Dispersal limitations determine range expansion of interacting species

Background/Question/Methods

Species community dynamics and their subsequent response to environmental change are regulated by both abiotic drivers such as habitat conditions or disturbance, and biotic mechanisms, such as dispersal and interspecific interactions. In this study, we analyze the climate change driven dynamic range shifting of two strongly interacting species: Titania's Fritillary butterfly (Boloria titania) whose larvae feed almost exclusively on the herbal plant Adderwort (Polygonum bistorta). Currently, the butterfly is present in the European Alps and the Eastern Baltic region. Statistical modeling shows that areas in Northern Europe would also be climatically suitable. However, the butterfly’s range is restricted due to climatic limitations of its host plant. Projections under climate change indicate that Northern European areas become climatically suitable for both species in future. But, can the two species follow the shifting climatic conditions? With a metapopulation-analogous model for two interacting species, we simulate the range shifting dynamics of this host plant – butterfly interaction. We analyze how the two biotic mechanisms dispersal and trophic dependence affect the species’ response to climate change.

Results/Conclusions

Although large scale distribution data for both species are limited, model calibration is surprisingly successful in selecting suitable parameter ranges for the extinction and colonization processes. Particularly, expert knowledge on dispersal limitations of the species is confirmed. Our analysis of the range shifting dynamics of these two interacting species reveals major bottlenecks for the Northwards range expansion of the butterfly. A geographical barrier of climatically unsuitable area separates butterfly populations from potentially suitable areas in the North. With realistic dispersal, the chance is small for the butterfly to traverse the barrier. In future, even if the butterfly can establish in Northern Europe, its range expansion might be limited by colonization abilities of both species.