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5/19/14
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Conservation Biology Chapter 59
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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
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Biodiversity Crisis
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Biodiversity Crisis • The majority of recent extinctions have
occurred in the past 150 years • Increased rate of extinction is worsening • Half of Earth’s plant species may be
threatened • 2/3 of vertebrate species could perish by
the end of this century
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Biodiversity Crisis • Majority of extinctions have occurred on
islands – Of 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
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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
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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
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Biodiversity Crisis
Some species under imminent extinction threat
Silversword
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Biodiversity Crisis
Hotspots: areas where species have high endemism and are disappearing at a rapid rate. Red areas are hotspots.
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Biodiversity Crisis
25 hotspots have been identified Contain nearly half of all terrestrial
species in the world
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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
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Biodiversity Crisis
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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
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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
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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
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Value of Biodiversity • Rosy Periwinkle:
vinvlastine and vincristine effectively treat common forms of childhood leukemia – Increase chances
of survival from 20% to over 95%
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Value of Biodiversity
Cancer-fighting drugs like taxol, have been developed from the bark of the Pacific yew
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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
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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
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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
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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
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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 ?
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Factors Responsible • Causes of extinction: direct or indirect
– Overexploitation – Habitat loss – Introduced species – Disruption of ecosystem interactions – Pollution – Loss of genetic variation – Catastrophic disturbances
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Factors Responsible
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Factors Responsible • Habitat loss devastates species
richness • Natural habitats may be adversely
affected by humans 1. Destruction 2. Pollution 3. Disruption 4. Habitat fragmentation
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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
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Rain forest covering the eastern coast of Madagascar: • 90% habitat loss • many extinctions • 16 of 31 primate species threatened or extinct
Factors Responsible
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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
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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
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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
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Factors Responsible
• Fragmentation of Wisconsin woodland habitat
• Cover less than 1% of original area
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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
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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
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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
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Factors Responsible • Human influence on colonization
– Plants and animals can be transported in the ballast of large ocean vessels
Zebra mussels
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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
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Factors Responsible
Two thirds of Hawaiian birds are extinct or have reduced populations
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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
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Factors Responsible • Efforts to combat introduced species
– Eradicating extremely difficult, expensive and time consuming
– Prevent introduction
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Factors Responsible Disruption of ecosystems can cause an extinction cascade
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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
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• 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
Factors Responsible
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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
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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
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Preserving Species Destroyed habitats can sometimes be restored
• Restore plants and animals to abandoned farm lands
• No restoration is ever truly pristine
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Preserving Species Removing introduced species • Cichlid fishes restoration
– Breeding and restocking endangered species
– Removal of water hyacinth and Nile perch populations
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Preserving Species Cleanup and rehabilitation • Clean up pollution • Nashua River in New England
– Heavily polluted habitat – Returned to near pristine condition
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Preserving Species
Case Study: Peregrine falcon
• DDT banned in 1972 – Captive breeding
program began in 1970
– 1986: over 850 birds released in 13 states
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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
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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
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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
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Conservation of Ecosystems