Foraging modes in an assemblage of odonate larvae ? effects of prey and interference

Abstract

The foraging behaviour of four coexisting odonate larvae; Coenagrion hastulatum (Charp.) Zygoptera, Aeshna juncea (L.) Anisoptera, Cordulia aenea (L.) Anisoptera and Leucorrhinia dubia (v d Lind.) Anisoptera was analysed under various conditions of prey type and abundance. Coenagrion and Aeshna used a sit and wait mode when the prey density was high and when the prey was evasive. When the prey abundance was low an active mode was used. In Aeshna an active mode was also used when prey was sedentary. Cordulia exhibited a sit and wait mode and Leucorrhinia an active mode under all prey treatments performed. The results indicate that a niche differentiation in foraging behaviour may be one of several ways to reduce food competition between these coexisting species. However a literature study on prey selectivity did not reveal any support for this suggestion. Interference from Aeshna altered the foraging behaviour of Coenagrion whereas that of Leucorrhinia remained unchanged. Further, Aeshna preyed heavily on Leucorrhinia and to a lesser extent on Coenagrion during interference trials. A field study did not show any negative correlation in abundance between Aeshna and Leucorrhinia or Coenagrion larvae. The results indicate interference competition may be more important than exploitation competition in the shaping of odonate larval communities.