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Conservation Biology Chapter 59 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

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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

  • 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


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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


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Biodiversity Crisis

Why have African mega fauna survived ?

  • Perhaps because animals coevolved with humans there

  • Animals evolved counteradaptations to human predation


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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


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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


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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

Silversword


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Biodiversity Crisis (Cont.)

Some species under imminent extinction threat


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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

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

Mangroves in

Thailand are more

Valuable than

Shrimp farms


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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

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


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Value of Biodiversity

New York City’s water source


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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

  • 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



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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





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Factors Responsible

Why worry about amphibian declines ?

  • Many species have declined in pristine, well-protected habitats

  • Particularly sensitive to the state of the environment because of their moist skin

    • Chemicals pass into their body

    • Larval habitats are aquatic


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Factors Responsible

  • No single cause for amphibian decline is apparent

    • Different species are afflicted by different problems

    • Global environment is deteriorating in many different ways


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Factors Responsible

  • Habitat loss devastates species richness

  • Natural habitats may be adversely affected by humans

    • Destruction

    • Pollution

    • Disruption

    • 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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Factors Responsible

Rain forest covering the eastern coast of Madagascar:

  • 90% habitat loss

  • many extinctions

  • 16 of 31 primate species threatened or extinct


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Factors Responsible

Extinction and Island Area


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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

Manaus, Brazil


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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


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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


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Factors Responsible

American Redstart


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Factors Responsible

Case Study: whales

  • Over fishing

  • IWC regulates commercial whale hunting

  • Was it too late ?


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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

  • Case Study: Lake Victoria cichlids

    • 300 species of cichlid fishes: most extinct, endangered or threatened

    • Nile perch introduced in 1954


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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


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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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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


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Factors Responsible

Heath hen and dusky seaside sparrow


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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

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


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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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Factors Responsible

Prairie chicken, male mating ritual


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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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