Evidence-based assessment of butterfly habitat restoration to enhance management practices

The decline in distribution and abundance of biodiversity requires evidence-based guidelines for cost-effective conservation management and systematic quantitative assessments of its effects. We investigated the efficiency of a habitat restoration programme aimed at reducing the risk of extinction of the Iolas blue Iolana iolas (Ochsenheimer, 1816), one of the rarest butterflies of Central Europe. Using occupancy and capture-mark-recapture (CMR) models accounting for probability of detection, we assessed habitat patch occupancy, habitat selection, demography and dispersal with the aim of testing and refining restoration measures. Count surveys performed at 38 plantations dedicated to the species’ unique host plant resulted in an occupancy rate of 50 %, with mostly very low relative abundance indices. The site-occupancy habitat analysis demonstrated that species abundance was best explained by host plant vitality, habitat patch connectivity, and solar radiation. CMR surveys yielded very high catchability (82 %), individual detectability (86 %) rates and limited dispersal capacity. These results form the basis for future efficient count surveys to assess species distribution and abundance. They also provide evidence-based recommendations for improving ongoing habitat restoration: (i) the attractiveness of host plant plantations must be enhanced by promoting mass blossoming, which can be achieved through systematic autumn pruning of the extant plantations; (ii) new plantations should be created in order to fill in the gaps in the landscape matrix, to increase meta-population capacity through improved habitat connectivity. Finally, this study demonstrates the relevance of efficiency tests as an integral, adaptive phase of any conservation research activity.