Interacting grassland species under threat of multiple global change drivers

Aims: Multiple environmental changes simultaneously altering the biotic and abiotic context of species are threatening communities and ecosystems worldwide. Exploration and mitigation of the eco-evolutionary impacts of global change threats correspondingly are major components of conservation research, yet joint global change impacts remain poorly studied. Moreover, changes in the biotic context of species are rarely considered when assessing global change-induced range shifts. We aim to unravel the contributions of habitat fragmentation, climate warming, genetic variation and biotic interactions to the past, current and future distribution of a rare grassland butterfly. Location: French Pyrenees. Taxon: Phengaris (Maculinea) alcon, Gentiana pneumonanthe. Methods: We examined the combined effects of habitat fragmentation and climate warming on the expected distribution of a specialized grassland butterfly and its host plant species using ecological niche modelling and genetic analysis. More specifically, circuit theory and maximum entropy modelling were used to assess changes in connectivity and habitat suitability under various land use and climate warming scenarios. Complementary, we used pooled RAD sequencing to assess relations between genetic diversity on the one hand, and connectivity, habitat suitability and altitude on the other hand. Results: We show that both habitat fragmentation and climate warming reduce the amount of suitable and reachable habitat. Complete abandonment of mild grazing practices would drastically reshuffle the distribution of suitable habitat and would render most of the remaining suitable patches poorly reachable. Moreover, serial genetic founder effects observed in high-altitudinal populations of both species suggest that their dispersal rates lag behind environmental change. Main conclusions: Together, these findings corroborate the notion that habitat fragmentation, through abandonment of mild grazing practices and agricultural intensification, is the most eminent threat to the highly biodiverse semi-natural grassland ecosystems across Europe. Fighting habitat fragmentation would increase the genetic and ecological resilience of communities towards other global environmental threats.