chap. 3 extinction 鄭先祐 生態主張者 ayo japalura@hotmail.com
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Chap. 3 Extinction
鄭先祐生態主張者 Ayo
Japalura@hotmail.com
2003 Chap.3 Extinction生態學 2
Chap. 3 Extinction
1. Rate of extinction
2. Causes of extinction
3. Risks confronted by endangered species
4. Characteristics of species and their relationship to extinction
2003 Chap.3 Extinction生態學 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
2003 Chap.3 Extinction生態學 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
2003 Chap.3 Extinction生態學 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
2003 Chap.3 Extinction生態學 6
Num
ber
of
hum
ans
(bill
ions)
0
1
2
3
4
5
6
1650 1700 1750 1800 1850 1900 1950 2000 1600-1700 1700-1800 1800-1900 1900-2000
Birds
Mammals
Num
ber
of
exti
nct
speci
es
0
10
20
30
40
50
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.
2003 Chap.3 Extinction生態學 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
2003 Chap.3 Extinction生態學 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 l
and birds.
• New Zealand – End of the 18th century– Entire avian megafauna consisting of huge land
birds was exterminated
– Accomplished through hunting and habitat destruction
2003 Chap.3 Extinction生態學 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
2003 Chap.3 Extinction生態學 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)
2003 Chap.3 Extinction生態學 11
2003 Chap.3 Extinction生態學 12
Perc
ent
endangere
d
0
25
50
75
100Habitat loss
Exotic species
Pollution
Hunting
Disease
Continental U.S. birds
HawaiianBirds
ContinentalU.S. plants
Hawaiianplants
Fig. 3.2
2003 Chap.3 Extinction生態學 13
No cause assigned
Introduced animals
Habitat destruction
Hunting
Other causes
56%
17%
16%
10%
1%Fig. 3.3 The causes of extinctions
2003 Chap.3 Extinction生態學 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
2003 Chap.3 Extinction生態學 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
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Fig 3.4
(a) Steller’s sea cow (b) the dodo
(c) the passenger pigeon •(d) the Carolina parakeet
2003 Chap.3 Extinction生態學 17
3.3 Endangered Species• Definition – a species that is thought to be at ri
sk of extinction in the foreseeable future.
• Factors threatening species with Extinction
1. Habitat loss or modification
2. Hunting
3. Accidental or deliberate introduction of exotic species
4. 被認定為害蟲。譬如:野狼和老虎5. Incidental takes, 譬如:混獲 ( 捕撈 )
6. Disease, both exotic and endemic
2003 Chap.3 Extinction生態學 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)
2003 Chap.3 Extinction生態學 19
Threat and classes of threats Percent of species affected
0 10 20 30 40 50 60Habitat loss & modification: 76%
Cultivation & settlement
Pastoral development
Logging & plantations
OtherExploitation: 50%
Meat
Fur and hides
Live trade
Predators
Competitors
Limited distribution
Persecution
Disturbance
Incidental take
Disease
Introductions: 18%
Others
Fig. 3.5 The factors that threaten mammals in Australia and the Americas.
2003 Chap.3 Extinction生態學 20
Overexploitation
• Significance of hunting – Valuable fur and wood (Figure 3.6)
• Overexploitation
– Overharvesting for commercial interests
– Rare plants are threatened by collectors
2003 Chap.3 Extinction生態學 21
Five categories
1. Habitat destruction
2. Alien species
3. Over-harvesting
4. Disease (both native and alien)
5. Pollution
David Wilcove (1998) categorized threats to plants and animals in the US.
2003 Chap.3 Extinction生態學 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.
2003 Chap.3 Extinction生態學 23
All species
Percent of species threatened0 10 20 30 40 50 7060 80 90 100
Habitat loss Exotic species Pollution Over exploitation Disease
Invertebrates
Vertebrates
Plants
Mammals
Birds
Reptiles
Amphibians
Fish
Freshwater mussels
Butterflies
Other invertebrates
Fig. 3-7
2003 Chap.3 Extinction生態學 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.
2003 Chap.3 Extinction生態學 25
Percentage endangered
0 0.5 1 1.5 2 2.5 3 3.5
Mammals
Fish
Birds
Reptiles
Amphibians
All invertebrates
Fig. 3.8 Percentage of Known species classed as endangered.
2003 Chap.3 Extinction生態學 26
2003 Chap.3 Extinction生態學 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
2003 Chap.3 Extinction生態學 28
20
25
30
35
40
45
50
55
60
Num
ber
of
thre
ate
ned m
am
mals
10,000 20,000 50,000 100,000 200,000 500,000 1,000,000 2,000,000
MadagascarIndonesia
IndiaBrazil
ChinaAustralia
Zaire
United States
Argentina
MexicoSouth AfricaNigeria
Thailand
Laos
Vietnam Cameroon
Tanzania
Peru
Colombia
Country area (1000 ha)
Fig. 3.9 Relationship between number of threatened species and area of a country.
2003 Chap.3 Extinction生態學 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
2003 Chap.3 Extinction生態學 30
2003 Chap.3 Extinction生態學 31
3.4 Species Characteristics and Extinction
1. Rarity (Fig. 3.10)• Determined by Geographic range, Breadth of
habitat, Local population size
2. Ability to disperse (Fig. 3.10)• Rescuing a population through immigration
3. Degree of specialization (Fig. 3.10)• Organisms that are specialized are more likely to
become extinct
• Limited food
• Limited habitat
2003 Chap.3 Extinction生態學 32
Rare
Common
Poor dispersal Good dispersal
Habitat destroyed Habitat destroyed
More prone to extinction Less prone to extinction
N N
t t
Can reach newfragment
Not able to reach new fragment
High specialization Low specialization
Habitat fragments Habitat fragments
3) Degree of specialization
2) Dispersal ability
1) Rarity
Fig. 3.10a
2003 Chap.3 Extinction生態學 33
4. Population variability (Fig. 3.10)– Stable populations are less likely to go extinct
5. Trophic status (Fig. 3.10)• Applies to animals only
• Higher trophic levels more at risk
6. Life span (Fig. 3.10)
7. Reproductive ability (Fig. 3.10)
2003 Chap.3 Extinction生態學 34
Sudden population decline can lead to extinction
Population size relatively constant: extinction unlikely
Pyramid of numbers
High trophic status
N N
t t
Low trophic status
More prone to extinction Less prone to extinction
Low variabilityHigh variability
4) Population variability
5) Trophic status
Plants - thousands
Herbivores - hundreds
Carnivores - tens
Top carnivores
Fig. 3.10b Characteristic that make species particularly vulnerable to extinction.
2003 Chap.3 Extinction生態學 35
More prone to extinction Less prone to extinction
6) Life span Short life span Long life span
7) Reproductive ability
High reproductive ability Low reproductive ability
Fig. 3.10c Characteristic that make species particularly vulnerable to extinction.
2003 Chap.3 Extinction生態學 36
問題與討論!
Japalura@hotmail.com
Ayo 台南站: http://mail.nutn.edu.tw/~hycheng/
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