Reading Assignments

• BSCI – Chapter 7

• CONS – Chapters 4-5

Deterministic vs. Extrinsic Stochastic Threats

Fre

quen

cy

Mean

Growth Rate

Stochastic Threats and Population Size

time

ln(N)

time

ln(N)

“Quiz”

time

ln(N)

The aspen sunflower

Environmental Variation

1974 1977 1980 1983 1986 1989 1992 1995 1998 2001

Nu

mb

er

of

flo

we

r h

ea

ds

0

500

1000

1500

2000

2500

3000

3500

4000

Good years . . .

Bad years

Snowpack and Frost Damage

How might climate change affect this sunflower?

Species / Population B

Species / Population A Extinction by geneticswamping

Hybridization

Species B’

Causes of Extinction(Genetic Swamping)

Time

What IS Causing Extinction?

Habitat Destruction 73

Introduced species 68

Chemical pollutants 38

Hybridization 38

Overharvesting 15

Extinction Threats for North American Freshwater Fishes (IUCN)

Topics: Historical Extinctions

• What is the background rate of extinctions?

• What are mass extinctions?

• How long does recovery from mass extinctions take?

• Causes of select prehistoric extinctions.

• What is the current rate of extinctions?

“Pseudo-extinction”

Cladogenesis Anagenesis

Sideling Hill, MD

Stratigraphic Geology(study of layered rock)

• Sedimentation

• Stratum (singular)

• Beds = strata > 1 cm

• Lamina(e) = stratum(a) < 1 cm

• Lithification

• Fossils

Characteristics of a ME

• Brief relative to the expected duration of the taxa

• Involve considerable numbers of taxa

Proposed Agents of Mass Extinctions

• Changes in climate and sea level (marine regression).

• Asteroid impacts (especially K/T).

Stanley’s research on bivalves during Pleistocene

cold adapted: no changewarm adapted: no change

Gulfstream

cold adapted: no changewarm adapted: declined

Glacier

Climate Change

Marine Regression

Continentalshelf: lossof habitat

refuges

Current sea level

Conicalisland: no

loss of habitat

Marine Regression

• 87% of recent marine families have > 1 species in shallows.

• Expected extinction with refuges: 100 - 87 = 13%.

• Observed extinction of families: 52% (Permian).

• Conclusion: marine regression is not the only cause of mass extinction (Jablonski).

Climate Change Evidence

• There were major glaciations at the beginning of the Ordovician and Devonian ME’s.

• No major glaciations accompanied the Permian, Triassic and Cretaceous ME’s.

• Another major glaciation, ca. 300 million years ago, and lasting 90 million yrs, did not result in an ME.

• Tentative Conclusion: glaciations might cause extinctions in marine invertebrates, but are not currently regarded as a necessary cause for ME’s.