Format: ORAL

Sonia Merinero1, 2, Caroline Greiser2, Kristoffer Hylander2, Alicia Valds2, Johan Ehrln2

1 Universidad Rey Juan Carlos, Móstoles, Spain. 2 Stockholm University & Bolin Centre for Climate Research, Stockholm, Sweden.

Climate and biotic factors, and their complex interactions, drive species performance and distributions. Climate at the local scale (i.e. microclimate) drives population dynamics, ultimately determining local species abundance and fine-scale distribution. If populations are locally adapted to their environment, we would expect different responses to environmental change among populations across the species range. Understanding how microclimate affects biotic interactions and accounting for intraspecific variation in responses can improve our predictions of species performance and distribution. We examined the direct and indirect effects of microclimate and mollusc grazing on five distant populations of the ground-dwelling forest lichen Peltigera aphthosa. We transplanted individuals from each population to 56 boreal forest sites covering a wide microclimate gradient in central Sweden and recorded their growth for one year. We quantified the direct and indirect effects of microclimate, grazing and populations origin on lichen growth using confirmatory path analyses approaches (piecewise Structural Equation Models). We found indirect effects of microclimate and populations origin mediated by grazing: 1) lichen growth decreased with increasing grazing pressure, which was enhanced by increasing temperature and air humidity during the growing season; and 2) populations differed in their susceptibility to grazing, as one population experienced higher damage. Our study adds evidence on the importance of climate-mediated antagonistic biotic interactions. When predicting future species distributions in the face of climate change, in addition to microclimatic drivers, both the presence of natural enemies together with local population differentiation needs to be considered.