Extinctions and how to change diversity

1. Sepkoski’s Curves and others.

2. How to change diversity

3. Models of diversity increase

4. Perturbations to the curves

5. End Permian event

6. End Cretaceous event

1a. Sepkoski’s Curves and others

Family diversity

Time

200

100

Time

Orders

Different taxonomic levels affect the shape of the curves

500

1000

Marine invertebrates

EndPermian

EndOrdovician

400

600

200

Species

Vascular land plants

Families

EndOrdovician

EndPermian

300

100

Families

EndOrdovician

EndPermian

Terrestrial tetrapods

600

200

Families

EndPermian

EndOrdovician

Insects

1b. Sepkoski’s Curves and others

2. How to change diversity

Diversity = origination - extinction

Diversity

Time

Diversity increases bya. Higher origination ratesb. Lower extinction rates

Diversity decreases bya. Lower origination ratesb. Higher extinction rates

Origination - Darwinian evolution. Changes of shape with time.Extinction - consequence of competition, selective or general

3. Models of diversity increase

Time

Diversity Logistic - ecosystems ‘fill’

Additive

Exponential - ecosystems don’t ‘fill’

Additive model implausible. Implies slower ratesof evolution with time. Others both have merit.Logistic curve is a good fit for marine invertebratesExponential curve is a good fit for non-marine tetrapods.Both may be correct in some circumstances. Or just hard to tell apart in early stages (a scale effect)

4. Perturbations to the curves

Time

Diversity Mass extinctions

Mass extinctionsperturb system.Reset curves.

Mass extinctions reset diversity curves.They are major events in the history of life.Fast recovery from these events may suggest agenerally logistic model of diversification.

5. End Permian event

60% families extinct95% species extinctMarked end of Palaeozoic faunaTrilobites, rugose, tabulate coralsextinct.Difficult to attribute causeMay be related to odd tectonic configuration

Pangaea

Mid

Per

mi a

n L

a te

Pe r

mia

n E

arl y

Tr i

assi

c

Sealevelrise

Sibe

rian

trap

eru

ptio

ns

Shal

low

mar

ine

anox

ia

Dee

p m

arin

e an

oxia

Fungal

spike

Marinebenthos

Reefs

Terrestrial tetrapods ?Two extinctions

30% families extinct65% species extinctDinosaurs, marine and flying reptiles,ammonites extinct.Two likely causes -a. Meteorite impactb. Deccan Trap volcanism

6. End Cretaceous event

Core

Crust

D’’ layer

Mantleplumes

Cretaceous Palaeogene

Iridiumspike

Shockedquartz

Micro-tektites

Yucatanimpactcrater Deccan

traps