Providing evidence for the conservation of a rare forest butterfly: Results from a three-year capture-mark-recapture study

Abstract

Species living in spatially structured populations require a network of interconnected habitat patches. Due to changes in forest management, this network of habitat patches has been lost for insect species inhabiting open spots within forests. We studied two of the last populations of the Southern White Admiral (Limenitis reducta) in Germany. The aim of our study was to provide information for the conservation of this species. We conducted a capture-mark-recapture study over three consecutive years and we estimated population sizes and demographic parameters using Jolly-Seber and Cormack-Jolly-Seber models. Furthermore, we used different dispersal kernels to study the dispersal of L. reducta. We found that apparent survival rates differed greatly between the sexes. The mean residence times were eight to nine days for males and only two to four days for females. Apparent survival rates of both sexes decreased with increasing wing deterioration. Total population sizes of L. reducta varied between sites and years and ranged between 61 and 123. Daily abundances were generally low, especially that of females. The mean dispersal distance of individual recaptured butterflies increased in years with higher population densities, suggesting density-dependent dispersal. The dispersal data in our study was clearly bimodal, probably reflecting ‘routine movement’ at short distances and ‘displacement movement’ between habitat patches at longer distances. Consequently, the processes generating the dispersal data were better represented by the lognormal mixture model than by the negative exponential and the inverse power function. The mixed kernel predicted that about 9 % of the population disperses over > 1 km but that long-distance dispersal is rare. Our study highlights the urgent need for conservation measures to protect L. reducta in Germany and, based on our data, we recommend to create new habitat patches at distances of 1 to 1.5 km from existing habitats.