Microclimate and biotic interactions affect Karner blue butterfly occupancy and persistence in managed oak savanna habitats

Abstract

Factors affecting site microclimate are important for the maintenance of populations, particularly during stochastic weather events. The federally endangered Karner blue butterfly (Lycaeides melissa samuelis Nabokov) has faced population declines throughout its range, most recently in 2012 following a severe drought throughout the Great Lakes region. This research builds upon previous work to understand what microclimate and biotic factors predict L. m. samuelis site occupancy. To gain an understanding of what habitat characteristics are conducive to L. m. samuelis survival during severe stochastic weather events, previously occupied sites were compared with currently occupied and restored sites in Allegan State Game Area, Michigan and the Oak Openings region of Ohio using variables significant in a predictive model. The heat load variable accounted for 64–67% of the variation in the model alone while individual biotic variables accounted for <5% of the model variation individually. The density of flowering lupine, ant entrance densities and heat load were higher in occupied sites while formerly occupied sites had higher woody stem density and canopy cover. These data show that site microclimate and factors affecting L. m. samuelis larval growth and reproduction affect distribution and persistence in stochastic environments. These findings can be incorporated in habitat management plans to create climate resilient refugia for current populations and increase the probability of reintroduction success in restored areas.