3: Extinction

Question 1

List the types of extinction

Answer 1

Contemporary:
Local
Species

Geological:
Background
Extinction events
Mass extinction events

Question 2

Describe the global extinction crisis

Answer 2

→ 1 million species threatened with extinction
→ across a wide range of taxonomic groups, on average about 25% of species are threatened with extinction when assessed using IUCN Red List criteria

Question 3

Define local extinction

Answer 3

loss of a pop. from a particular area e.g wolves from Britain

Question 4

Give an example of species extinction

Answer 4

passenger pigeon (used to be the most abundant species in NA), hunted to extinction

Question 5

Define background extinction

Answer 5

the sum of all normal species terminations during a defined time interval

Question 6

Define extinction events

Answer 6

times when many species go extinct for a shared reason, typically regional rather than global but selective to clades

Question 7

Define mass extinction events

Answer 7

times of geographically rapid global disappearance of life, many species of a wide ecological range die out worldwide

Question 8

List the 5 big mass extinction events

Answer 8

• Late Ordovician
• Late Devonian
• Late Permian
• Late Triassic
• Late Cretaceous

Question 9

Describe the End-Ordovician mass extinction

Answer 9

444 mya
Declines : nautiloids, trilobites, brachiopods, crinoids, bryozoans, corals
Cause: glaciation

Question 10

Describe the Late Devonian mass extinction

Answer 10

372 mya
Declines: Trilobites, brachiopods, bivalves, corals, nautiloids, sponges, crinoids, fishes
Complete loss: ostracoderms, placoderms
Causes: Large Igneous Province (LIP) and resulting ocean anoxia

Question 11

Describe the End-Permian mass extinction

Answer 11

252 mya
→ biggest of all mass extinction events, estimated 95% of life was lost
Declines: Brachiopods, crinoids, synapsids
Complete loss, blastoids, trilobites, rugose & tabulate corals, pareiasaurs
Causes: LIP, ocean anoxia

Question 12

What does LIP stand for what what is it?

Answer 12

Large Igneous Province
= large accumulation of igneous rocks (formed when magma is trapped and solidifies) mostly made from iron/magnesium

Question 13

Describe the End-Triassic mass extinction

Answer 13

201 mya
Declines: Bivalves, ammonoids, gastropods
Complete loss: conodonts, basal archosaurs
Causes: LIP, ocean anoxia

Question 14

Describe the end-cretaceous mass extinction

Answer 14

66 mya
Declines: bivalves, foraminifera
Complete loss: Dinosaurs, pterosaurs, plesiosaurs, mosasaurs, ammonites, belemnites
Causes: meteorite impact, LIP

Question 15

Describe the survivors of a mass extinction event and why they are important

Answer 15

• not random, often share ‘generalist’ characteristics
• Significant for modern conservation concerns
  = Characteristics of mass extinction survivors may indicate trajectories of recovery if current extinction crisis proceeds unchecked

Question 16

Describe species senescence theory

Answer 16

Suggests species undergo a lifecycle like individuals (birth, development, reproduction, death)
Orthogenesis → change in organisms was due not to natural selection but to unchecked directional trend within a lineage
e.g the Irish elk (big large antlers)

= disproven (no mechanism, at odds with natural selection)

Question 17

What is the red queen hypothesis of competition?

Answer 17

Competition can drive evolution towards maladaptive phenotypes = extinction

Competition drives speciation

Question 18

Describe the court jester hypothesis.

Answer 18

Random perturbations to the environ rather than biotic interactions are initiators of major changes in organisms and ecosystems

Climate drives extinction

Question 19

What is species selection?

Answer 19

the idea that some lineages have characteristics that make them more likely to speciate or less likely to go extinct
E.g species that are large might be less likely to go extinct, but more likely to speciate
Both examples result in a trend towards large size over evolutionary time

Question 20

What are the requirements of species selection?

Answer 20

Variation: species must differ in the focal trait
Heritability: the trait must be inherited
Differential success: the trait must confer different probabilities of speciation, extinction or both

Question 21

What is broad sense species selection?

Answer 21

aggregate traits (body size), averaging values

Question 22

What is strict sense species selection?

Answer 22

Emergent traits (e.g range size), can only be measured at the whole species level