Chapter 3 Extinction © 2002 by Prentice Hall, Inc. Upper Saddle River, NJ 07458
Chapter 3 Extinction © 2002 by Prentice Hall, Inc. Upper Saddle River, NJ 07458.
Dec 18, 2015
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Chapter 3Extinction
© 2002 by Prentice Hall, Inc.
Upper Saddle River, NJ 07458
#2Chapt. 03
Outline• Rate of extinction• Causes of extinction• Risks confronted by endangered
species• Characteristics of species and
their relationship to extinction
#3Chapt. 03
The Extinction Crisis• Extinction
– All individuals die without producing progeny
• Pseudoextinction– Species disappear over evolutionary
time
#4Chapt. 03
The Extinction Crisis• Pseudoextinction
– Lineage transformed into separate lineages
• Fossil Record– Extinct species to living species –
1,000:1
#5Chapt. 03
Extinction Crisis (cont.)• Fossil Record (cont.).
– Average life span of a species – 4 million years
– Average extinction rate – 2.5 species per year
#6Chapt. 03
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
#7Chapt. 03
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
#8Chapt. 03
Extinction Crisis– Background extinction rates are
probably higher than indicated in fossil record (cont.).•1 every 50 years for birds living today
#9Chapt. 03
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)
#10Chapt. 03
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
#11Chapt. 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
#12Chapt. 03
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
#13Chapt. 03
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
#14Chapt. 03
Extinction Crisis (cont.)– Probable causes of these extinctions
• Hunting• Some climate change
#15Chapt. 03
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.
#16Chapt. 03
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
#17Chapt. 03
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
#18Chapt. 03
Patterns of Extinction• Islands vs. continental areas
(Table 3.1)
#19Chapt. 03
#20Chapt. 03
Patterns of Extinction– Reasons for differences in extinction
rate• Island species may consist of a single
population– Single climatic event can lead to extinction
#21Chapt. 03
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)
Perc
ent
endangere
d
0
25
50
75
100Habitat loss
Exotic species
Pollution
Hunting
Disease
Continental U.S. birds
HawaiianBirds
ContinentalU.S. plants
Hawaiianplants
#23Chapt. 03
Patterns of Extinction• Causes of extinction (Figure 3.3)
#24Chapt. 03
No cause assigned
Introduced animals
Habitat destruction
Hunting
Other causes
56%
17%
16%
10%
1%
#25Chapt. 03
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%).
#26Chapt. 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
#27Chapt. 03
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
#28Chapt. 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
#29Chapt. 03
Endangered Species• Factors threatening species with
Extinction (cont.).– Hunting– Accidental or deliberate introduction
of exotic species– Deliberate eradication
#30Chapt. 03
Endangered Species• Factors threatening species with
Extinction (cont.).– Incidental – Disease, both exotic and endemic
#31Chapt. 03
Endangered Species• Characteristics of Factors
– Human in origin– Species are threatened with several
factors simultaneously– Relative importance as measured by
frequency of occurrence
#32Chapt. 03
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
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
#34Chapt. 03
Endangered Species• Significance of hunting – Valuable
fur and wood (Figure 3.6)• Overexploitation
– Overharvesting for commercial interests
#35Chapt. 03
Endangered Species• Overexploitation (cont.). 1998,
– Rare plants are threatened by collectors
• David Wilcove categorized threats to plants and animals in the US– Five categories
#36Chapt. 03
Endangered Species– Five categories (cont.)
•Habitat destruction•Alien species•Overharvesting•Disease (both native and alien)•Pollution
#37Chapt. 03
Endangered Species– Sample size: 1880 species– Results (Figure 3.7)
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
#39Chapt. 03
Endangered Species• Categorization of threats by class
of species (Figure 3.8)
#40Chapt. 03
Percentage endangered
0 0.5 1 1.5 2 2.5 3 3.5
Mammals
Fish
Birds
Reptiles
Amphibians
All invertebrates
#41Chapt. 03
Endangered Species• Categorization of threats by
geographic areas (Table 3.2)
#42Chapt. 03
#43Chapt. 03
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.
#44Chapt. 03
Endangered Species (cont.)– Bigger countries have more
endangered species than smaller countries (Figure 3.9)
#45Chapt. 03
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)
#46Chapt. 03
Endangered Species (cont.)– US and endangered reptiles,
amphibians, and fishes•Better monitoring and documenting
activities
#47Chapt. 03
Endangered Species• Correlations between human
factors and extinction– 1995, Kerr and Currie Compared 90
countries– Six indices of human activities (Table
3.3)
#48Chapt. 03
#49Chapt. 03
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
#50Chapt. 03
Species Characteristics and Extinction
• Rarity (Fig. 3.10)– Determined by
•Geographic range,•Breadth of habitat•Local population size
• Ability to disperse (Fig. 3.10)
#51Chapt. 03
Species Characteristics and Extinction (cont.)
– Rescuing a population through immigration
• Degree of specialization (Fig. 3.10)
#52Chapt. 03
Species Characteristics and Extinction (cont.)
• Degree of specialization (cont.)– Organisms that are specialized are
more likely to become extinct•Limited food•Limited habitat
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
#54Chapt. 03
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
#55Chapt. 03
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 are very few, so prone to extinction as in 1
#56Chapt. 03
Species Characteristics and extinction (cont.)
• Life span (Fig. 3.10)• Reproductive ability (Fig. 3.10)
#57Chapt. 03
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
#58Chapt. 03
Summary• Important causes of extinction
– Introduced species (39%)– Habitat destruction (36%)– Direct exploitation (23%)
#59Chapt. 03
Summary (cont.)
• Factors threatening species– Habitat destruction
• Deforestation and ecosystem conversion
#60Chapt. 03
Summary (cont.)
• Species characteristics affecting the sensitivity to extinction– Rarity– Ability to Disperse– Degree of Specialization– Population variability
#61Chapt. 03
Summary
• Species characteristics affecting the sensitivity to extinction (cont.)– Trophic Status– Longevity– Reproductive ability
#62Chapt. 03
Discussion Question #1• Which type of organisms do you
think deserve priority in conservation efforts and why?
#63Chapt. 03
Discussion Question #2• What ecological information would
you need in order to list a species as endangered?
#64Chapt. 03
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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