Download Causes of extinction

Conservation Biology
Chapter 59
1
Biodiversity Crisis
• Extinction is a fact of life: all species
become extinct eventually
• More than 99% of species known to
science are now extinct
• Current accelerating loss of habitat
– 20% of present day species will be
extinct by the middle of this century
– 2000 of the world’s 8600 species of
birds could go extinct
2
Biodiversity Crisis
• Members of Homo
sapiens wreaked havoc
even in prehistoric times
• Mammoths and
mastodons, giant sloths,
saber-toothed tigers
• 74% - 86% of mega
fauna thought to have
been caused by human
hunting
3
Biodiversity Crisis
• 40,000 years ago Australia had mega
sized marsupials
– All disappeared at about the same
time humans arrived
• Madagascar human caused extinctions
– 15 species of lemurs
– Pigmy hippopotamus
– Flightless elephant bird (3m tall), 13
species of moas, and more
4
Biodiversity Crisis
Why have African mega fauna survived ?
• Perhaps because animals coevolved with
humans there
• Animals evolved counteradaptations to
human predation
5
Biodiversity Crisis
• The majority of recent extinctions have
occurred in the past 150 years
• Increased rate of extinction is worsening
• Birds recognized as critically endangered
increased from 8% in 1996 to 2000
• Half of Earth’s plant species may be
threatened
• 2/3rds of vertebrate species could perish by
the end of this century
6
Biodiversity Crisis
• Majority of extinctions have occurred on
islands
– 85 species of mammals; 60% lived on
islands
• Why are islands so vulnerable ?
– Evolved in the absence of predators
– Humans introduced competitors,
diseases
– Island populations are usually small
which increases their risk for extinction
7
Biodiversity Crisis
• Current mass extinctions are notable
because
– It is the only such event triggered by a
single species (Homo sapien)
– A few million years is a long time to wait
for recovery
– It is not clear that biodiversity will
rebound this time
• Humans are utilizing resources that new
species would need to evolve
8
Biodiversity Crisis
• Endemic species: species found
naturally in only one geographic area
and no place else
– Occupy restricted ranges
– Example: Komodo dragon lives only
in a few islands
– Example: Mauna Kea Silversword
only lives in a single volcano crater on
the island of Hawaii
9
Biodiversity Crisis
Silversword
Some species under imminent extinction
threat
10
Biodiversity Crisis
Hotspots: areas where species have high
endemism and are disappearing at a
rapid rate. Red areas are hotspots.
11
Biodiversity Crisis
25 hotspots have been identified
Contain nearly half of all terrestrial
species in the world
12
Biodiversity Crisis
• Human population growth in hotspots
• By protecting 1.4% of the world’s land
surface
– 44% of the worlds vascular plants
– 35% of its terrestrial vertebrates can be
preserved
• In 1995, 20% of the human population
were located in hotspots
• Growth rate exceeds the average in 19
hotspots
13
Biodiversity Crisis
14
Biodiversity Crisis
Why are species going extinct in hotspots ?
• High rates of habitat destruction
– Land cleared for agriculture, housing,
economic development
• More than 70% of the original area of each
hotspot has already disappeared
• Only 15% or less of original habitat remains
in 14 hotspots
– 90% Madagascar forest lost
– 95% Brazilian forest lost
15
Value of Biodiversity
• Why care about loss of biodiversity ?
– Direct economic value of products we
obtain from species: food and drugs
– Indirect economic value of benefits
produced by species without our
consuming them
– Ethical and aesthetic values
16
Value of Biodiversity
• Direct economic value includes
resources for our survival
– Food crop genetic variation
– 40% of prescription and
nonprescription drugs have active
ingredients extracted from plants
• Aspirin
• Cancer fighting drugs
17
Value of Biodiversity
• Rosy Periwinkle:
vinvlastine and
vincristine
effectively treat
common forms of
childhood leukemia
– Increase chances
of survival from
20% to over 95%
18
Value of Biodiversity
Cancer-fighting
drugs like taxol,
have been
developed from
the bark of the
Pacific yew
19
Value of Biodiversity
• Indirect economic value is derived from
ecosystem services
– Maintain chemical quality of natural
water, buffer against storms and droughts
– Prevent loss of minerals and nutrients
– Moderate local and regional climate
– Absorb pollution
– Promote breakdown of organic wastes
and cycling of minerals
20
Value of Biodiversity
Mangroves in
Thailand are
more
Valuable than
Shrimp farms
21
Value of Biodiversity
Tropical
rainforests provide
more economic
benefits if they are
left standing than
if they are
destroyed and the
land used for other
purposes
22
Value of Biodiversity
Case Study: New York City watershed
• 90% of 9 million people’s water comes from
the Catskill Mountains and Delaware River
• Dilemma: Protect functioning ecosystem or
construct filtration plants
– To build plants cost $6 billon
– Operating cost $300 million/year
– Spend $1 billion over 10 years to
preserve the ecosystem
23
Value of Biodiversity
New York City’s water source
24
Value of Biodiversity
• Economic trade-offs
– Ecosystem was beneficial when the United
States was being settled
– Habitat destruction today may be
economically desirable
• How many services will it provide
• What are the negative effects
–Increased flooding and pollution
–Decreased rainfall
–Vulnerability to hurricanes
25
Value of Biodiversity
• Consequences of removing a species
could mean we are gambling with the
future of an ecosystem we depend on
• Problems of valuing ecosystems
– Do not have a good estimate of the
monetary value of services provided by
ecosystems
– People who gain the benefits of
environmental degradation are often not
the same people who pay the costs 26
Value of Biodiversity
• Ethical and aesthetic values are based
on our conscience
– Every species has a value of its own
– Humans should act as guardians or
stewards for the diversity of life
around us
– How do we place a value on beauty ?
