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BIO153 Ch 55 Notes.pdf

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Department
Biology
Course Code
BIO153H5
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Christoph Richter

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Freeman, Biological Science, 4e, Chapter 55 Chapter 55 - Biodiversity and Conservation Biology Learning Objectives: Students should be able to … • Describe the three levels at which biodiversity is quantified. • Explain the evidence supporting the notion that a mass extinction is currently occurring. • Explain how humans are dependent on biodiversity. • Discuss the various solutions to the biodiversity crisis. Lecture Outline I. What Is Biodiversity? A. Biodiversity defines all the distinctive populations and species living today—the phylogenetic tree of all organisms. B. Biodiversity can be measured and analyzed at several levels. 1. Genetic diversity—the total genetic information contained within all individuals of a species 2. Species diversity⎯the variety of life-forms on Earth a. The red panda and Indian river dolphin have few close relatives; therefore, they are species-poor lineages. (Fig. 55.1) 3. Ecosystem diversity⎯the variety of biotic communities in a region along with the abiotic components 4. Biodiversity changes through time due to mutations, speciations, extinctions. C. How many species are living today? 1. Given that only a fraction of the organisms alive have been discovered to date, how can biologists estimate the total number of species on Earth? 2. Taxon-specific surveys a. Terry Erwin and J. C. Scott used insecticidal fog to knock down species from the top of a rain forest tree called Luehea seemannii. They identified more than 900 different species of beetles among the individuals that fell. (Fig. 55.2) b. If each of the 50,000 tropical tree species harbors the same number of arthropod specialists, then the world total of arthropod species would exceed 30 million. c. Based on these types of studies, biologists estimate that there are more than 100 million species. (Box 55.1) 3. All-taxa surveys a. To obtain a more direct estimate of total species numbers, the first effort to find and catalog all forms of life present at a single site is now under way. The location is Great Smoky Mountains National Park in the southeastern United States. b. A consortium of biologists and research organizations initiated this all-taxa survey in 1998. When it is complete, in 2015, biologists will have a much better database to use in estimating the extent of biodiversity. © 2011 Pearson Education, Inc. Freeman, Biological Science, 4e, Chapter 55 II. Where is Biodiversity Highest? A. Tropical rain forests are particularly species rich. 1. They represent 7% of Earth’s land area but contain at least 50% of all species present. B. Hotspots of biodiversity and endemism 1. Biologists use the term hotspot to denote areas in the tropics that have exceptionally high species richness. a. In terms of bird species, the Andes Mountains, the Amazon River basin, portions of East Africa, and southwest China are important hotspots. (Fig. 55.3a) 2. Researchers are also interested in finding out which regions have a high proportion of endemic species⎯that is, species that are found in one area and nowhere else. (Fig. 55.3b) C. Conservation hotspots 1. Mapping species richness hotspots and centers of endemism can inspire interesting questions—principally, why certain regions contain many species or a high proportion of endemic taxa. 2. In addition, biologists are studying the geographic distribution of biodiversity as a way of focusing conservation efforts. 3. In 1999 a team set out to identify regions of the world that meet two criteria: a. They contain at least 1500 endemic plant species. b. At least 70% of their traditional or primary vegetation has been lost. 4. Although these areas cover only 2.3% of Earth’s land area, they contain more than 50% of all known plant species and 42% of all known vertebrate species. (Fig. 55.4) III. Threats to Biodiversity A. The high rate of extinction 1. Today species are vanishing faster than at virtually any other time in Earth’s history. Modern rates of extinction are 100 to 1000 times higher than the average rate recorded in the fossil record over the past 550 million years. 2. Fossil evidence on islands in the South Pacific suggests that about 2000 bird species were wiped out as people colonized this area between the years 400 and 1600. B. Changes in the nature of the problem 1. Most extinctions that have occurred during the past 1000 years took place on islands and were caused by overhunting or the introduction of exotic species—nonnative competitors, diseases, or predators. 2. Endangered species, which are almost certain to go extinct unless effective conservation programs are put in place, are now more likely to be found on continents than on islands. © 2011 Pearson Education, Inc. Freeman, Biological Science, 4e, Chapter 55 3. Invasive species are either outcompeting or directly killing native species. a. The brown tree snake was introduced to Guam and caused the extinction of dozens of bird species. (Fig. 55.5) 4. A recent analysis of 488 endangered species native to Canada reached several conclusions. (Fig. 55.6) a. Virtually all theendangered species are affected by more than one factor. b. Habitat loss is the single most important factor in the decline of these species. c. Overharvesting is the dominant problem for marine species, whereas pollution plays a larger role for freshwater species. d. Factors beyond human control can be important; background extinctions will continue to occur. 5. Overhunting has emerged recently as a dire threat to many mammal populations in Africa and southeast Asia. (Fig. 55.7) 6. Habitat destruction a. Humans cause habitat destruction by logging and burning forests, overhunting, damming rivers, dredging and trawling the oceans, plowing prairies, grazing livestock, filling in wetlands, and excavating and extracting minerals to build housing developments, golf courses, shopping centers, office complexes, airports, and roads. (Fig. 55.8) b. Satellite images of the wet tropical rain forest in Brazil made in 1984 and 2005 show extensive deforestation. (Fig. 55.9) 7. Habitat fragmentation a. Habitat fragmentation turns large, contiguous areas of natural habitats into small, isolated fragments. b. Habitat fragmentation is a big concern to biologists. (1) Habitats can be too small to support some species. (2) Fragmentation reduces the ability of some animals to disperse. (3) It creates a large amount of vulnerable edge habitat. c. When habitats are fragmented, the quality and quantity of habitat decline drastically. In addition to more than 8 million hectares of primary forest lost in South America and Africa each year, large amounts of high-quality habitat are lost to fragmentation. (Fig. 55.10) 8. Stochastic and genetic problems in small populations a. When populations are fragmented into metapopulation structure, gene flow between isolated groups is reduced or eliminated. Maintaining gene flow can aid populations in avoiding genetic problems. Example: sheep. (Fig. 55.11) b. Genetic drift is much more pronounced in small populations. © 2011 Pearson Education, Inc. Freeman, Biological Science, 4e, Chapter 55 c. Small populations become inbred, and inbreeding often leads to lowered fitness—the phenomenon known as inbreeding depression. C. How can biologists predict future extinction rates? 1. Biologists use two approaches to estimate current extinction rates and how they might change in the near future. 2. Researchers use an approach called Population Viability Analysis (PVA) to estimate the probability that a
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