Competitive interactions affect perch-height preferences of three Odonata taxa (Coenagrionidae, Libellulidae)

Abstract

Co-occurring odonate species often perch at different heights. We studied the effects of interspecific and intraspecific interactions on perch-height selection by Perithemis tenera, Pachydiplax longipennis, and Enallagma spp. by creating artificial perch stations and comparing perch selection when species perched alone or together. We also compared the frequency of perch-height use in the presence or absence of P. tenera and P. longipennis decoys (dead mounted specimens). When species perched alone, Enallagma spp. preferred low perches, P. tenera intermediate perches, and P. longipennis tall perches. This correlated with body mass; larger species used taller perches. Intraspecific responses to decoys were species specific; P. tenera showed an aggressive positive response to the presence of a conspecific decoy, whereas P. longipennis avoided conspecific decoys by shifting to lower perches. Interspecific effects were more consistent. The presence of living or decoy P. tenera at a station caused Enallagma to shift to lower perches. Likewise, the presence of living or decoy P. longipennis at a station caused P. tenera to shift to lower perches. Reciprocal effects were insignificant. These interactions were defined as interference competition because, in the decoy trials, perch-height shifts occurred although all four perches were available to visitors. We conclude that asymmetrical competition contributes to perch-height selection among these species.

Key words:

• Odonata
• dragonfly
• Enallagma
• Perithemis tenera
• Pachydiplax longipennis
• competition
• perch
• niche partitioning