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Chap. 3 Extinction
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  1. Chap. 3 Extinction 鄭先祐 生態主張者 Ayo Japalura@hotmail.com

  2. Chap. 3 Extinction • Rate of extinction • Causes of extinction • Risks confronted by endangered species • Characteristics of species and their relationship to extinction 生態學 2003 Chap.3 Extinction

  3. 3.1 The Extinction Crisis • Extinction • All individuals die without producing progeny • Pseudoextinction • Species disappear over evolutionary time • Lineage transformed into separate lineages • Fossil Record • Extinct species to living species – 1,000:1 生態學 2003 Chap.3 Extinction

  4. Fossil Record • Average life span of a species – 4 million years • Average extinction rate – 2.5 species per year • Total number of species over time – 10 million • Favors successful, geographically wide-ranging species • Biased toward vertebrates and mollusks • Background extinction rates are probably higher than indicated in fossil record. • Example Extinction rates 10 times higher than predicted by fossil record 生態學 2003 Chap.3 Extinction

  5. Effects due to humans – Distant Past • Correlation between human population growth and the number of extinctions (Figure 3.1) • Large scale extinctions in North and South America coinciding with the arrival of humans (11 thousand years ago) • North America lost 73% of its genera of large mammals • South America lost 80% of its genera of large mammals 生態學 2003 Chap.3 Extinction

  6. 6 5 50 4 Birds 40 Mammals Number of humans (billions) 3 Number of extinct species 30 2 20 1 10 0 0 1650 1700 1750 1800 1850 1900 1950 2000 1600-1700 1700-1800 1800-1900 1900-2000 Year Year Fig. 3.1 Population growth and animal extinctions. (left) Geometric increase in the human population.(right) increasing numbers of extinctions in birds and mammals. 生態學 2003 Chap.3 Extinction

  7. Effects due to humans – Distant Past • Large scale extinctions in Australia coinciding with the arrival of humans (13 thousand years ago) • Lost nearly all of its large mammals, giant snakes, and reptiles • Nearly half of its large flightless birds • Probable causes of these extinctions • Hunting • Some climate change 生態學 2003 Chap.3 Extinction

  8. Effects due to humans – Recent Past • Devastating effects on islands • Hawaii – 4th and 5th century Polynesians arrived • Exterminated 50 out of 100 species of endemic land birds. • New Zealand – End of the 18th century • Entire avian megafauna consisting of huge land birds was exterminated • Accomplished through hunting and habitat destruction 生態學 2003 Chap.3 Extinction

  9. Devastating effects on islands • Madagascar – last 1,500 years • Exterminated Giant elephant bird, largest bird ever recorded • 20 species of lemur, most larger than any surviving species • 2 giant land tortoises 生態學 2003 Chap.3 Extinction

  10. 3.2 Patterns of Extinction • Islands vs. continental areas (Table 3.1) • Reasons for differences in extinction rate • Island species may consist of a single population • Single climatic event can lead to extinction • Island species may have evolved in the absence of terrestrial predators • Characteristics contributing to extinction • Flightlessness • Tameness • Reduced reproductive rates • Ex. Hawaii (Figure 3.2) • Causes of extinction (Figure 3.3) 生態學 2003 Chap.3 Extinction

  11. 生態學 2003 Chap.3 Extinction

  12. 100 Habitat loss Exotic species 75 Pollution Percent endangered Hunting 50 Disease 25 0 Hawaiian Birds Continental U.S. plants Hawaiian plants Continental U.S. birds Fig. 3.2 生態學 2003 Chap.3 Extinction

  13. No cause assigned 56% 17% Introduced animals Habitat destruction 16% Hunting 10% Fig. 3.3 The causes of extinctions 1% Other causes 生態學 2003 Chap.3 Extinction

  14. Introduced species effects • Competition • Not been shown to eliminate an entire species • Predation • Rats, cats, and mongooses have accounted for at least 112 of 258 extinctions of birds on islands (43%). • Disease and parasitism • Avain malaria in Hawaii accounted for the loss of 50% of the local Hawaiian bird species 生態學 2003 Chap.3 Extinction

  15. Habitat destruction • A prime cause of extinction • Ex. Deforestation • Subtle alterations (e.g. pollution) have not yet been shown to cause extinction • Direct exploitation –Hunting • Caused numerous extinctions • Ex. Figure 3.4 生態學 2003 Chap.3 Extinction

  16. (a) Steller’s sea cow (b) the dodo Fig 3.4 (d) the Carolina parakeet (c) the passenger pigeon 生態學 2003 Chap.3 Extinction

  17. 3.3 Endangered Species • Definition – a species that is thought to be at risk of extinction in the foreseeable future. • Factors threatening species with Extinction • Habitat loss or modification • Hunting • Accidental or deliberate introduction of exotic species • 被認定為害蟲。譬如:野狼和老虎 • Incidental takes, 譬如:混獲 (捕撈) • Disease, both exotic and endemic 生態學 2003 Chap.3 Extinction

  18. Characteristics of Factors • Human in origin • Species are threatened with several factors simultaneously • Ex. Threats facing terrestrial mammals in Australia and the Americas • 119 species considered endangered • 75% threatened by more than one factor • 27 species face four or more threats • Major threat – 76% of the species are experiencing habitat loss or modification (Figure 3.5) 生態學 2003 Chap.3 Extinction

