Extinction Ppt

Extinction

2

Extinction

1. Rate of extinction

2. Causes of extinction

3. Risks confronted by endangered species

4. Characteristics of species and their relationship to extinction

3

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

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

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

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

Population growth and animal extinctions. (left) Geometric increase in the human population.(right) increasing numbers of extinctions in birds and mammals.

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

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

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

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

• Causes of extinction

11


Perc

ent

endangere

d

0

25

50

75

100Habitat loss

Exotic species

Pollution

Hunting

Disease

Continental U.S. birds

HawaiianBirds

ContinentalU.S. plants

Hawaiianplants

13

No cause assigned

Introduced animals

Habitat destruction

Hunting

Other causes

56%

17%

16%

10%

1%The causes of extinctions

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

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


(a) Steller’s sea cow (b) the dodo

(c) the passenger pigeon •(d) the Carolina parakeet

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

1. Habitat loss or modification

2. Hunting

3. Accidental or deliberate introduction of exotic species

4. Disease, both exotic and endemic

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


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

The factors that threaten mammals in Australia and the Americas.

20

Overexploitation

• Significance of hunting – Valuable fur and wood (Figure 3.6)

• Overexploitation

– Overharvesting for commercial interests

– Rare plants are threatened by collectors

21

Five categories

1. Habitat destruction

2. Alien species

3. Over-harvesting

4. Disease (both native and alien)

5. Pollution

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.


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

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.

25

Percentage endangered

0 0.5 1 1.5 2 2.5 3 3.5

Mammals

Fish

Birds

Reptiles

Amphibians

All invertebrates

Percentage of Known species classed as endangered.

26

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


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)

Relationship between number of threatened species and area of a country.

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

30

31

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

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

33

continued…

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)

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


Low variabilityHigh variability

4) Population variability

5) Trophic status

Plants - thousands

Herbivores - hundreds

Carnivores - tens

Top carnivores

Characteristic that make species particularly vulnerable to extinction.

35


6) Life span Short life span Long life span

7) Reproductive ability

High reproductive ability Low reproductive ability

Characteristic that make species particularly vulnerable to extinction.

36

Documents

Extinction Ppt