• What if it no longer existed ?
27
Value of Biodiversity
28
Factors Responsible
• Causes of extinction: direct or indirect
– Overexploitation
– Habitat loss
– Introduced species
– Disruption of ecosystem interactions
– Pollution
– Loss of genetic variation
– Catastrophic disturbances
29
Factors Responsible
• Case Study: Amphibians on the decline
• 1963, Jay Savage Costa Rica
– Many breeding toads, bright orange
• Bufo periglenes
• 1989, only a single male was observed
• Today, no toads
• They have gone
extinct
30
Factors Responsible
31
Factors Responsible
• Frogs in trouble
– Frog populations that had once been
abundant were now decreasing or
entirely gone
– 2005: 43% of amphibian species
experienced decreases in population
size
– 1/3rd are threatened with extinction
32
Factors Responsible
33
Factors Responsible
Why worry about amphibian declines ?
1. Many species have declined in pristine,
well-protected habitats
2. Particularly sensitive to the state of the
environment because of their moist skin
• Chemicals pass into their body
• Larval habitats are aquatic
34
Factors Responsible
3. No single cause for amphibian decline
is apparent
– Different species are afflicted by
different problems
– Global environment is deteriorating
in many different ways
35
Factors Responsible
•
Habitat loss devastates species
richness
• Natural habitats may be adversely
affected by humans
1. Destruction
2. Pollution
3. Disruption
4. Habitat fragmentation
36
Factors Responsible
• Destruction of habitat
– Clear-cut harvesting of timber
– Burning of tropical forests
– Urban and industrial development
• 10 fold increase in habitat area leads to
~ doubling in the number of species
• Area reduced by 90% then half of all
species will be lost
37
Factors Responsible
Rain forest
covering the
eastern coast of
Madagascar:
• 90% habitat loss
• many extinctions
• 16 of 31 primate
species threatened
or extinct
38
Factors Responsible
Extinction and Island Area
39
Factors Responsible
• Pollution
– Species can no longer survive
– Aquatic environments particularly
vulnerable
– Many lakes “sterilized” by acid rain
• Disruption
– Visitors to bat cave: four visits per
month caused 86% - 95% declines in
population size
40
Factors Responsible
• Habitat fragmentation: dividing the
habitat up into small, unconnected
areas
– Low population numbers
– Smaller populations in each fragment
– Edge effects: changes in
microclimate along the edge of a
habitat
41
Factors Responsible
• Edge effects
– Trees exposed to more sunlight
• Hotter and drier conditions
• Less biomass growth
– Opportunities for parasite and
predator species
– Habitat fragmentation is blamed for
local extinctions in a wide range of
species
42
Factors Responsible
• Fragmentation of Wisconsin woodland
habitat
• Cover less than 1% of original area
43
Factors Responsible
• Landowners in Manaus, Brazil
preserved patches of rain forest of
different sizes to examine the effect of
patch size on species extinction
• Extinction rate was negatively related to
patch size
• Even the largest patches (100 hectares)
lost half of their bird species in less than
15 years
44
Factors Responsible
Manaus, Brazil
45
Factors Responsible
Case Study: songbird declines
• Year round residents prosper (robins)
• Migrant songbirds have declined
– Nest in northern forests in summer
but spend winter in South or Central
America or the Caribbean Islands
– Rock Creek Park in Washington, DC
lost 90% in the past 20 years
46
Factors Responsible
• Nation wide, American redstarts
declined about 50% in 10 years
• Only about has as many birds fly over
the Gulf of Mexico each spring as in the
1960’s
• Culprit:
– habitat fragmentation and loss
– Availability of winter habitat declined
47
Factors Responsible
American Redstart
48
Factors Responsible
Case Study:
whales
• Over fishing
• IWC regulates
commercial
whale hunting
• Was it too late ?
