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Conservation Biology

Chapter 59

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Outline

• Overview of the Biodiversity Crisis• Species Endemism and Hotspots• Losing Biodiversity• Predicting Vulnerable Species• Factors Responsible for Extinction• Introduced Species• Ecosystem Disruption• Perils of Small Population Size• Preserving Endangered Species• Conservation of Ecosystems

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Overview of the Biodiversity Crisis

• More than 99% of all species known to science now extinct– ~ 20% of world’s biodiversity may be lost

during the next 30 years§ No more than 15% of the world’s

eukaryotic organisms have been discovered & given scientific names

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Overview of the Biodiversity Crisis

• Extinction due to prehistoric humans– Shortly after humans arrived, 74-86% of

megafauna became extinct§ caused by hunting & habitat clearing

• Extinctions in historical time– Historical extinction rates: best known for

birds & mammals because their relatively large & well studied

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Overview of the Biodiversity Crisis

• Since 1600, 2.1% of known mammal species and 1.3% of known birds have become extinct– majority of historic extinctions have

occurred on islands

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Species Endemism and Hot Spots

• A species found naturally in only one geographic area is termed endemic

• Isolated geographical areas, such as oceanic islands, often have many endemic species– Notable hotspots of endemism are

Madagascar,eastern Himalayas, and Australia§ many experiencing high rates of habitat

destruction

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Population Growth in Hotspots

• By protecting just 1.4% of the world’s land surface, 44% of the world’s vascular plants and 35% of its terrestrial vertebrates can be preserved– In 1995, these spots contained 20% of the

world’s population– areas of intense commercial exploitation

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Losing Biodiversity

• Direct economic value– sources of food, medicine, clothing, etc..

§ gene prospecting• Indirect economic value

– ecological functioning such as water purification, flood buffering, erosion buffers, and mineral cycling

• Ethical & aesthetic value (stewardship)– valuable in its own right

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Extinction Crisis

• Factors responsible for extinction– overexploitation– introduced species– disruption of ecological interactions– pollution– loss of genetic variability– catastrophic disturbances

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Case Study: Amphibian Declines

• Monteverde Cloud Forest Preserve in Costa Rica– golden toads - Bufo periglenes

§ despite living in a well-protected ecosystem, species appears to have gone extinct

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Frogs in Trouble

• Cause for concern– Many amphibian spp. all over the globe declining– Amphibians particularly sensitive to environmental

contaminants due to moist skin– appears to be no single cause for decline

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Habitat Loss

• Natural habitats adversely affected by human influences in four ways:– destruction

§ clear-cut tree harvesting– pollution

§ habitat degradation– disruption

§ park visitors

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Habitat Loss• Habitat fragmentation

– fragmenting of population into unconnected patches..

– Edge effects can significantly alter microclimate near edge & may reduce appropriate habitat for many species§ Expanding edges opens up opportunities for

parasites & predators to invade new areas

Fragmentation of a Woodland Habitat

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Case Study - Songbirds

• many areas of eastern United States, >75% of tropical migrant bird spp. experienced a significant decline in population size

– habitat fragmentation & loss§ wooded summer nesting grounds§ domesticed pets (e.g. cats) in urban areas§ winter habitat in Central & South America

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Overexploitation

• Case study: whales– Commercial whaling began in 16th century &

reached its apex in early 20th century§ As whalers reduced numbers of one species,

they simply switched species.v In 1974, International Whaling Commission

(IWC) banned hunting on all blue, gray & humpback whales & nstituted partial bans on othersØ 1986 - worldwide moratorium

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Introduced Species

• Detrimental effects– Colonization & extinction as natural processes

§ Colonization may bring together species with no previous history of interaction

– Human influences§ Effects of introductions on humans has been

enormousv Nonnative species cost US economy $140

billion annually

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Human Influences

• Cause species extinction & habitat restrictions• Indirect effects

– food chain alterations• Efforts to combat introduced species

– eradication§ difficult, expensive, time consuming, &

potentially impossible– prevention

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Case Study - Introduced Species

• Lake Victoria – huge shallow freshwater sea in equatorial east Africa: home > 300 spp of cichlid fish

– Nile perch introduced in 1954§ made up 2% fish harvest fromlake until 1978

v Eutrophication: increased cichlid populations, which in turn triggered perch to begin eating large numbers of cichlidsØ most cichlids eliminated by 1986

see documentary: Darwin’s Nightmare

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Ecosystem Disruption

• Species often become vulnerable to extinction when their web of ecological interactions becomes disrupted

– sea otters off the Alaskan coast§ Commercial whaling initiated series of

changes that led to orcas feeding on sea otters, causing disastrous effects on kelp forests

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Preserving Keystone Species

• Keystone species are usually characterized by the strength of their impact on their community– community importance

§ flying foxes§ sea urchins§ sea otters§ killer whales§ sea stars

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Perils of Small Population Size

• Demographic factors– By nature of their small size, small populations:

ill equipped to withstand a catastrophic event§ dusky seaside sparrow§ chances for extinction

• Lack of genetic variability– Small populations: prone to loss of genetic

variation as a result of genetic drift– Bottlenecking– Founder effect

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Case Study - Loss of Genetic Variation

• Greater prairie chicken in Illinois: undergone a population collapse over last six decades

– Introduction of steel plow in 1837 allowed large areas of prairie to be cleared§ Sanctuaries set-up in 1962 & 1967:

by 1980, wild populations extinct & sanctuary populations in troublev lost 33% of genetic diversity

Ø influx of genetic diversity reversing trends

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Preserving Endangered Species

• Preservation approaches:– habitat restoration– pristine restoration– removal of introduced species– cleanup & rehabilitation– captive breeding

§ peregrine falcon§ California condors§ Yellowstone wolves

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Conserving Ecosystems

• Isolated patches of habitat lose species much more rapidly than large areas– Megareserves: large areas of land

containing a core of one or more undisturbed habitats§ focus on preserving intact ecosystems

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Megareserve Design

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Summary

• Overview of the Biodiversity Crisis• Species Endemism and Hotspots• Losing Biodiversity• Predicting Vulnerable Species• Factors Responsible for Extinction• Introduced Species• Ecosystem Disruption• Perils of Small Population Size• Preserving Endangered Species• Conservation of Ecosystems