LEARNING OBJECTIVES
If we are to conserve biological diversity, we must understand the large-scale, global patterns of biogeography. After reading this chapter, you should understand:
• How large-scale global patterns and the environment affect biological diversity.
• How climate, bedrock, soils, and the geography of life are related to one another.
• What biotic provinces and biomes are, and how they differ.
• How plate tectonics affects biogeography.
• What island biogeography is, and what it implies for the general geography of life, especially the geography of biological diversity.
• What the major patterns in the distribution of biomes on Earth are and the major characteristics of each of the 17 biomes found on Earth.
• How people affect the geography of life.
• How the introduction of exotic species into new habitats typically affects the new habitats.
Summary
• To conserve biological diversity, we must understand the large-scale global patterns of life. This is known as biogeography.
• Geographic isolation leads to the evolution of new species. Wallace’s realms, or biotic provinces, are major geographic divisions (generally continents) based on fundamental features of the species found in them. Species filling specific niches within one realm are of different stock from those filling the same niches in other realms.
• The rule of climatic similarity holds that similar environments lead to the evolution of biota and biological communities similar in external form and function but not in genetic heritage or internal makeup. Areas of climatic similarity with similar biota are known as biomes. A biome is a kind of ecosystem; examples are desert, grasslands, and rain forest.
• Convergent evolution occurs when two genetically dissimilar species that inhabit geographically separate parts of a biome develop along similar lines and have similar external form and function. Divergent evolution occurs when several species evolve from a common ancestral species but develop separately because of geographic isolation.
• The study of island life has led to a theory of island biogeography that includes several important concepts. One is that islands have fewer species than mainlands because of their smaller size and distance from the mainland. Another is that the smaller an island and the farther it is from the mainland, the fewer species the island will contain.
• Ecological islands—habitats separated from the main part of a biome—show the same diversity characteristics as physical islands. The smaller the ecological island and the greater its distance from its “mainland,” the fewer species it can support.
• Earth has 17 major biomes, each with its own characteristic dominant shapes and forms of life. Biomes vary in their importance to people, and some are of great importance. Most biomes have been heavily altered by human actions. Understanding the major characteristics of these biomes is important to the conservation and sustainable use of their resources.
• People have long introduced exotic species into new habitats, sometimes creating benefits, often causing new problems. From the study of biogeography, certain general rules can be set down concerning the introduction of exotic species. The primary rule is this: Unless there is a very clear and good reason to introduce an exotic species into a new habitat, don’t do it; and take precautions to prevent such introductions from occurring inadvertently.