49
Factors Responsible
Introduced species threaten native species
and habitats
• Colonization: process by which a species
expands its geographic range
– Birds are blown off course
– Bird eats a fruit and defecates its seeds
miles away
– Lowered sea levels connect to isolated
populations
50
Factors Responsible
• Colonization brings together species with
no history of interaction
• Ecological interactions may be strong
because species have not evolved ways of
adjusting to the presence of one another
• Results:
– Increase in species diversity
– Extinction of species
51
Factors Responsible
• Human influence on colonization
– Plants and animals can be
transported in the ballast of large
ocean vessels
Zebra mussels
52
Factors Responsible
• 50,000 species have been introduced in the
United States
• Effects:
– $140 billion per year in economic costs
– Human health: west nile fever
– Hawaii: mosquitoes brought malaria
• 70% native fauna extinct or restricted to
high elevations
53
Factors Responsible
Two thirds of Hawaiian birds are extinct or
have reduced populations
54
Factors Responsible
• Effect may not be direct, but spread
through the ecosystem
– Argentine ant has spread through
much of the southern US, reducing
populations of native ant species
• Negative effect on coast horned
lizard which feeds on native ants
• Native ants spread seeds,
introduced ones do not
55
Factors Responsible
• Efforts to combat introduced species
– Eradicating extremely difficult,
expensive and time consuming
– Prevent introduction
• Case Study: Lake Victoria cichlids
– 300 species of cichlid fishes: most
extinct, endangered or threatened
– Nile perch introduced in 1954
56
Factors Responsible
• How did cichlid extinctions occur?
– Eutrophication, algal bloom, cichlid
populations increased, oxygen levels
dropped
– Nile perch populations increased as
cichlids populations increased
– Nile perch ate many of the cichlids
– Introduction of water hyacinth
compounded the problem
57
Factors Responsible
Disruption of
ecosystems
can cause
an extinction
cascade
58
Factors Responsible
• Loss of keystone species may disrupt
ecosystems
– Sea otters are a keystone species of kelp
forest ecosystems
– Keystone species is a qualitative concept
– Flying fox bats are a keystone species
• Pollinates plants
• Key disperser of seeds
• Elimination due to hunting and habitat
loss is having a devastating effect
59
Factors Responsible
• Small populations are vulnerable to
extinction
– Demographic factors
• Ill-equipped to withstand catastrophes
• Heath hen
–Once common in US: hunting
pressure eliminated all but 1
population
–Fire destroyed the preserve’s habitat
–Population ravaged by predators 60
Factors Responsible
Heath hen and dusky seaside sparrow
61
Factors Responsible
• Lack of genetic variability is a second
dilemma small populations face
– Genetic drift
• Populations lacking variation composed of
sickly, unfit or sterile individuals
• More genetically variable individuals have
greater fitness
62
Factors Responsible
Case Study: Prairie chickens
• Was abundant in midwestern prairies
• 1837 introduction of agriculture in the
prairies; population has collapsed
• 1962 & 1967 sanctuaries established
– Privately owned grasslands disappeared
– 1990, egg hatching rate only 38%
– One dominant male: genetic variation
loss
63
Factors Responsible
• Tested genetic variation theory
– Extracted DNA for stuffed birds collected in
1930s
– Compared to birds living in the same place
before 1970 population collapse
– Genetic variation loss in population in
Illinois
– Transplant birds from other states
– Hatching rates back up to 94% in 1994
64
Factors Responsible
Prairie chicken, male mating ritual
65
Preserving Species
Destroyed habitats
can sometimes be
restored
• Restore plants and
animals to
abandoned farm
lands
• No restoration is
ever truly pristine
66
Preserving Species
Removing introduced species
• Cichlid fishes restoration
– Breeding and restocking endangered
species
– Removal of water hyacinth and Nile
perch populations
67
Preserving Species
Cleanup and rehabilitation
• Clean up pollution
• Nashua River in New England
– Heavily polluted habitat
– Returned to near pristine condition
68
Preserving Species
Case Study:
Peregrine falcon
• DDT banned in 1972
– Captive breeding
program began in
1970
– 1986: over 850
birds released in
13 states
69
Conservation of Ecosystems
• Habitat fragmentation is one of the
most pervasive enemies of biodiversity
conservation efforts
• Focus on preserving pristine state in
national parks and reserves
– Amount of land preserved is limited
– Not many areas completely protected
• Also focus on surrounding areas with
some level of human disturbance
70
Conservation of Ecosystems
• Key to management
– Operate them in a way compatible with
local land use
• No economic activity in core pristine
area
• Remainder of land used for
nondestructive harvesting of resources
• Some hunting
• Corridors of dispersal
71
Conservation of Ecosystems
• Corridors of dispersal
– Link pristine areas
– Increase population sizes
– Allow recolonization due to
catastrophe
– Protection to species that move over
great distances during the course of a
year
72
Conservation of Ecosystems
73