Transcript The Extinction Crisis

Chapter 3
Extinction
© 2002 by Prentice Hall, Inc.
Upper Saddle River, NJ 07458
Chapt. 03
Outline
• Rate of extinction
• Causes of extinction
• Risks confronted by
endangered species
• Characteristics of species and
their relationship to extinction
#2
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The Extinction Crisis
• Extinction
– All individuals die without
producing progeny
• Pseudoextinction
– Species disappear over
evolutionary time
#3
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The Extinction Crisis
• Pseudoextinction
– Lineage transformed into separate
lineages
• Fossil Record
– Extinct species to living species –
1,000:1
#4
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Extinction Crisis (cont.)
• Fossil Record (cont.).
– Average life span of a species – 4
million years
– Average extinction rate – 2.5
species per year
#5
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Extinction Crisis
• Fossil Record
– Total number of species over time
– 10 million
• Biased fossil record
– Favors successful, geographically
wide-ranging species
– Persist longer than the average
#6
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Extinction Crisis
• Biased fossil record (cont.)
– 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
#7
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Extinction Crisis
– Background extinction rates are
probably higher than indicated in
fossil record (cont.).
• 1 every 50 years for birds living today
#8
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#9
Extintion Crisis
• Present extinction rate much high than
in the past or predicted.
– Effects due to humans – Distant Past
• Correlation between human population
growth and the number of extinctions
(Figure 3.1)
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#10
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
Chapt. 03
Extinction Crisis
• Effects due to humans (cont.).
– 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
#11
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Extinction Crisis
• Effects due to humans (cont.).
– Large scale extinctions in North and
South America (cont.).
• South America lost 80% of its genera of
large mammals
#12
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Extinction Crisis (cont.)
• Effects due to humans (cont.).
– 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
#13
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Extinction Crisis (cont.)
– Probable causes of these extinctions
• Hunting
• Some climate change
#14
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#15
Extinction Crisis
• 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.
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#16
Extinction Crisis
– Devastating effects on islands
(cont.)
• 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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#17
Extinction Crisis
– Devastating effects on islands
(cont.)
• 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
Chapt. 03
Patterns of Extinction
• Islands vs. continental areas
(Table 3.1)
#18
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#19
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#20
Patterns of Extinction
– Reasons for differences in
extinction rate
• Island species may consist of a
single population
– Single climatic event can lead to
extinction
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#21
Patterns of Extinction
– Reasons for differences in
extinction rate (cont.)
• 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)
100
Habitat loss
Exotic species
Percent endangered
75
Pollution
Hunting
50
Disease
25
0
Continental
U.S. birds
Hawaiian
Birds
Continental
U.S. plants
Hawaiian
plants
Chapt. 03
Patterns of Extinction
• Causes of extinction (Figure
3.3)
#23
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#24
No cause assigned
56%
Introduced animals
17%
Habitat destruction
16%
Hunting
Other causes
10%
1%
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#25
Patterns of Extinction
– 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%).
Chapt. 03
Patterns of Extinction
• Introduced species effects
(cont.)
– Disease and parasitism
• Avain malaria in Hawaii accounted
for the loss of 50% of the local
Hawaiian bird species
#26
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#27
Patterns of Extinction
– Causes of Extinction (Cont.)
• 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
Chapt. 03
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
#28
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Endangered Species
• Factors threatening species
with Extinction (cont.).
– Hunting
– Accidental or deliberate
introduction of exotic species
– Deliberate eradication
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Endangered Species
• Factors threatening species
with Extinction (cont.).
– Incidental
– Disease, both exotic and endemic
#30
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Endangered Species
• Characteristics of Factors
– Human in origin
– Species are threatened with
several factors simultaneously
– Relative importance as measured
by frequency of occurrence
#31
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Endangered Species
• Characteristics of Factors (cont.)
