) to Libellula vibrans (633 mg). There were also significant differences in wing morphology that correlated with mean mass; larger species had greater wing loadings and greater wing aspect ratios that smaller species. Species also differed significantly in their perch-height prereferences in both experiments, in a manner correlating with body mass and hindwing aspect ratios. Erythemis simplicicollis and P. tenera preferred short perches, Celithemis fasciata, Pachydiplax longipennis and Plathemis lydia used perches of intermediate height, and Libellula auripennis, L. cyanea, L. incesta, L. luctuosa, and L. vibrans preferred the tallest perches. Because mean wind speed and maximum wind speed also increased with perch height, larger species may prefer taller perches to experience greater wind speed and generate more compensatory lift to offset their larger wing loadings. However, it is also possible that correlations between body mass and perch height are the result of large species competitively restricting smaller species to lower perches.

Keywords: Odonata, dragonfly, odonate assemblage, Libellulidae, competition, perch, niche partitioning, body size, wing loading, aspect ratio

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