We investigate the generality of Rapoport's rule, that is an increase of elevational range size with increasing elevation, vs. the climatic variability hypothesis, which predicts correlations between the range of variation of climatic parameters tolerated by species and the maximum seasonal variation of these parameters experienced by these species. We tested whether the elevational distributions of vascular plants and land snails along two climatically distinct transects in Lagodekhi in the Greater Caucasus, and Sairme in the Lesser Caucasus, follow these rules. The elevational range size distributions of plants and land snails in Lagodekhi and Sairme do not correspond to Rapoport's rule, but show a maximum at mid-elevations. The mean range of annual temperatures tolerated by the species that have their maximum tolerance of temperature seasonality in the same temperature seasonality category significantly increases with the maximum tolerated temperature seasonality confirming the climatic variability hypothesis. This rule was also confirmed with regard to precipitation, but precipitation had different effects along the two investigated transects. Our results suggest that the investigation of variables that directly affect the studied organisms instead of surrogate variables like elevation or latitude increases our ability to understand the distribution of biodiversity.