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ENVR 202 pt. 2 > Mass extinctions > Flashcards

Flashcards in Mass extinctions Deck (20):
1

Background rate of extinction

average number of FAMILIES (easier to tell apart) going extinct, figure it out by examining the fossil record (limits in the fossil record)

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Chronospecies

single species changing morphologically, genetically, or ecologically over a long time scale- identify them as a separate species

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Psuedoextinction

when a species is presumed extinct but has actually just become a different species

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Rates of extinction

historically, 0.1/ million/ year

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Biotic mechanisms of extinction

competitive exclusion by a closely related species, prey species develops unbeatable defense, new predator, disease

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evolutionary causes for extinction vulnerability

poor disperser, at or near the top of the food chain, small range, rare, low genetic variability, specialized requirements, large body size

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abiotic mechanisms of extinction

niche/habitat no longer supports species, climate fluctuations, sea level change, meteorites, volcanism

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Mass extinction

extinction of a large number of unrelated species over a short period of geological time- global distribution

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similarities of background and mass extinction

can both have multiple causes, both change evolutionary history

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difference of background and mass extinction

different outcomes, mass extinctions= whole communities removed, previously minor species become dominant- fundamental changes

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1. End Ordovician mass extinction

49% animal genera lost- marine organisms suffered most, caused by: volcanic activity depositing silicate materials- CO2 in air deposited in sea, less CO2 in atmosphere and less greenhouse effect- colder, & land moves to the south pole- glacier formation- less water in oceans

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2. Late Devonian

20% of families, 70-80% of animal species lost, shallow water species impacted- dominant reef builders lost, unusually long, no single cause, combination of silicate weathering cooling globe and phosphorus erosion

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Devonian plant hypothesis

large number of plants led to global cooling and lack of oxygen in oceans, CO2 in atmosphere combines with water to form carbonic acid- falls as acid rain and weathers silicates- bicarbonate erodes and ends up in ocean- CO2 in atmosphere sequestered as limestone in ocean- sped up by plants- break apart rocks and also secrete own acids

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Formation of dead zones

chemical weathering of rocks by plants releases phosphorus- erodes to ocean, leads to algal blooms- algae dies and drifts down- bacteria uses oxygen to break down algae- low oxygen levels in that area

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3. End Permian

"the great dying"- 70% terrestrial vertebrates 96% marine species lost- all life today descendants of the few survivors here; causes- series of massive volcanic eruptions- release CO2, methane, SO2 and burned coal deposits- global warming; lost half of oxygen content; ocean salinity increased- deep water circulation more difficult; buildup of dead matter and dead zones

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4. End Triassic

76% species extinct- left empty niches on land led to rapid diversification of dinosaurs; no clear cause: gradual climate change; more minor asteroid impact; massive volcanic eruption

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5. End Cretaceous

75% plant and animals species extinct- only smaller tetrapods survived, end of dinosaurs, followed by rise of mammals - rapid adaptive radiation; causes: impact hypothesis massive bolide impact, threw cloud of particles into atmosphere- global winter- interfered with photosynthesis by blocking sunlight; proof of impact in crater and iridium sediment buildup in rock layers; Deccan Traps (india)- massive basalt floods produced similar effect as previously with volcanic activity; both contributed

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Press-pulse hypothesis

first even stresses environment, second even then occurs and causes a greater-than-expected impact

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Sixth Mass Extinction

human impact, high rate of extinction- fast

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Planned extinction

directed human efforts to drive species to extinction- "pest" species