《biology》18_Lecture.ppt

18.4 How Many Species Exist? It is estimated that 7 million to 10 million species may exist Between 7,000 and 10,000 new species are identified annually, mostly in the Tropics Tropical rainforests are believed to be home to two-thirds of the world’s existing species, most of which have yet to be named 18.4 How Many Species Exist? Although 5,000 species of prokaryote have been named, scientists discovered 4,000 different species of bacteria in a single soil sample, and an equal number in a sample of marine sediments They considered a bacterium to be a different species if its DNA differed by 30 percent from other bacteria in the sample 18.4 How Many Species Exist? Factors other than actual abundance influence whether species are discovered and named Size Ease of classification Accessibility The number of researchers searching for them 18.4 How Many Species Exist? Because tropical rainforests are being destroyed so rapidly, species may become extinct before we even know they exist The unexplored continent of the deep-sea floor may have hundreds of thousands of unknown species to be discovered The Black-Faced Lion Tamarin Fig. 18-8 Discovered in 1990 Copyright ? 2011 Pearson Education Inc. Biology: Life on Earth, 9e Lecture Outlines by Gregory Ahearn, University of North Florida Copyright ? 2011 Pearson Education Inc. Chapter 18 Systematics: Seeking Order Amidst Diversity Chapter 18 At a Glance 18.1 How Are Organisms Named and Classified? 18.2 What Are the Domains of Life? 18.3 Why Do Classifications Change? 18.4 How Many Species Exist? 18.1 How Are Organisms Named and Classified? The branch of biology that is concerned with naming and classifying organisms is known as taxonomy(分类学) Modern taxonomy was established by the Swedish naturalist Carl von Linne (1707–1778), who called himself Carolus Linnaeus Linnaeus introduced the two-part scientific name to all organisms 18.1 How Are Organisms Named and Classified? The two-part scien