extinctions

99.9% of all species that ever existed are now extinct

Does this statement surprise you?

Why or why not? Do you disagree?

Objectives

• Review the Earth’s extinction history

• Discuss the current mass extinction problem

Biodiversity at Risk

• Life on Earth has a long history of mass extinctions, AND is currently experiencing a mass extinction event.

• Reasons:– Competition– Global/Environmental change– Catastrophe

• Meteor strikes• volcanism

Time

P-T Crisis

K-T Crisis

Pleistocene

Permo-Triassic Extinction

• Within a 5 million year time span..– The Earth lost…

• 52% of families• 60% of genera• And 95% of species

Causes?

• Asteroid impact off of Australia

• Ocean Currents slowing

• Toxic gases

• "Toward the end of the Permian, we had a warming climate with much more carbon dioxide than today, ocean circulation was extremely sluggish, and the oceans became anoxic—essentially deprived of oxygen,"

• Salinity in sea dropped• Atmosphere went from

high oxygen to low during permian

• Warming• Extreme erosion of land • Dead organic matter

flooded the seas; reducing oxygen levels, devastating marine life

• Geomagnetic reversal• Massive volcanism in

present day Siberia

Permo-Triassic Extinction

• Floating species (plankton) and swimming species (nekton) suffered more extinctions than bottom-dwelling species (benthos).

Permo-Triassic Extinction

• insects had severe losses. • A great peak in fungus spores marks the P-Tr

boundary, a sign of massive plant and animal death and decomposition.

• Higher animals and land plants underwent significant extinctions, though not as devastating as in the marine setting.

• Among the four-legged animals (tetrapods), the ancestors of the dinosaurs came through on top.

Permo-Triassic Extinction

• Slow to recover

• Early successional plants

• Fungus spores

• No reefs or coal deposits

• Many marine species disappeared and then reappeared millions of years later– Lazarus species.

Permo-Triassic Extinction

Time

P-T Crisis

K-T Crisis

Pleistocene

Cretaceous-Tertiary Extinction

• Extinction of the non-avian dinosaurs

• Plankton in the seas hit hard.

• Marine life• Vegetation• Lost…

– 14% of families– 38% of genera– 65-75% of

species

• Impact of meteor in Gulf of Mexico

• Volcanism

Cretaceous-Tertiary Extinction

Time

P-T Crisis

K-T Crisis

Pleistocene

Pleistocene

• Modern Ice age

The Current Mass Extinction

“Anthropocene” extinction

• No meteors or volcanism• Human-induced mass extinction• extinction rates today are comparable to

those of the great past extinctions. For example, for birds, of about 10,000 species worldwide, at least 128 have disappeared in the last 500 years, about 1,200 are currently seriously threatened with extinction (all but three from human activities); there is a real prospect of the loss of 500 bird species within this century.

Endangered and threatened species

• What makes a species prone to extinction?

• small population sizes• Limited ranges• Migratory• Specialists• Exploited by humans

Endangered and threatened species

What are the leading causes of extinctions today?

• Habitat destruction

• Invasive species

• Harvesting, Hunting, Poaching

• Pollution

Endemic species

• Species that only occur in very limited areas– High endemism on

• Tropical rainforests• Islands• Reefs