Does elevational range-size (ERR) slope inform the idea that mountain passes are higher in the tropics?
Long-term stability of environmental conditions, inferred via adjacency to the equator as well as location along an elevational gradient, facilitates not only ecological niche specialization but also determines relative shifts in average range-sizes. Our results support the idea that “mountain passes are higher in the tropics” as indicated by differences in ERR slopes for species-rich families with greater affiliation to lowland tropical of Sundaland, as compared to places with either contemporary, or historic, variability of conditions, such as for flora noted with either montane or Sahul affiliation.