Download Lecture 08 - Extinction

Introduction to Wildlife & Fisheries Conservation
WFSC 304
Lecture 8: Extinction
Extinction
Extinction is the most irreversible and tragic of all environmental calamities.
With each plant and animal species that disappears, a precious part of creation is
callously erased.
—M. Soule, 2004
Time Magazine:
Hawaiian and Mediterranean monk
seals are endangered and at risk of
extinction with populations dipping
below 1,200 and 500 individuals,
respectively.
Recovery efforts successful for
many charismatic birds of prey,
such as the peregrine falcon,
osprey and bald eagle, who had
been impacted by habitat
modification, hunting and DDT.
Passenger pigeon
Thorough account here
• Once the most abundant bird in N.
America and perhaps the world.
• Invaluable asset to the first
Americans and the colonists.
• Hunted by game seekers
• Slaughtered by farmers
• Extinct in the wild by 1900 and in
captivity in 1914
• Congressman John F. Lacy (1900):
“We have given an awful exhibition
of slaughter and destruction, which
may serve as a warning to all
mankind. Let us now give an example
of wise conservation of what remains
of the gifts of nature.”.
• That year Congress passed the
Lacey Act, followed by the tougher
Weeks-McLean Act in 1913 and, five years later, the Migratory Bird Treaty Act
(Audubon 2014). Interesting that our most shameful act of slaughter inspired the
first protective measures.
• An NGO is planning to recreate the species using genetic technology (like Jurassic
Park). Good idea?
Many birds have gone extinct due to desire for meat (understandable?) but also
for feathers. Yes, really. Bird feathers make really cool hats and these were all
the rage for decades from the 1890s to 1913. Ended by grassroots movement
begun by two women in Boston
Extinct United States Birds Extinct – 1904 habitat loss – hunting for feathers
Labrador Duck – extinct 1878
(over-harvesting eggs, feathers)
Great Auk – extinct 1844 (eggs and down)
Heath Hen – extinct 1932 (hunting, predation of nests)
Carolina parrot – extinct (1904; 1918) (slaughter, habitat
loss)
Endemic species (e.g. on islands)
particularly vulnerable to loss
• Extinction of 11 species of moas
(large flightless birds) by the
Maoris in New Zealand
• Hawaiian islands - 44 species of
endemic land birds out of 82 went
extinct between the arrival of
Polynesians and the Europeans - probably a combination of habitat changes,
disease, and over hunting
• Extinction of ALL of Guam’s native birds due to introduced brown tree snake
Extinction stats
• Tremendous loss of species over the past 400 years
• Tens of thousands, of species are predicted to go extinct in the coming decades
(Wilson 1992, as discussed below; Millennium Ecosystem Assessment 2005)
• Present rate of extinction is 100 to 1000 times faster than the present rate of
speciation
• Unknown consequences for the future and lost opportunities
Prediction of Extinction Rates
The Species-Area Model
From E.O. Wilson (1992) – The Diversity of Life, Belknap Press, Cambridge, MA.
 Uses the well-known relationship between number of species and habitat
area
 Species per unit area estimated by:
S =CAZ
 Where S = number of species, A = Area, C is the y-intercept and Z is a
constant that measures the slope of the line relating S and A
 Wilson wanted to predict extinction rates from known data
 Alternative form:
log S = (log C) + z (log A)
(basically the equation of a straight line in log space)
 Z values often range between 0.15 and 0.35 based on a previous studies
 A Z value of 0.30 translates into a simple rule of thumb
o if the area is reduced by 90 %, the number of species it supports will be
halved (Fig. 7.10 in Primack 2006)
 Wilson then noted the rate at which tropical forest habitats are decreasing
o 1.8 % per year (from Myers 1989)
 With different z values:
o 1.z = 0.30, then 0.54 % species lost per year,
o 2.z = 0.35, then 0.63 % species lost per year, and
o 3.z = 0.15, then 0.27 % species lost per year
 Wilson used the “conservative” estimate of 0.27 % species lost per year and
multiplied this by a “conservative” estimate of the number of species in the
tropical forests - 10,000,000 species
 Result is 0.27 x 10,000,000 = 27,000 species going extinct per year!!!!
 So even if we assume he is overestimating by an order of magnitude, is it
worth sitting on our hands?
 Analysis assumes – (neither of which is probably reasonable)
o –species have broad geographic ranges - those with small geographic
ranges may be eliminated earlier, and
o –suitable habitat will remain within the ranges of most species
 Background or normal extinction rate is assumed to be about 1 to 10
species per year
 Estimated extinction rate in this example varies between 2700 to 27,000
times greater than the background extinction rate in tropical forests – is
this a mass extinction period?
 About 1,000,000 years is the “typical” life span of a species
 Note - tropical forests are estimated to contain one-half of the species on
Earth
IUCN (International Union for the Conservation of Nature) Red List documents
844 extinctions since 1500, a loss of 2.2 % of all evaluated species and 0.04 % of
all described species
 Certainly an underestimate because all species are not described
 Corrections made by using the best-known groups of species
For example, 100 birds and mammals have gone extinct between 1900-2000
•Hence, 15,333 species of birds and mammals – 0.65 % loss per century or 1 bird
or mammal species per year
•Compared with the historical record for birds and mammals – 0.0003 species per
year
•Hence, 333 times greater than background rate of extinction
Geological record of extinctions
 99.9% of 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 crashes
Cause of 5 major ancient extinction waves?
We basically still don’t know, but the meteor hypothesis isn’t very strong:
The latest wave of extinctions…
#5: Late Pleistocene (about 11,000 ybp)
 33 genera went extinct in less than 1000 years in North America
 Cause?
o Probably: Over hunting by humans newly arrived from Siberia
o Possibly: Rapid climate change
Defining Extinction
•Extinction is hard to define - e.g., cahow—rare seabird thought to be extinct since
last seen in 1621, but rediscovered in 1906 and a breeding colony discovered in
1951 (Hunter, 2002)
• Rule of thumb is that a species is extinct after no evidence of its existence after
50 years
• Consider the Ivory-billed Woodpecker - may be extinct in North America but a
few may be surviving in pine forests of eastern Cuba, Arkansas, Florida?; had not
been seen since the 1950's but potential sighting in Arkansas in 2004 – observation
under severe scrutiny and questionable
• Basic problem in extinction rates is that most species have never been described
- “centinelan extinctions” according to Wilson (1992)
The Sixth Extinction
Good video here (9:11)