Latitudinal pattern of between-altitude faunal similarity: mountains might be "higher" in the tropics

Abstract

Moving up or down a mountain from a given site, one encounters faunas that differ by varying degrees. The elevational separation between sites obviously influences the magnitude of that difference (faunal similarity is inversely proportional to elevational separation); local environmental discontinuities, steepness of slope (Beals 1969), and certain global factors may also affect these “between-altitude” faunal similarities. Here I examine one possible global relationship, that of latitude and the extent of faunal similarity for reptilian and amphibian communities at different altitudes. I gathered these data to test Janzen’s (1967) hypothesis that mountains are effectively “higher” to animals in the tropics; if this is true, then “between-altitude” faunal similarity should vary directly with latitude.