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1
Conservation BiologyChapter 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• 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
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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 as humans evolved
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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
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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
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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
Hotspots: areas where species have high endemism and are disappearing at a rapid
rate. Red areas are hotspots.
25 hotspots have been identifiedContain 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 CrisisWhy 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
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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...flooding, pollution, rainfall reduction
– 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
• 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 inThailand are moreValuable 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• 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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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
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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 ?
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
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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
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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
Extinction and Island Area
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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
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
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
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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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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
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Conservation of Ecosystems