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Introduction to Wildlife & Fisheries Conservation
WFSC 304
Lecture 9: Vulnerability to Extinction
Defining Extinction
• Extinction is hard to define
• Rule of thumb is that a species is extinct after no evidence of it exists for 50 years
• Cahow—rare seabird thought to be extinct since 1621, but rediscovered in 1906
and a breeding colony discovered in 1951 (Hunter, 2002)
• Ivory-billed Woodpecker - may be extinct in North America but a few may be
surviving in pine forests of eastern Cuba, Arkansas, Florida. Not seen since
1950 but potential sighting in Arkansas in 2004.
• Basic problem in extinction rates is that most species have never been described
“centinelan extinctions” according to Wilson (1992)
• Even so, we know that a large fraction of defined species are vulnerable:
Suppose a taxon is vulnerable. What does the conservation biology groundwork to
prevent extinction look like? Tapir case study here (Patrícia Medici TED talk; 11:32)
baby tapir
Part of extinction vulnerability is low population size and endemism (go hand in
hand). Here is a look at the number of endemic plants reported by state.
Geological record of extinctions
 Nearly all species that have
ever lived have gone extinct
 Extinction has been an everpresent but dynamic process over
the 3.5 billion year history of life
on earth
 5 major ancient crashes
 Plus a 6th (current) crash
Cause of 5 major ancient extinction waves?
We basically still don’t know, but the meteor hypothesis isn’t very strong:
Wikipedia: Marine regression is a geological process occurring when areas of
submerged seafloor are exposed above the sea level. The opposite event, marine
transgression, occurs when flooding from the sea covers previously exposed land.
Evidence of marine regressions and transgressions occurs throughout the fossil
record, and these fluctuations are thought to have caused or contributed to
several mass extinctions, among them thePermian-Triassic extinction event (250
million years ago) and Cretaceous–Paleogene extinction event (66 Ma). At the time
of the Permian-Triassic extinction, the largest extinction event in the Earth's
history, global sea level fell 250 m (820 ft).
#6: Late Pleistocene/Anthropocene (about 11,000 ybp)
 33 genera went extinct in less than 1000 years in North America
 Very clearly demarcated—terrestrial vertebrates over 97#
 Similar extinctions in Europe, Asia and Australia
 Some causes discussed in Science Daily article
 Cause?
o Probably: Over hunting by humans
 Extinction took place in NA at precisely the
time humans entered and spread (13.8-11
 Speartips (see 3rd and 7th papers on my
website) found in many megafauna
o Possibly (or exacerbated by): Rapid climate change
Good video on extinction topic here (9:11)
Good article on mammoth extinction:
Interesting megafauna tangent—giant arctic camels evolve in NA, later go extinct
here but descendants adapt to desert: Nat. Geogr. article
The North American
Megafauna was huge and
wild. Giant beavers, actual
lions (larger than those in
Africa), rhinos, etc.
Tasmanian wolf/tiger
Extinct @ 1900
Video from last zoo captives
Both sexes have pouch
 Its climate and geological diversity have given rise to a highly diverse group
of animals and plants, while isolation has resulted in 70-90 % of all its plants
and animals are endemic to the island
 Its ecosystems are highly degraded, its human population rapidly expanded
from 2.5 million in 1900 to 12 million in 1990
 Conservationists are closely watching Madagascar because there are so
many endemic species to be lost but many efforts are on-going to
1. protect some ecosystems,
2. foster ecotourism,
3. encourage sustainable development, and
4. improve land use practices