Abundance and diversity of dragonflies four years after the construction of a reservoir

Abstract

Few studies have investigated the impacts of river impoundments on reservoir constructions. Reservoir construction deeply changes dragonflies' habitat structures, especially in relation to shoreline vegetation. This study investigated the effects ofthe impoundment of the Guadiana River and its tributaries on dragonflies four years after the construction of a reservoir. A total of 17 dragonfly species (11 Zygoptera and ten Anisoptera), representing six families, were recorded in 21 sites in the years 1999 and 2003. Aeshna mixta, Coenagrion caerulescens, Coenagrion scitulum, Sympetrum foscolombei, Sympetrum meridionale and Sympetrum striolatum were sampled just before the impoundment took place, and Anax parthenope, Onychogomphus forcipatus, Orthetrum coerulescens, Trithemis annulata, Platycnemis acutipennis and Platycnemis latipes were recorded only after the construction of the reservoir. We concluded that the construction of the Alqueva Reservoir four years earlier did not change the dragonfly species richness, possibly because of species overlap, but that the species composition was modified. Changes in marginal vegetation may have been important to new species compositions.