Extinction and adaptive radiation Flashcards
What are the two views of life since the Cambrian explosion and what do they show?
Cone of increasing diversity
Decimation and diversification
Both show adaptive radiation (increasing diversity)
Both show extinction (loss of diversity)
Diversity is determined by the rate of each process
What is adaptive radiation?
organisms diversify rapidly from an ancestral species into a multitude of new forms which can be observed at a variety of taxonomic scales.
All organisms
Amniotes (the descendants of the last common ancestor of the reptiles)
Primates
What is an examples of adaptive radiation?
Darwin’s Finches, Galapagos
Fruit flies, Hawaii
Lemurs, Madagascar
What situations cause adaptive radiation?
*Colonisation of a new area free of competitors–>Adaptations to exploit new resources–>Beaks in Darwin’s finches
*Adaptive breakthrough–>Adaptations to exploit new resources–>Colonisation of land by plants and animals
*Extinction of competitors–> Adaptations to exploit previously used resources–>Mammals following extinction of dinosaurs
*Replacement of competitors–>(1) Superior adaptation or (2) environmental change–>Overgrowing in Bryozoans
How can we find evidence for extinction?
*Direct observation- Recent extinctions with anthropogenic causes
*Fossil record- Presence of forms no longer living but it is difficult to infer what happened.
What are the scales of extinction?
*Small scale extinction – local and occur over a short period of time. Small scale – loss of species with limited distribution; can accumulate to cause complete extinction
‘Mass extinction’ – global or continental occurs over long stretches of time. Large scale – loss of species and taxa
What can cause small scale extinctions?
*Biotic – parasites, pathogens, competitors – Losing an evolutionary arms race.
*Physical – change in climate (environmental changes happen faster than the rate of adaptation)
*Developmental constraints prevent adaptations to change
What factors affect the chance of extinction?
*Population size – small or isolated populations more likely to become extinct than large connected ones.
*Longevity – short lifespan more susceptible than long lived species.
*Rate of increase – few young and reproduce irregularly more susceptible than species with high reproductive outputs
Stability of environment.
It is inevitable for extinction to occur over geologic time-scales.
What are the ‘Big five’ mass extinctions and give time (mya)?
Late Ordovician 400mya
Late Devonian 350mya
End Permian 250mya
Late Triassic 210mya
End Cretaceous 80mya
The average rate of extinction appears to have declined
There have been recurrent rounds of mass extinction (50-96% extinction)
How can we Interpret mass extinctions?
What was the biggest mass extinction?
Extinction is not a special event – it happens all the time
No single type of event leads to mass extinction
To distinguish between ‘background extinction’ and ‘mass extinction’.
End-Permian =Biggest in history -80-96% of species lost
The K-T mass extinction
What is the best evidence for this?
The best studied example
Separates the Cretaceous -Tertiary boundary
Affected every group of animals and plants
Best evidence given by microfossils – Foraminifera
Dinosaurs and Ammonites went extinct but crocodiles survived
What Caused the K-T mass extinction and how do we know?
Rocks from the K-T boundary had high concentrations of rare metals and extra-terrestrial objects contain similar levels which suggests a large asteroid collided with the Earth.
What is the asteroid impact theory of K-T mass extinction?
Chicxulub, crater 112 miles in diameter in (Yucatán, Mexico)
7.5 – 9 miles in diameter
108 megatons blast
Concurrent impacts as an even larger asteroid broke up?
Global dust cloud blocks sunlight for several years (limiting plants and food)
Global warming
Acid rain
Vulcanisation
Global fires
What are the four pieces of evidence support the asteroid-impact theory?
Iridium anomaly
Chicxulub crater
Rock structures
Simultaneous extinction
Amonites
Bivalves
Brachiopods
Vertebrates (dinosaurs)
What are other causes of mass extinction
Changes in sea level / climate
Changes in shape of continents
High levels of volcanic activity
All are events that catastrophically change the global environment but are not mutually exclusive
