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Ecology topic #22, p. 1 of 8 Biomes 1. Definitions A. Convergence is the process by which unrelated organisms evolve a resemblance to each other in response to common environmental conditions. E.g. mangroves worldwide typically have thick, leathery leaves, root projections, vivipary B. Biome: a type of ecological community characterized by distinctive plant assemblages covering major parts of the earths surface Key points: I. Geographic distributions of biomes correspond closely to major climate zones because no single type of plant can endure the entire range of conditions on earth III. Biome types can be very uniform wherever they occur on the globe, even though they may possess different species. E.g. Rain forests or deserts in different parts of the world 3. Climatic and physical conditions are the major determinants of plant distributions A. Because heat influences moisture stress, temperature and precipitation together are the determinants of boundaries of major biomes. B. A widely adopted climatic classification is that of Heinrich Walter based on the annual course of temperature and precipitation (see text Figure 5.8) I. Recognizes 9 climate zones, from Equatorial (Tropical rain forest) to Polar (Tundra) C. A different approach: Whittaker started with vegetation structure and related it to average precipitation and temperature (see text Figure 5.9) Ecology topic #22, p. 2 of 8 I. The biomes fall in a triangular area with corners representing following warm- moist, warm-dry, or cool-dry conditions. A. Other Considerations I. Soils provide the foundation for terrestrial biomes and influence local plant distributions a. Profile provides a snapshot of soil structure in a constant state of flux. O horizon : Organic Layer freshly fallen organic material - most superficial layer. A horizon : Mixture of minerals, clay, silt and sand. B horizon : Clay, humus, and other materials leached from A horizon - often contains plant roots. C horizon : Weathered parent material. II. Fire shapes vegetation toward drier end of spectrum, typically in grassland and shrub biomes where moisture is intermediate (sufficient productivity for fuels to accumulate) and seasonal droughts occur (fuels dry out sufficiently to burn).... View Full Document

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