Download Extinction and Vulnerability to Extinction

Lecture 7
Biology 5865 –
Conservation Biology
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 (In Groom et al. 21006)
From Conservation Minnesota Magazine – Winter 2009
The U.S. Fish and Wildlife Service
estimates that expenditures for wildlife
watching are equivalent to the revenues
generated from all spectator sports,
amusement parks and arcades, non-hotel
casinos, bowling centers and skiing
facilities combined. Minnesota is no
exception.
Wildlife watching in Minnesota in 2006
generated an estimated $699 million in
retail sales, $1.25 billion in total economic
activity, 14,461 jobs, and over $94.6
million in state and local tax revenue.
http://library.fws.gov/nat_survey2006_economics.pdf
Science 307, 646, 2005.
Hawaiian Monk Seal
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 of the Peregrine Falcon
•Last survivor, Martha,
died in the Cincinnati
zoo in 1914
•Why – hunting, egg
collecting, habitat loss
Extinct United States Birds
Labrador Duck –
extinct 1878,
Over-harvesting eggs
and feathers
Extinct – 1904
habitat loss –
hunting for
feathers
Great Auk – extinct
1844, hunted for eggs
and down
Heath Hen – extinct
1932 – hunting,
predation of nests
Extinction – What is the issue?
• Tremendous loss of species over the past
400 years
• Thousands, if not tens of thousands, of
species are predicted to go extinct in the
coming decades (Millennium Ecosystem
Assessment 2005)
• Present rate of extinction is 100 and
perhaps 1000 times faster than the
present rate of speciation
• Unknown consequences for the future and
lost opportunities
Worldwide – Species with “Known” Extinctions since 1600
those currently “Threatened with Extinction”
Data compiled from Hunter (2002, p.126) & Primack (2010, p. 140).
Threat Proportion
Known
of of Species
Extinct Extinction Threatened
Mammals
Birds
Reptiles
Amphibians
Fish
Freshwater mussels
Flowering plants
87
1464
27%
131
2065
21%
22
622
8%
5
2279
36%
92
1722
6%
303
?
?
83
9115
4%
United States – Review of Current Status (past 150 years) of
Selected Groups of Animals and Plants
Presumed Possibly Critically
extinct
extinct imperiled
Mammals
1
0
8
22
3
27
Reptiles
0
0
7
Amphibians
1
1
21
Freshwater fish
16
1
91
FW mussels
17
20
73
Flowering plants
11
126
1,031
Birds
From Stein et al. Precious Heritage. (2000)
What is the status in Minnesota?
- From MN DNR web site
Special
Endangered Threatened concern Total
All species
96
101
242
439
Plants
57
66
133
256
Birds
7
6
15
28
Mammals
0
1
14
15
Fish
0
1
20
21
Mussels
8
12
15
25
Reptiles & amphibians
2
3
9
14
“Background” Extinction Rates
- from Groom et al. (2006)
• Prior to human dominance on Earth, background
rate of extinction (all species) is estimated to
have been about 0.1 to 10 species per year
• During mass extinctions, rate was 1-2 orders of
magnitude greater – hence, perhaps 1 to 1000
species per year
• Yet, these are based on the fossil record of
marine organisms – unknown whether they can
be applied to terrestrial organisms
Prediction of Extinction Rates
– the Species-Area Model
• From E.O. Wilson (1992) – The Diversity of Life, Belknap
Press, Cambridge, MA.
• Assumes that there is a relationship between number of
species and area of habitat - species/area effect
• Species/area effect estimated by S =CAZ
• S = number of species, A = Area, C is a constant (yintercept) that varies depending on the size of the area,
and Z is a constant that measures the slope of the line
relating S and A
Extinction Rate – Species/Area - 2
• Alternative equation
– log S = (log C) + z (log A)
– basically the equation of a straight line
• Z values often range between 0.15 and 0.35 based
on a variety of previous studies
• A Z value of 0.30 translates into a simple rule of
thumb
– if the area is reduced by 90 % then the number of species it
supports will be halved (Fig. 7.10 in Primack 2006)
• Wilson then chose the rate at which tropical forest
habitats are decreasing - he chose 1.8 % per year
(from Myers 1989)
Extinction Rates Species/Area - 3
• With different z values:
1. z = 0.30, then 0.54 % species lost per year,
2. z = 0.35, then 0.63 % species lost per year, and
3. z = 0.15, then 0.27 % species lost per year
• Wilson then used “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!!!!
From Groom et al. (2006)
Extinction Rate – Species/Area - 4
•
Analysis assumes – (neither of which is probably reasonable)
– species have broad geographic ranges - those with small
geographic ranges may be eliminated earlier, and
– 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
Extinction Rates – Direct Observation – from
Groom et al. (2006)
• 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
Extinction Rate – Direct Observation - 2
• 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
“we estimate that 6300 affiliate species are “coendangered”
with host species currently listed as endangered. Current
extinction estimates need to be recalibrated by taking
species coextinctions into account.”
“If a species is at risk of extinction, its close relatives
have a higher than average chance of being at risk”
Not on web site
Mass Extinctions and Global Change
• Estimates from the fossil record indicate
that about 99.9% of all species that have
ever lived have gone extinct
• Extinction has been a constant process
over the 3.5 billion year history of life on
earth
End of the Pleistocene (about 11,000 ybp)
33 genera went extinct in less than 1000
years in North America - the cause ?
1. Over hunting by humans crossing over
from Siberia to Alaska, or
2. Significant and rapid climate change
Island Species
- read Song of the Dodo – by Quammen
Species are particularly vulnerable to extinction –
many examples in Primack (2010)
• 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
Defining Extinction
• Extinction is hard to define - e.g., cahow is a 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)