EXTINCTION

Evidence from the past

• The fossil record remains first and foremost among the databases that document changes in past life on Earth.

• The fossil record clearly shows changes in life through almost any sequence of sedimentary rock layers.

• Successive rock layers contain different groups or assemblages of fossil species.

3 Types of Extinction

1. Local extinction (extirpation) species no longer found in an area where it was once found

• Still found elsewhere (= population extinction)

2. Ecological extinction so few members of a species are left that it can no longer play its ecological role in the ecosystem

3. Biological extinction species is no longer found anywhere on the earth

Mass Extinctions Epoch Cause Species Lost

Precambrian Glaciation Stromatolites

Cambrian O2 Depletion Olnellids

Ordovician Glaciation of Gondwana

Brachiopods

Devonian Meteor, Glaciation Early corals

Permian Pangea Trilobites

End Cretaceous Meteor, Volcanoes Dinosaurs

Holocene Humans All forms

Permian mass Extinction

- Permian Period (286-248 million years ago) Formation Of Pangea

- Terrestrial faunal diversification occurred in the Permian

- 90-95% of marine species became extinct in the Permian (largest extinction in history)

- Causes? = Formation of Pangea reduced continental shelf area, glaciation, Volcanic eruptions

The End-Cretaceous (K-T) Extinction

- Numerous evolutionary radiations occurred during the Cretaceous (144-65 million years ago) 1st appearance of dinosaurs, mammals, birds, angiosperms

- A major extinction occurred at the end of the period- 85% of all species died in the End-Cretaceous (K-T) extinction (2nd largest in history)

- Causes? = Meteor impact in the Yucatan, Volcanic eruption both supported geolocially, cause climate change, atmospheric changes

Extinction Rates• Biologists estimate that 99.9% of all species ever in

existence are now extinct– Background extinction – local environmental changes

cause species to disappear at low rate– mass extinction – catastrophic, widespread (25 – 75%

of existing species– mass depletion – higher than background but not mass

• Cause temporary biodiversity reductions but create vacant niches for new species to evolve

• 5 million years of adaptive radiation to rebuild diversity after extinction

Premature extinction from human causes

Passenger pigeon

Great auk Dodo Dusky seaside sparrow

Aepyornis(Madagascar)

Main factors Overhunting, Habitat Destruction &Introduction of Exotic Species

Differences in Cause of Extinction

Historically most mass extinctions were caused by

• Catastrophic Agents- such as meteorite impacts and comet showers,

• Earth Agents- such as volcanism, glaciation, variations in sea level, global climatic changes, and changes in ocean levels of oxygen or salinity

Currently a mass extinction is being caused by the actions of 1 species Us

Which species are most vulnerable?

• Vulnerability of species affected by …– Numbers – low numbers = automatic risk– Degree of specialization = generalists adapt better

than specialists– Distribution = widely distributed organisms, may

migrate out of harms way & different effects by area– Reproductive potential – if low = vulnerable– Reproductive behaviors – how complex, picky, …– Trophic level – higher are more vulnerable to

biomagnification & trophic cascades

Characteristic Examples

Low reproductive rate(K-strategist)

Specialized niche

Narrow distribution

Feeds at high trophic level

Fixed migratory patterns

Rare

Commercially valuable

Large territories

Blue whale, giant panda,rhinoceros

Blue whale, giant panda,Everglades kite

Many island species,elephant seal, desert pupfish

Bengal tiger, bald eagle,grizzly bear

Blue whale, whooping crane,sea turtles

Many island species,African violet, some orchids

Snow leopard, tiger, elephant, rhinoceros, rare plants and birds

California condor, grizzly bear, Florida panther

Indian Tiger

Range 100 years ago

Range today(about 2,300 left)

Black Rhino

Range in 1700

Range today(about 2,400 left)

African Elephant

Probable range 1600

Range today(300,000 left)

Asian or Indian Elephant

Former range

Range today(34,000–54,000 left)

Vulnerability of ecosystems

1. Diversity at species, genetic, ecological or functional levels

** Remember, Diversity = Stability **

2. Resilience Ability of a living system to restore itself to original condition after being exposed to a minor outside disturbance

3. Inertia ability of a living system to resist being disturbed or altered

Biome % of Area Disturbed

Temperate broadleaf forests

Temperate evergreen forests

Temperate grasslands

Mixed mountain systems

Tropical dry forests

Subtropical and temperate rain forests

Cold deserts and semideserts

Mixed island systems

Warm deserts and semideserts

Tropical humid forests

Tropical grasslands

Temperate boreal forests

Tundra

94%

94%

72%

71%

70%

67%

55%

53%

44%

37%

26%

18%

0.7%

Leading causes of wildlife depletion & extinction

1. Habitat loss, fragmentation or degradation

• Agriculture, urban development, pollution• Prevent dispersal, mating, gene flow

2. Deliberate or accidental introduction of non-native species

• Rapid reproduction, no competitors, no predators, upset energy flow

Overfishing

Habitatloss

Habitatdegradation

Introducingnonnativespecies

Commercialhunting

andpoaching

Sale ofexotic pets

anddecorative

plants

Predatorand

pest control

Pollution

Climatechange

Basic Causes

• Population growth• Rising resource use• No environmental

accounting• Poverty

Case Studies - Elephants

Endangered 1. Ecological pressures – shrinking habitat2. Socio-political pressures – recovery of

elephants in smaller habitats = widespread habitat destruction, other species now poached for ivory

3. Economic pressures – poaching for ivory

• Ecological Role – keystone species, maintains grassland community by removing trees

• Consequences – loss of ecosystem type

Case Studies – Passenger Pigeon

Extinct September 1, 1914 1. Ecological pressures – clearing virgin forests for

agriculture lost food & nests, 1 egg laid per year2. Socio-political pressures – Supply meat for

growing east coast cities3. Economic pressures – easy capture in large

dense flocks, roosts markets in the east

• Ecological Role – once most numerous bird on the planet

• Consequences – linked to spread of lyme disease

Case Studies – American Alligator

Recovered June 4 19871. Ecological pressures – shrinking habitat2. Socio-political pressures – alligator nuisance,

sustainable use, tourism3. Economic pressures – confused with American

Crocadile hunted for skins

• Ecological Role – keystone predator, gator holes in everglades, top carnivore

• Consequences – loss of fish & bird populations & change whole everglades ecosystem structure / now healthy systems

Alligator mississippiensis

Remember

• That current changes in species numbers will be exacerbated by global warming

When is endangered really “in danger”

• Is there a number where the population is too small to survive?

• MVP = minimum viable population the smallest number of individuals necessary to ensure the survival of a population in a region for a specified timer period

• Time range typically 10-100 years• Most indications are that a few thousand

individuals is the MVP if time span is > 10 years

Genetic Bottlenecks

• If populations recover from times with small numbers other problems can persist

• Genetic bottlenecks• Think of a traffic bottleneck many cars

approach and stop, only a few get through.• Same with genes – genetic diversity is

dramatically reduced• When populations are reduced to small

numbers interbreeding occurs and genetic diversity plummets

Cheetahs• A few thousand years ago cheetahs

experienced a population crash• They have since recovered but they are

almost all genetically identical• Why is this a problem?

1. Inbreeding increased the chances of deformity from recessively inherited diseases

2. Identical genes gives identical vulnerability to disease

3. Weakened physiology – exaggerated recovery time from activity makes them vulnerable

References

• www.rainforestweb.org

• www.redlist.org