Transcript Saving Species

Saving Species
What does it take to save rare
species from extinction?
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!
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
Population Size
• How big must a population be to be “saveable?”
• “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)
Desert Bighorn Sheep
Figure 3.1 in Primack – How
big do populations of Bighorns
need to be for long-term
survival?
(figure from Berger 1990)
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
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
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
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
Bald Eagle
Threat: DDT
http://www.npca.org/wildlife_protection/wildlife_facts/
baldeagle.html
The Great Whales
Threat: Over-hunting
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
African Elephant
Fig. 3.8 in Primack – What habitat area appears to be
necessary for long-term survival in this species?
Hawaiian Monk Seal
Primack Fig. 3.7 - What human
impact was removed to improve
Monk Seal habitat?
Northern Spotted Owl
A famous example of how hard it
can be to set aside habitat for the
preservation of a species…
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
Peregrine Falcon
A famous success
story – initial
threat: DDT;
Habitat: abundant!
California Condor
Population declined
in wild to 22
individuals; after
captive breeding now
up to 289. Visit the
site linked below…
http://www.fws.gov/hoppermountain/cacondor/condormanagement.html
Whooping Crane
Video clip…
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.
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…
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.