Page 678 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

642 part IV Soils, Ecosystems, and Biomes
The patterns of species distributions on Earth are important subjects of biogeography. Earth’s bio- diversity is spread unevenly across the planet and is related to geology, climate, and the evolutionary history of particular species and species assemblages. The branch of biogeography that is concerned with the past and present distributions of animals is called zoogeography; the corresponding branch for plants is phytogeography.
Plant and animal communities are commonly grouped into biomes, also known as ecoregions, rep- resenting the major ecosystems of Earth. A biome is a large, stable community of plants and animals whose boundaries are closely linked to climate. Ideally, biomes are defined by mature, natural vegetation; however, most of Earth’s biomes have been affected by human activities, and many are now experiencing accelerated rates of change that could produce dramatic alterations in the biosphere within our lifetime.
Biogeographic Realms
The recognition that distinct regions of broadly similar flora (plants) and fauna (animals) exist was the earliest beginning of biogeography as a discipline. (Flora and fauna are general terms for the typical collections of animals and plants throughout a region or ecosystem.) A biogeographic realm (sometimes called an ecozone) is a geographic region where a group of associated plant and animal species evolved. Alfred Wallace (1823–1913), the first scholar of zoogeography, developed a map de- lineating six zoogeographical regions in 1860, building on earlier work by others regarding bird distributions (Figure 20.1a). Wallace’s realms correspond generally to the continental plates, although Wallace knew nothing of the theory of plate tectonics at the time. Biogeographic realms were also developed based on plant associations and modified over time, resulting in the similar though
In this chapter: We begin with a discussion of Earth’s biogeographic realms, the broadest groupings of species. We then exam-
ine biomes, explaining the basis for
their classification and consider-
ing invasive species and their
impacts on plant and animal
communities within biomes. Tropic of Cancer The bulk of this chapter 20°
120°
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Palearctic
explores Earth’s 10 major terrestrial biomes, including their location, community structure, and sensitivity to human impacts. Table 20.1 summarizes the connections between vegetation, climate, soils, and water-budget char- acteristics for each biome.
Biogeographic Divisions
Earth’s biosphere can be di- vided geographically based on assemblages of similar plant and animal communi- ties. One class of geographic division—the biogeographic region, or realm—is deter- mined by species distribu- tions and their evolutionary history. Another class—the biome—is based on plant communities; it is deter- mined mainly by vegetation life form and community characteristics as they relate to climate and soils.
Ethiopian Neotropical ATLANTIC
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(a) The six animal realms as defined by biogeographer Alfred Wallace in 1860.
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(b) The eight realms in use today, based on plant and animal associations and evolution.
▲Figure 20.1 Biogeographic realms. [(b) After Olsen, et al., “Terrestrial Ecoregions of the World: A New Map of life on Earth,” Bioscience 51:933–938 (2004); modified by UNEP/WCMC, 2011.]
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ROBINSON PROJECTION
Australasian
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