An inverse elevational species richness gradient of Caucasian vascular plants and Encyrtidae (Hymenoptera, Chalcidoidea)

The elevational gradient in biodiversity, i.e. the decrease in species richness with increasing altitude, is well established in ecology. Here, we examined the respective gradient of parasitic hymenopterans (Encyrtidae) and plants in the Lagodekhi National Park (Country of Georgia) across an elevational gradient from 665m to 2559m a.s.l. by means of a year-round sampling of insects and a seasonal sampling of plants. Contrary to expectation, we found species richness of both taxa to peak at highest elevations. This unusual pattern was related to particular shifts in vegetation types, from relatively species-poor forests over rich grasslands towards poorer highland scrub vegetation. Our results call for a closer look at elevational gradients and highlights the need for including vegetation types in the assessment of altitudinal diversity gradients.