Vertical Zonation of Land Snails in the Iraqi Slopes of the Persian Mountains and in the Rocky Mountains of Alberta, Canada^∗

Abstract

The problems of determining altitudinal variations in molluscan fauna and relating them to climate on the Iraqi slopes of the Persian mountains and in the Rocky Mountains of Alberta are compared. Iraq is a small deforested area whereas the Rocky Mountains of Alberta have undergone partial and temporary deforestation by fire. Both areas support molluscs but the number of species present has been drastically reduced in Iraq. The common species in Iraq permit an identification of distinctive zones which parallel the isohyets. Due to its size, mapping of the distribution of molluscs is barely possible in Alberta; therefore traverses must be used. The mollusc distribution pattern is similar, but there is an extensive region in the upper Hudsonian zone that lacks molluscs, even though the ground in winter is much warmer, due to snow cover, than on the prairie. But the first snow temperatures suggest that a very cold blanket is formed on the ground inhibiting molluscs in the evergreen forest. Distribution of aspen (Populus tremuloides) and grasses affects the distribution of some species, while Gastrocopta pentodon appears to be a relict from the Altithermal period and has survived at suitable locations. In both areas, the molluscs can be used as climatic and vegetational indicators.