study of the geographic distribution of plants and animals. It is concerned not only with habitation patterns but also with the factors responsible for variations in distribution.

Strictly speaking, biogeography is a branch of biology, but physical geographers have made important contributions, particularly in the study of flora. The classification of vegetation and the preparation of maps of vegetation have been notably advanced by F. Shreve, H.L. Shantz, H.M. Raup, and others.

Biogeographic studies divide the Earth's surface—primarily the continents and islands—into regions exhibiting differences in the average composition of flora and fauna. It is thought that the present-day distribution patterns of plant and animal forms, as reflected in such biogeographic regions, are the result of many historical and current causes. These causes include present climatic and geographic conditions, the geologic history of the landmasses and their climates, and the evolution of the taxon (e.g., genus or species) involved. Investigators have found that rate of dispersal, adaptability to prevailing environmental conditions, and the age of the taxa being studied also have a significant impact on pattern and extent of distribution.