  19. Threat and classes of threats Percent of species affected 0 10 20 30 40 50 60 Habitat loss & modification: 76% Cultivation & settlement Pastoral development Logging & plantations Other Exploitation: 50% Meat Fur and hides Live trade Introductions: 18% Predators Competitors Others Limited distribution Persecution Fig. 3.5 The factors that threaten mammals in Australia and the Americas. Disturbance Incidental take Disease 生態學 2003 Chap.3 Extinction

  20. Overexploitation • Significance of hunting – Valuable fur and wood (Figure 3.6) • Overexploitation • Overharvesting for commercial interests • Rare plants are threatened by collectors 生態學 2003 Chap.3 Extinction

  21. Five categories • Habitat destruction • Alien species • Over-harvesting • Disease (both native and alien) • Pollution David Wilcove (1998) categorized threats to plants and animals in the US. 生態學 2003 Chap.3 Extinction

  22. Endangered Species • Sample size: 1880 species (Figure 3.7) • Habitat degradation was by far the most important threat (threatening 85% of species). • Overall, pollution threatens 46% of vertebrates and 45% of invertebrates, and of minor importance only for plants (7%). • Overexploitation of mammals, birds, and reptiles is considerable. 生態學 2003 Chap.3 Extinction

  23. Percent of species threatened 0 10 20 30 40 50 60 70 80 90 100 All species Vertebrates Invertebrates Plants Mammals Birds Reptiles Amphibians Fish Freshwater mussels Butterflies Other invertebrates Fig. 3-7 生態學 2003 Chap.3 Extinction Habitat loss Exotic species Pollution Over exploitation Disease

  24. Endangered Species • Categorization of threats by class of species (Figure 3.8) • Mammals are clearly the most endangered taxonomic group. • Categorization of threats by geographic areas (Table 3.2) • The majority of threatened mammals occur in tropical countries • Tropical countries have more species (therefore should have more endangered species • Tropical countries have a higher percentage of endangered species as well. 生態學 2003 Chap.3 Extinction

  25. Percentage endangered 1 1.5 2 2.5 3 3.5 0 0.5 Mammals Fish Birds Reptiles Amphibians All invertebrates Fig. 3.8 Percentage of Known species classed as endangered. 生態學 2003 Chap.3 Extinction

  26. 生態學 2003 Chap.3 Extinction

  27. Endangered Species • Bigger countries have more endangered species than smaller countries (Figure 3.9) • US and endangered reptiles, amphibians, and fishes • Better monitoring and documenting activities 生態學 2003 Chap.3 Extinction

  28. 60 55 Madagascar Indonesia 50 45 Brazil India 40 China Number of threatened mammals Australia 35 Tanzania Zaire 30 Peru United States Vietnam Cameroon Colombia 25 Mexico Thailand South Africa Nigeria Laos Argentina 20 10,000 20,000 50,000 100,000 500,000 1,000,000 2,000,000 200,000 Country area (1000 ha) Fig. 3.9 Relationship between number of threatened species and area of a country. 生態學 2003 Chap.3 Extinction

  29. Correlations between human factors and extinction • 1995, Kerr and Currie Compared 90 countries • Six indices of human activities (Table 3.3) • Human population explained the most variation in the proportion of endangered species of birds. • Per capita GNP explained the most variation in mammals 生態學 2003 Chap.3 Extinction

  30. 生態學 2003 Chap.3 Extinction

  31. 3.4 Species Characteristics and Extinction • Rarity (Fig. 3.10) • Determined by Geographic range, Breadth of habitat, Local population size • Ability to disperse (Fig. 3.10) • Rescuing a population through immigration • Degree of specialization (Fig. 3.10) • Organisms that are specialized are more likely to become extinct • Limited food • Limited habitat 生態學 2003 Chap.3 Extinction

  32. Less prone to extinction More prone to extinction Common 1) Rarity Rare N N t t 2) Dispersal ability Poor dispersal Good dispersal Habitat destroyed Habitat destroyed Not able to reach new fragment Can reach new fragment Habitat fragments Habitat fragments 3) Degree of specialization High specialization Low specialization Fig. 3.10a 生態學 2003 Chap.3 Extinction

  33. Population variability (Fig. 3.10) • Stable populations are less likely to go extinct • Trophic status (Fig. 3.10) • Applies to animals only • Higher trophic levels more at risk • Life span (Fig. 3.10) • Reproductive ability (Fig. 3.10) 生態學 2003 Chap.3 Extinction

  34. Less prone to extinction More prone to extinction 4) Population variability Low variability High variability Population size relatively constant: extinction unlikely Sudden population decline can lead to extinction N N 5) Trophic status t t High trophic status Low trophic status Pyramid of numbers Top carnivores Carnivores - tens Herbivores - hundreds Plants - thousands Fig. 3.10b Characteristic that make species particularly vulnerable to extinction. 生態學 2003 Chap.3 Extinction

  35. More prone to extinction Less prone to extinction Long life span Short life span 6) Life span 7) Reproductive ability High reproductive ability Low reproductive ability Fig. 3.10c Characteristic that make species particularly vulnerable to extinction. 生態學 2003 Chap.3 Extinction

  36. 問題與討論! Japalura@hotmail.com Ayo 台南站: http://mail.nutn.edu.tw/~hycheng/ 生態學 2003 Chap.3 Extinction