ENVS 10

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ENVS 10

• Lecture 8
• Extinction Crisis

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Speciation

• Speciation the creation of new species through
  the process of natural selection

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What is Extinction?

• Local extinction a species is no longer found in
  a portion of its range
• Ecological extinction so few members of a
  population are left that it can no longer serve
  its purpose in the ecosystem
• Biological extinction a species is no longer
  found anywhere on earth

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What are endangered, threatened, and rare species?

• Endangered a species in danger of becoming
  extinct over all or most of its natural range
• Threatened a species in danger of becoming
  endangered in the near future
• Rare species that are limited in their
  distribution

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What causes species to become threatened,
endangered, or extinct?

• No longer adapted for survival under current
  conditions (natural cause)
• Habitat loss
• Habitat fragmentation
• Hunting and poaching
• Overfishing
• Extermination
• Invasion of non-native species

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Habitat Fragmentation and Subdivided Populations

• Population fragmentation

• Is the splitting and consequent isolation of
  portions of populations by habitat degradation
• Is one of the most harmful effects of habitat
  loss due to human activities

Figure 20.18
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Extinction

• Probably 500 million species have existed over
  time
• With the advent of agriculture species
  extinctions have increased dramatically
• 8000 b.c. to a.d. 1600, one species went extinct
  every thousand years
• In 1985 1000 species went extinct every year
• In 2000, between 20,000 and 50,000 species are
  considered doomed to extinction every year

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Is extinction natural?

• 99 of all of the species that have ever
  inhabited the earth are extinct
• There are natural rates of extinction
  Background rate of species loss
• There have been 5 periods of mass extinction
  throughout history
• We are now in the worst extinction crisis in the
  last 65 million years!

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How does the current mass extinction differ from
past ones?

• Caused by one species--- Humans
• Occurring rapidly--- over decades rather than
  1,000s of years
• Destroying biologically diverse ecosystems
• Losing keystone species
• Losing highly adapted species

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Why care about species loss?

• Economic or Medical uses
• Scientific and Ecological reasons
• Aesthetics and Recreation
• Ethical reasons
• Extinction is forever

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Do we preserve individual species or their
habitats?

• Preserving individual species does not guarantee
  that they will survive in the wild if we dont
  also preserve their habitat
• Need an integrated approach

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Legal Protection of Endangered Species

• Federal Endangered Species Act
• California Endangered Species Act
• California Environmental Quality Act
• California Department of Fish and Game Code