Download Chap. 3 Extinction

Chap. 3 Extinction
鄭先祐
生態主張者 Ayo
[email protected]
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
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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
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• 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 wideranging 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
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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
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5
Number of extinct species
Number of humans (billions)
6
4
3
2
1
50
Birds
40
Mammals
30
20
10
0
0
1650 1700 1750 1800 1850 1900 1950 2000
Year
1600-1700 1700-1800 1800-1900 1900-2000
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.
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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
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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
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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
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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)
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100
Percent endangered
Habitat loss
Exotic species
75
Pollution
Hunting
50
Disease
25
0
Continental
U.S. birds
Hawaiian
Birds
Continental
U.S. plants
Hawaiian
plants
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Fig. 3.2
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No cause assigned
56%
Introduced animals
17%
Habitat destruction
16%
Hunting
Other causes
10%
1%
Fig. 3.3 The causes
of extinctions
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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
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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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(a) Steller’s sea cow
(b) the dodo
Fig 3.4
(c) the passenger pigeon
•(d) the Carolina parakeet
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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
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
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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)
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Threat and classes of threats
Percent of species affected
Habitat loss & modification: 76%
0
10
20
30
40
50
60
Cultivation & settlement
Pastoral development
Logging & plantations
Exploitation: 50%
Other
Meat
Fur and hides
Live trade
Introductions: 18%
Others
Predators
Competitors
Limited distribution
Persecution
Fig. 3.5 The factors that
threaten mammals in
Incidental take
Australia and the
Disease
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Disturbance
Overexploitation
• Significance of hunting – Valuable fur and
wood (Figure 3.6)
• Overexploitation
– Overharvesting for commercial interests
– Rare plants are threatened by collectors
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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.
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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.
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0
10
Percent of species threatened
20 30 40 50 60 70 80 90 100
All species
Vertebrates
Invertebrates
Plants
Mammals
Birds
Reptiles
Amphibians
Fish
Freshwater mussels
Butterflies
Other invertebrates
Habitat loss
Exotic
species
Pollution
Over exploitation Disease
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Extinction
Fig. 3-723
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.
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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.
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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
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60
55
50
Madagascar
Indonesia
45
India
40
Brazil
Australia
35
Tanzania
30
Vietnam
25
Laos
Cameroon
Peru
China
Zaire
United States
Colombia
Mexico
Thailand
Nigeria South Africa
Argentina
20
10,000
20,000
50,000
100,000
200,000
500,000 1,000,000 2,000,000
Country area (1000 ha)
Fig. 3.9 Relationship between number of threatened species and
area of a country.
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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
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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
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Less prone to extinction
More prone to extinction
Common
1) Rarity
Rare
N
2) Dispersal ability
N
t
t
Poor dispersal
Habitat destroyed
Not able to reach
new fragment
Good dispersal
Habitat destroyed
Habitat fragments
Can reach new
fragment
Habitat fragments
3) Degree of specialization
High specialization
Low specialization
Fig. 3.10a
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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)
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Less prone to extinction
More prone to extinction
4) Population variability
Low variability
High variability
N
5) Trophic status
Population size
relatively constant:
extinction unlikely
Sudden population
decline can lead to
extinction
N
t
t
High trophic status
Pyramid of
numbers
Low trophic status
Top carnivores
Carnivores - tens
Herbivores - hundreds
Plants - thousands
Fig. 3.10b Characteristic that make species particularly vulnerable
to extinction.
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More prone to extinction
6) Life span
Short life span
Less prone to extinction
Long life span
7) Reproductive ability
High reproductive ability
Low reproductive ability
Fig. 3.10c Characteristic that make species particularly vulnerable
to extinction.
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