15 Extinction Flashcards
What are the types of extinction?
Contemporary:
- Local extinction
- Species extinction
Geological:
- Background extinction
- Extinction events
- Mass extinction events
What is local extinction?
Loss of a population from a particular area
e.g. wolves from Britain
What is species extinction?
Complete loss of a species
e.g. from pressures of hunting
What types of extinction are in the fossil record?
Background extinction
Extinction events
Mass extinction events
What is background extinction?
The sum of all normal species terminations during a defined time interval
What are extinction events?
Times when many species go extinct for a shared reason, typically regional not global in scale
- Pertaining to selective extinction of clades
What are mass extinction events?
Times of geologically rapid global disappearance of much of life, when many species of wide ecological range died out worldwide
How has extinction rate changed over time?
Apparent decline - due to statistical anomaly
No general trend after accounting for statistical artefacts
Mass extinctions identified as data points outside the 99% confidence interval of the line of best fit
What are the major mass extinctions?
End-Ordovician 440mya
End-Devonian 360mya
End-Permian 250mya
End-Triassic 200mya
End-Cretaceous 65mya
What happened in the End-Ordovician extinction?
440mya
Caused by worldwide glaciation
Declines in marine nautiloids, trilobites, brachiopods, crinoids, bryozoans, corals
What happened in the End-Devonian extinction?
360mya
Caused by LIPs, ocean anoxia
Declines in trilobites, brachiopods, bivalves, corals, nautiloids, sponges, crinoids, fishes
Complete loss of ostracoderms and placoderms
What happened in the End-Permian extinction?
250mya
Caused by LIPs, ocean anoxia
Declines in brachiopods, crinoids, synapsids
Complete loss of blastoids, trilobites, rugose & tabulate corals, pareiasaurs
What happened in the End-Triassic extinction?
200mya
Caused by LIPs, ocean anoxia
Declines in bivalves, ammonoids, gastropods
Complete loss of conodonts, basal archosaurs
What happened in the End-Cretaceous extinction?
65mya
Caused by meteorite impact, LIPs
Declines in bivalves, gastropods, foraminifera
Complete loss of dinosaurs, pterosaurs, plesiosaurs, mosasaurs, ammonites, belemnites
What are “disaster taxa”?
Species that do well in the face of a natural geographic disaster
Survivors of mass extinctions are not random
Often share “generalist” characteristics
Why are mass extinction survivors significant for modern conservation concerns?
If certain species removed, scaffold of the ecosystem may be available after the crisis for the new species to occupy
But if most ecosystem components are removed by a larger event, recovery may involve construction of new ecosystems
What might characters of mass extinction survivors indicate?
Trajectories of recovery if the current extinction crisis proceeds unchecked
What is species senescence?
Suggestion that species undergo a lifecycle like individuals
- Birth
- Development
- Reproduction
- Death
What is orthogenesis?
Change in organisms was not due to natural selection, but to unchecked directional trends within a lineage
- There is no mechanism for this
- Completely at odds with natural selection
- Evidence falls away on closer examination
Why do only some species go extinct?
Biotic factors - competition and the Red Queen (running to stay in place)
Abiotic factors - Court Jester
- Random perturbations to the physical environment e.g. climate change, tectonic events change the ground rules for biota
- Hypothesis - changes in physical environment rather than biotic interactions themselves are initiators of changes in organisms and ecosystems
What factors explain the probability of speciation and extinction?
Diversity (competition), biotic factors, drives speciation
Climate, environmental factors, 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 or just or likely to go extinct but more likely to speciate
Both of these 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 - trait must be inherited
Differential success - trait must confer different probabilities of speciation, extinction, or both
What is broad sense species selection?
Aggregate traits e.g. body size
What is strict sense species selection?
Emergent traits e.g. range size
