Download Document

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
(more than 100lb) extinct
thought to have been
caused by human hunting
• 40,000 years ago Australia had mega sized
marsupials
– All disappeared at about the same time humans
arrived
3
Biodiversity Crisis
Why have African mega fauna survived ?
• Perhaps because animals coevolved with
humans there
• Animals evolved counteradaptations to
human predation as humans evolved
4
Biodiversity Crisis
• The majority of recent extinctions have
occurred in the past 150 years
• Half of Earth’s plant species may be
threatened
• 2/3rds of vertebrate species could perish
by the end of this century
5
Biodiversity Crisis
• Majority of extinctions have occurred on
islands
– 85 species of mammals extinct since
1600’s; 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
6
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
7
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
8
Biodiversity Crisis
Hotspots: areas where species have high
endemism and are disappearing at a rapid
rate. Red areas are hotspots.
25 hotspots have been identified
Contain nearly half of all terrestrial
species in the world
9
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
10
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
11
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...flooding,
pollution, rainfall reduction
– Ethical and aesthetic values
12
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
13
Value of Biodiversity
• Rosy Periwinkle:
vinvlastine and
vincristine
effectively treat
common forms of
childhood
leukemia
– Increase chances
of survival from
20% to over 95%
14
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
15
Value of Biodiversity
Mangroves in
Thailand are
more
Valuable than
Shrimp farms
16
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
17
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 18
Factors Responsible
• Causes of extinction: direct or indirect
– Overexploitation (historical problem)
– Habitat loss (major problem today)
– Introduced species (second today)
– Disruption of ecosystem interactions
– Pollution
– Loss of genetic variation
– Catastrophic disturbances
19
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
20
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
21
Habit area changes species
number
• In general 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
22
Factors Responsible
Rain forest
covering the
eastern coast of
Madagascar:
• 90% habitat loss
• many extinctions
• 16 of 31 primate
species
threatened or
extinct
23
Factors Responsible
Extinction and Island Area
24
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
25
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
26
Factors Responsible
• Fragmentation of Wisconsin woodland
habitat
• Cover less than 1% of original area
27
Factors Responsible
Case Study:
whales
• Over fishing
• IWC regulates
commercial
whale hunting
• Was it too late ?
28
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
29
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
30
Factors Responsible
• Human influence on colonization
– Plants and animals can be
transported in the ballast of large
ocean vessels
Zebra mussels
31
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
32
Factors Responsible
Disruption of
ecosystems
can cause
an extinction
cascade
• Loss of keystone species may
disrupt ecosystems
– Sea otters are a keystone
species of kelp forest
ecosystems
– Keystone species is a
qualitative concept
33
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
34
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 activity
35
Conservation of Ecosystems
36