Mass extinctions Flashcards
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)
Chronospecies
single species changing morphologically, genetically, or ecologically over a long time scale- identify them as a separate species
Psuedoextinction
when a species is presumed extinct but has actually just become a different species
Rates of extinction
historically, 0.1/ million/ year
Biotic mechanisms of extinction
competitive exclusion by a closely related species, prey species develops unbeatable defense, new predator, disease
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
abiotic mechanisms of extinction
niche/habitat no longer supports species, climate fluctuations, sea level change, meteorites, volcanism
Mass extinction
extinction of a large number of unrelated species over a short period of geological time- global distribution
similarities of background and mass extinction
can both have multiple causes, both change evolutionary history
difference of background and mass extinction
different outcomes, mass extinctions= whole communities removed, previously minor species become dominant- fundamental changes
- 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
- 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
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
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
- 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
- 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
- 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
Press-pulse hypothesis
first even stresses environment, second even then occurs and causes a greater-than-expected impact
Sixth Mass Extinction
human impact, high rate of extinction- fast
Planned extinction
directed human efforts to drive species to extinction- “pest” species
