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Week 11: EXTINCTION
Speciation adds new species(+) OVERALL DIVERSITY(-)Extinction
removes species
Extinction is a normal evolutionary process occurring
continuously throughout geological time
Background extinction rate:
mean rate of extinction of animal families in geological time
3-4 per million years loss of 1-2 sp. every 1 to 10 yrs* Average
sp. duration in fossil record 1-20 million years
Accidents causes extinction
Small populations (e.g. species with small geographic ranges)
are prone to accidents
Species with small ranges have a high probability of extinction,
since they
have fragmented (disjunct) ranges occupy fewer sites with the
range have smaller population sizes are likely at the limits of
their environmental toleranceEX: bivalves and gastropods in late
Cretaceous extinctions spp. with large ranges showed a
significantly higher chance of survival
Distribution and abundance:rare common
widespread or cosmopolitan --- Likely to survive
narrow or 'endemic' Likely to become extinct ---
* Cosmopolitan vs. endemic spp. (relative terms)
What accidents lead to extinction?
EX: population fluctuations, volcanic eruptions, 'normal'
climatic fluctuations, natural
disasters, competition with immigrants, evolution of new
predators or competitors, etc.
Mass Extinctions
Def: >50% global loss of spp. (>75% in Barnosky et al.
paper), very sudden, broad taxonomic
coverage, results in changes to surviving biotaPotential causes
of mass extinction include dramatic changes in: ocean circulation,
global climatic,
sea level potentially associated with dramatic events (e.g.
volcanic eruptions, asteroid
impacts)
Big Five Mass Extinctions:
1. Ordovician (438 myr)
26% marine families; 85% spp.
Theory: climate change (glaciation), sea-level regression,
anoxia
2. Devonian (375 myr)
22% families; 80% spp.
Theory: global temperature decline, sea-level decline, meteorite
impact3. Permo-Triassic, The mother of all mass extinctions (248
myr)
52% families; 96% spp.
Recorded in the Siberian Traps (flood basalts)
Theories: SYNERY of... productivity decline, continental shelf
area decline,
cosmic radiation, provinciality decline, asteroid impact,
global
warming/cooling, volcanism, anoxia
4. Late Triassic (206 myr)
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Theory: increased aridity, sea-level regression, impact,
rifting
5. Cretaceous-Tertiary (65 myr)
16% families; 75% spp. (bye-bye dinos!)
Alvarez et al. (1980) observe spike in iridium (rare on Earth,
common in
meteorites) eventually they track down the crater from an
asteroid 10
km in diameter, capable of causing extinction on a mass
scale
Theory: asteroid impact volcanic eruption global climate changeA
more recent extinction: Pleistocene Extinction
Affected mostly terrestrial biota (mostly mammals, fewer
birds)
Dramatic changes in geographic ranges of plants, animals, and
marine organisms
Body size changes in surviving spp. (megafauna hit hard)
Global temp trends: Cooling in Pliocene-Pleistocene, recent Late
Pleistocene warming
An estimated 1680 mammal spp. extinct (relative to 4327 known
extant mammal spp.)
Humans implicated as catalysts
Are we in the 6th mass extinction?
PAPERS!!
BARNOSKY ET AL. 2011 Has the Earths sixth mass extinction
already arrived?
-they argue technically not, because the qualifying number of
species (75%) has not been lost
-BUT if threatened/endangered species are lost, we could
potentially reach mass extinction
levels in as little as three centuries
LAVOUE ET AL. 2010 Remarkable evolutionary stasis in an extant
vertebrate despite tens of
millions of years of divergence
African butterfly fish (Pantodon) lineages that split more than
50 million years go, but have
