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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