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Extinctions
Who goes extinct?
When do they go extinct?
Why do they go extinct?
60%G 57%G
26%F 22%F
50%G
82%G
51%F
53%G
22%F
47%G
16%F
ammonites
*
brachiopods
Importance of Contingency
Some Clades Within a Lineage Do Better Than Others
ammonites: P/TR 2 lineages survive and re-radiate
K/T
all extinct
Ecological Roles Filled by Different Lineages; e.g., “Reefs”
~550 Cambrian calcified microbes; archeocyanthans (sponge-like)
~450 Ordovician
~250 Permian
bryozoans; stromatoporoids; sponges
scleractinian corals
???
and maybe the end-Permian mass extinction:
Basu et al. 2003 Science 302:1388
What Enhances Survival During a Mass Extinction Event?
Jablonski 1986; Jablonski and Raup 1995
end-Cretaceous
most recent, best fossil record
bivalves, gastropods
is survival random ?
do traits which enhance survival during non-mass extinctions
also affect survival during mass extinction events?
larval feeding ecology affects background extinction rates of species
long-lived clades have broad geographic ranges
body size does not affect the probability of survival
geographically widespread taxa are less likely to become extinct
Contingency plus Opportunity
Mammals replaced dinosaurs
Lineage replacement may be either passive or competitive
one lineage becomes extinct,
another radiates
one lineage causes
the extinction of
another
dinosaurs, mammals
angiosperms, conifers;
horses in NA only
bivalves, brachiopods are an example of competitive replacement
enhanced by a mass extinction event
Extinctions
Africa/Eurasia
Few extinctions. In Africa ancient
In Eurasia mammoths, mastodons, wooly rhinos
Australia (~40,000BP)
Essentially all large mammals. 4 large species remained.
Giant koalas, giant (hippo-sized) Diprotodon, giant
kangaroos, giant wombats. 45 large species. 90%+
extinct. Also giant lizards, tortoises, snakes and large,
flightless birds
North/South America (~12,000BP)
Most extinguished.
Exceptions are also ice age migrants (deer, puma, bison,
caribou, moose, musk oxen). Mammoths, mastodons,
ground sloths, giant camels, bison, bears, wolves,
N. Am 33 genera S. Am. 46 genera (20 genera in
previous 3 million years)
New Zealand (~1000 yrs)
Moas, giant kiwis,
Essentially all large species
Madagascar (~1000 yrs)
Essentially all large
mammals and birds. Giant lemurs, Elephant birds
Africa
%loss of large mammals
14%
N. America
S. America
Australia
73%
79%
86%
Extinction happened at different times
It is always soon after the arrival of humans
Nobody else had invaded
Humans and extinction
Human invasion associated with widespread extinction
post-Pleistocene faunas of North America, northern Eurasia
megafauna of Australia
Avifauna of Pacific islands
Steadman 1995 Science 267:1123
examined bone deposits on 40 Pacific islands
bone deposits predate human colonization by tens of
thousands of years
two waves of human colonization
Polynesians 1000-3500 yrs bp
Europeans 100-300 yrs bp
Lanai
hookbill
Hawaiian rail
Bishop’s o’o
Black mamo
Laysan rail
Moa nalo
Extinction of the Polynesian avifauna
Hawaii (colonized ~500-600 A.D.)
endemic finches (honeycreeepers); flightless ducks, geese, ibis
60 endemic species extinct before European arrival
20-25 more extinctions in the last 200 years
New Zealand (colonized ~800-1100 A.D.)
endemic moas, kiwis, waterfowl
44 endemic species extinct within the last 1000 years
7 more extinctions in the last 200 years
Easter Island (colonized ~500-1000 A.D.)
complete deforestation 550 years b.p.
fossil evidence of 2 rails, 1 heron, 2 parrots, 1 owl (all extinct)
originally 25-30 nesting seabirds
8-10 species nest only offshore
13-16 species no longer nest anywhere nearby
1 species remains nesting on the main island
Galapagos Islands
not inhabited until European discovery in 1535;
minor human impact until ~1800 A.D.
0-3 vertebrate species extinct in 4,000-8,000 years << humans
21-24 extinctions since European discovery and human settlement
Reasons for Polynesian avifaunal extinction
habitat loss
human predation
introduced predators (pigs, dogs, rats, snakes)
introduced competitors (goats, mynahs*)
introduced pathogens (esp., avian malaria)
Steadman estimates that 10 species/populations lost from each of the
islands (n=800) ---> 8000 species, ~2000 species of rails
Mass extinctions represent rare events on a continuum of
extinction intensities
Lineages may be lost, may become rare, or may diversify as a consequence
of a mass extinction event
Recovery is characterized by:
1) initial interval of low diversity dominated by geographically widespread,
ecologically generalist species
2) expansion of opportunistic species
3) relatively rapid ecological diversification
Because they so greatly change species composition, subsequent lineage
diversification is not predictable but is contingent on which
clades survive
Heterogeneity in the recovery of molluscan faunas after the Cretaceous
mass extinction may reflect sampling error or ecological contingency
Humans are producing another mass extinction event, largely through
habitat destruction