Download - Saving Species
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Saving Species
What does it take to save rare species from extinction?
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Extinction Rates
• The Sixth Mass Extinction:– Current extinction rates are 100 times greater
than background– Previous mass extinction rates were between
about 5-10 times greater than background– Background rate: 1-2 species per year– Modern rate: 3 species per hour!
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Risks to rare species
• We know about the “extinction vortex” and the many threats faced by rare species
• If we agree that at least some of these rare species should be saved – it is our responsibility to try to do so – then…– We must protect populations in order to save species
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Population Size
• How big must a population be to be “save-able?”
• “Minimum Viable Population” (MVP) analysis– Definition: The smallest population size that
can be predicted to have a very high chance (e.g. 99%) of persisting into the foreseeable future (e.g. 1000 yrs)
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Desert Bighorn Sheep
Figure 3.1 in Primack – How big do populations of Bighorns need to be for long-term survival?
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(figure from Berger 1990)
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Habitat Size
• How big must the habitat area available be in order for a population to survive?
• “Minimum Dynamic Area” (MDA)– This will depend very much on the size of the
species and its territorial restrictions
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African Lions
• Large carnivores, such as lions, need huge areas to support viable populations
• Reserves of 10,000 km2 needed!
• To support small mammals in Africa, reserves of 100-1000 km2 necessary
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Multiple Ways to Preserve Rare or Endangered Species
• What approaches can you think of that might be necessary under different conditions?
• Retain or improve habitat (remove threats) – for some species this is enough
• Captive breeding with reintroduction into good habitat
• Off-site conservation
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Habitat Improvement or Preservation
• For some species, it is enough to simply remove an external threat that was driving population sizes down
• If the habitat is relatively intact, once the threat is removed the species will recover
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Bald Eagle
http://www.npca.org/wildlife_protection/wildlife_facts/baldeagle.html
Threat: DDT
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The Great Whales
Threat: Over-hunting
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Habitat Improvement or Preservation
• For other species, the main threat to their existence may be habitat loss or fragmentation
• Creating habitat reserves may be a successful way to help the species recover and maintain viable population sizes
• …but this is not always easy… (more on this topic next week); and it’s easier for the “charismatic mega-fauna” than for other species
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African Elephant
Fig. 3.8 in Primack – What habitat area appears to be necessary for long-term survival in this species?
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Hawaiian Monk Seal
Primack Fig. 3.7 - What human impact was removed to improve Monk Seal habitat?
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Northern Spotted Owl
A famous example of how hard it can be to set aside habitat for the preservation of a species…
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Captive Breeding for Reintroduction to the Wild
• In some cases, populations have been driven so low that there is no hope of a species surviving without human intervention (Wilson’s “100 Heartbeats Club”)
• Several examples of successful captive breeding programs
• BUT this can only work if measures have been taken to insure that the habitat is preserved or restored in preparation for re-release– Sometimes controversial
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Peregrine Falcon
A famous success story – initial threat: DDT; Habitat: abundant!
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California Condor
http://www.fws.gov/hoppermountain/cacondor/condormanagement.html
Population declined in wild to 22 individuals; after captive breeding now up to 289. Visit the site linked below…
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Whooping Crane
Video clip…
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Yellowstone Wolves
Often a species that is threatened in one part of its range can be reintroduced from another part of the range where it is still abundant.
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Off-Site Conservation
• Some species have declined to such low population levels, and they or their habitat are so threatened in the wild that the only way to preserve them is in captivity
• The species can be maintained in zoos, aquaria, botanical gardens, seed banks…
• Very expensive – only done as a last resort• Risk: may lose habitat in the meantime; for
some, they will never be reintroduced…
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Przewalski’s Horse
The last takhi seen in the Gobi region was in the 1960s. The 1,200 some horses alive today are descendents of 12 individuals captured and bred in zoos.