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Biogeography is the scientific study of the distribution and diversity of organisms on Earth. “Distribution” is simply where organisms are found. “Diversity,” however, has multiple facets, which we will explore in more detail in Chapter 56, but for now you can think of it simply as the number and composition of species or higher taxa. For centuries, the processes that control these biogeographic patterns have puzzled naturalists. Why do species vary in their distributions around Earth, and what controls this variability?
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Biomes cross continents, occurring where climatic conditions are similar. Earth’s major biomes include tropical rainforests, deserts, temperate grasslands, temperate deciduous forests, temperate evergreen forests, boreal forests, and tundra.
Alfred Russel Wallace observed distributional differences in biota on the Malay Archipelago that led to his theory of biogeography.
Hypotheses to explain the causes of latitudinal variations in diversity include species diversification rate, species diversification time, and productivity.