Microgeography, Not Just Latitude, Drives Climate Overlap on Mountains from Tropical to Polar Ecosystems.

AbstractAn extension of the climate variability hypothesis is that relatively stable climate, such as that of the tropics, induces distinct thermal bands across elevation that render dispersal over tropical mountains difficult compared with temperate mountains. Yet ecosystems are not thermally static in space-time, especially at small scales, which might render some mountains greater thermal isolators than others. Here we provide an extensive investigation of temperature drivers from fine to coarse scales, and we demonstrate that the degree of similarity in temperatures at high and low elevations on mountains is driven by more than just absolute mountain height and latitude. We compiled a database of 29 mountains spanning six continents to characterize thermal overlap by vertically stratified microhabitats and biomes and owing to seasonal changes in foliage, demonstrating via mixed effects modeling that micro- and mesogeography more strongly influence thermal overlap than macrogeography. Impressively, an increase of 1 m of vertical microhabitat height generates an increase in overlap equivalent to a 5.26° change in latitude. In addition, forested mountains have reduced thermal overlap-149% lower-relative to nonforested mountains. We provide evidence in support of a climate hypothesis that emphasizes microgeography as a determinant of dispersal, demographics, and behavior, thereby refining the classical theory of macroclimate variability as a prominent driver of biogeography.