1. The study of the distribution of different species of organisms around the planet and the factors that influenced that distribution. (biology-online.org)
2. The branch of biology concerned with the geographical distribution of plants and animals. (Collins English Dictionary – Complete and Unabridged © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003)
3. The scientific study of the geographic distribution of plant and animal life. Factors affecting distribution include the geologic history of a region, its climate and soil composition, and the presence or absence of natural barriers like deserts, oceans, and mountains. Biotic factors such as interactions among competing species, coevolutionary influences, and the reproductive and nutritional requirements of populations and species are also studied.
A biogeographic region is a large, generally continuous division of the Earth’s surface having a distinctive biotic community. Biogeographic regions are usually defined separately for floral and faunal communities and are largely restricted to the terrestrial areas of the Earth. (The American Heritage® Science Dictionary Copyright © 2005 by Houghton Mifflin Company. Published by Houghton Mifflin Company.)