Do interlinks between geography and ecology explain the latitudinal diversity patterns in Sciuridae? An approach at the genus level

Abstract

The latitudinal gradient theory explains the uneven distribution of taxa richness across the world. We explore this theory using genera of Sciuridae (Mammalia: Rodentia). Distribution data for each genus were obtained from literature and mapped with the WorldMap program. The two hemispheres were subdivided into 23 latitudinal bands of equal area. As the total number of genera in each latitudinal band was influenced by the different available area, data were normalized prior to analyses. Then, genera density of each latitudinal band was correlated with latitude, and the ratio of genera richness of each guild to total genera richness was calculated for each latitudinal band. Total genus density was significantly correlated with flying squirrel density and terrestrial squirrel density in both hemispheres, and these two genera densities were significantly correlated with each other in the northern hemisphere. The guilds showed clear vicariance patterns. The total diversity of genera of Sciuridae was inversely correlated to latitude. The increase of genera towards tropical northern hemisphere was due to the progressive increase of the tree and flying squirrel genera. Change in biomes (tundra vs. forests) is likely responsible for the increase in the tree squirrel component at these latitudes. Overall, our study confirmed assumptions of the latitudinal gradient theory.