Macro- and microclimate interactively shape species diversity of multiple taxa in mountain landscapes

Macroclimate is a key driver of biodiversity, but habitat conditions can modulate the local microclimate by amplifying or buffering macroclimatic temperatures. The interplay between microclimatic modulation and macroclimatic temperature is crucial for shaping local biodiversity in a warming world, but remains poorly understood across life forms. We examined how macroclimate and microclimatic modulation jointly shape alpha diversity across eight taxonomic groups. We surveyed multi-taxon biodiversity along gradients of macroclimate (elevation) and microclimatic modulation (habitat structure), focusing on soil bacteria, soil fungi, understory plants, ground-dwelling arthropods, moths, flying insects, bats, and birds. We hypothesized that alpha diversity would increase with temperature at both macro- and microclimatic scales, with strongest effects for immobile and ectothermic groups, and that microclimatic effects would be more pronounced in thermally constrained (cold) macroclimates. Contrary to our expectations, micro- and macroclimatic effects were weakest for soil bacteria, soil fungi, and vascular plants, which responded more strongly to edaphic factors. Alpha diversity increased with macroclimatic temperature for arthropods, but not for the other groups. Effects of microclimatic amplification varied across taxa, with positive effects for flying insects and bats, but negative effects for soil bacteria and fungi. Interactive effects of microclimatic modulation and macroclimatic temperature for understory plants, ground-dwelling arthropods, moths, and birds indicated that microclimate influenced diversity differently in warm versus cold macroclimates. However, we found both stronger (ground-dwelling arthropods and moths) and weaker (understory plants and birds) positive effects of microclimatic amplification under cold compared to warm macroclimates. Our findings demonstrate that effects of microclimatic modulation on biodiversity depend on macroclimatic context and differ between taxa, and thus, both have to be considered when predicting climate-change impacts on biodiversity. Conservation planning should account for potentially changing effects of microclimatic modulation under climate warming that might affect the role of climatic microrefugia within the landscape.

Methods
We conducted a multi-taxon biodiversity survey along orthogonal gradients of macroclimate (i.e., elevation) and microclimatic modulation (associated with a series of habitat types from sparsely vegetated to closed forest) at Berchtesgaden National Park. We then used Hill numbers and Generalized Additive Models to study the interactive effects of macroclimatic mean summer temperature and microclimatic modulation (i.e., buffering/amplification of ambient temperatures) on alpha diversity of taxa with different thermoregulatory strategies.

For details, see the Methods section and Supporting Information of the related article.