3: Extinction Flashcards
List the types of extinction
Contemporary:
Local
Species
Geological:
Background
Extinction events
Mass extinction events
Describe the global extinction crisis
→ 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
Define local extinction
loss of a pop. from a particular area e.g wolves from Britain
Give an example of species extinction
passenger pigeon (used to be the most abundant species in NA), hunted to extinction
Define background extinction
the sum of all normal species terminations during a defined time interval
Define extinction events
times when many species go extinct for a shared reason, typically regional rather than global but selective to clades
Define mass extinction events
times of geographically rapid global disappearance of life, many species of a wide ecological range die out worldwide
List the 5 big mass extinction events
- Late Ordovician
- Late Devonian
- Late Permian
- Late Triassic
- Late Cretaceous
Describe the End-Ordovician mass extinction
444 mya
Declines : nautiloids, trilobites, brachiopods, crinoids, bryozoans, corals
Cause: glaciation
Describe the Late Devonian mass extinction
372 mya
Declines: Trilobites, brachiopods, bivalves, corals, nautiloids, sponges, crinoids, fishes
Complete loss: ostracoderms, placoderms
Causes: Large Igneous Province (LIP) and resulting ocean anoxia
Describe the End-Permian mass extinction
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
What does LIP stand for what what is it?
Large Igneous Province
= large accumulation of igneous rocks (formed when magma is trapped and solidifies) mostly made from iron/magnesium
Describe the End-Triassic mass extinction
201 mya
Declines: Bivalves, ammonoids, gastropods
Complete loss: conodonts, basal archosaurs
Causes: LIP, ocean anoxia
Describe the end-cretaceous mass extinction
66 mya
Declines: bivalves, foraminifera
Complete loss: Dinosaurs, pterosaurs, plesiosaurs, mosasaurs, ammonites, belemnites
Causes: meteorite impact, LIP
Describe the survivors of a mass extinction event and why they are important
- 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
Describe species senescence theory
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)
What is the red queen hypothesis of competition?
Competition can drive evolution towards maladaptive phenotypes = extinction
Competition drives speciation
Describe the court jester hypothesis.
Random perturbations to the environ rather than biotic interactions are initiators of major changes in organisms and ecosystems
Climate drives extinction
What is species selection?
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
What are the requirements of species selection?
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
What is broad sense species selection?
aggregate traits (body size), averaging values
What is strict sense species selection?
Emergent traits (e.g range size), can only be measured at the whole species level
