These studies were motivated by a resurgence in interest in how the geographic ranges in terrestrial taxa correlate with latitudinal trends in species richness. Curiously enough, the history of science often proceeds in a reverse order from expectations and this is very true in biogeography. Patterns on islands , of species diversity , and of tropical communities are already clear and even moderately well understood while patterns of single species' ranges still seem to be catalogs of special cases. Patterns in the distribution of species. Schematic representation of the geometric constraint model.
Black circles represent species' mean depth of occurrence.
The upper panel shows species mean depth of occurrence and their vertical range. It is shown how the vertical range is determined by the proximity of a boundary. The vertical range is equal to 2 times the distance of the species Md to the closest barrier. The lower panels are a schematic representation of the relationship between the VR and Md . The shaded triangle represents tje constraint envelope for Vr - Md values.