Competition, predation and microhabitat selection of Zygoptera larvae in a lowland river

The microdistribution of 4 lotic spp. was investigated in the field. Microhabitat selection of Calopteryx splendens and Erythromma najas was further examined in the laboratory, individually at different larval densities and in the presence of the other species and a predator. — E. najas, Ischnura elegans and Platycnemis pennipes showed significant preferences for particular aquatic macrophytes compared to others in the field, whereas C. splendens did not discriminate between the investigated plant species. Only limited spatial separation was apparent between the larvae of different species, as preferences for the same macrophyte species were found. — When kept separate and at low densities, larvae of C. splendens and E. najas inhabited significantly different microhabitats in the laboratory. At high intraspecific abundances, spatial overlap between the two species became apparent as both increasingly occupied less preferred substrata, which is in concurrence with the ideal free distribution model of habitat selection. E. najas splendens at high densities. – In this instance, intraspecific competition therefore appeared to be more important than interspecific competition with other Zygoptera in determining the microdistribution of E. najas. In the field, the niches of the two species may be more adequately separated on the basis of prey selection or hunting behaviour. E. najas also actively reacted to the presence of a predator, indicating some flexibility of response regarding perch selection.