Shade alone reduces adult dragonfly (Odonata: Libellulidae) abundance

We demonstrate that physical habitat conditions influence adult dragonfly (Odonata: Anisoptera) riparian site selection. In naturally treeless riparian areas of South Africa, invasive trees create shade and reduce native vegetation. We hypothesized that most breeding odonates select riparian areas (1) without shade, and (2) with high density and variety of understory perch structures. In two experiments at reservoir shorelines, we varied shade and perch structures. Dragonfly abundances (predominantly Trithemis species) were lower at sites with high (75%) or moderate (55%) shade cover than at sites with no shade, and lower at bare sand sites than sites containing stick perches. Perch density and variety (variety of heights and diameters) did not affect dragonfly abundance. These results indicate that shade alone directly reduces dragonfly habitat selection, isolating one aspect of habitat change that can alter insect behaviors.