– 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
#32
Threat and classes of threats
Habitat loss & modification: 76%
Cultivation & settlement
Pastoral development
Logging & plantations
Exploitation: 50%
Other
Meat
Fur and hides
Live trade
Introductions: 18%
Others
Predators
Competitors
Limited distribution
Persecution
Disturbance
Incidental take
Disease
Percent of species affected
0
10
20
30
40
50
60
Chapt. 03
Endangered Species
• Significance of hunting –
Valuable fur and wood (Figure
3.6)
• Overexploitation
– Overharvesting for commercial
interests
#34
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Endangered Species
• Overexploitation (cont.). 1998,
– Rare plants are threatened by
collectors
• David Wilcove categorized
threats to plants and animals
in the US
– Five categories
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Endangered Species
– Five categories (cont.)
• Habitat destruction
• Alien species
• Overharvesting
• Disease (both native and alien)
• Pollution
#36
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Endangered Species
– Sample size: 1880 species
– Results (Figure 3.7)
#37
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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Endangered Species
• Categorization of threats by
class of species (Figure 3.8)
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#40
Percentage endangered
0
Mammals
Fish
Birds
Reptiles
Amphibians
All invertebrates
0.5
1
1.5
2
2.5
3
3.5
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Endangered Species
• Categorization of threats by
geographic areas (Table 3.2)
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#42
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Endangered Species
– 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.
#43
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#44
Endangered Species (cont.)
– Bigger countries have more
endangered species than smaller
countries (Figure 3.9)
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#45
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
Country area (1000 ha)
500,000 1,000,000 2,000,000
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#46
Endangered Species (cont.)
– US and endangered reptiles,
amphibians, and fishes
• Better monitoring and documenting
activities
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Endangered Species
• Correlations between human
factors and extinction
– 1995, Kerr and Currie Compared
90 countries
– Six indices of human activities
(Table 3.3)
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Endangered Species (cont.)
• Correlation between human
factors and extinction (cont.)
• Human population explained the
most variation in the proportion of
endangered species of birds.
• Per capita GNP explained the most
variation in mammals
#49
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Species Characteristics and
Extinction
• Rarity (Fig. 3.10)
– Determined by
• Geographic range,
• Breadth of habitat
• Local population size
• Ability to disperse (Fig. 3.10)
#50
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Species Characteristics and
Extinction (cont.)
– Rescuing a population through
immigration
• Degree of specialization (Fig.
3.10)
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Species Characteristics and
Extinction (cont.)
• Degree of specialization (cont.)
– Organisms that are specialized
are more likely to become extinct
• Limited food
• Limited habitat
#52
Less prone to extinction
More prone to extinction
Common
1) Rarity
Rare
N
2) Dispersal ability
N
t
Poor dispersal
Habitat destroyed
Not able to reach
new fragment
Habitat fragments
3) Degree of specializationHigh specialization
t
Good dispersal
Habitat destroyed
Can reach new
fragment
Habitat fragments
Low specialization
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Species Characteristics and
Extinction (cont.)
• 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
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#55
More prone to extinction
Less 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 are very few, so prone to extinction as
Carnivores - tens
Herbivores - hundreds
Plants - thousands
Chapt. 03
Species Characteristics
and extinction (cont.)
• Life span (Fig. 3.10)
• Reproductive ability (Fig. 3.10)
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#57
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
Chapt. 03
Summary
• Important causes of extinction
– Introduced species (39%)
– Habitat destruction (36%)
– Direct exploitation (23%)
#58
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Summary (cont.)
• Factors threatening species
– Habitat destruction
• Deforestation and ecosystem
conversion
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Summary (cont.)
• Species characteristics affecting
the sensitivity to extinction
–
–
–
–
Rarity
Ability to Disperse
Degree of Specialization
Population variability
#60
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Summary
• Species characteristics affecting
the sensitivity to extinction (cont.)
– Trophic Status
– Longevity
– Reproductive ability
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Discussion Question #1
• Which type of organisms do
you think deserve priority in
conservation efforts and why?
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Discussion Question #2
• What ecological information
would you need in order to list
a species as endangered?
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Discussion Question #3
• If we are concerned with
protecting rare species, should
we also be concerned with
protecting subspecies (or
races) or even individual
populations? Discuss the pros
and cons of this issue.
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