Post on 02-Jun-2018
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Vulnerability to Extinction
Prepared bySe Su Yan
Soh Yi Han
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Important Fact
Rare species are considered to be especially
vulnerable to extinction, while common species
are considered less so.
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Rare Species
1. A species may be considered rare if it
occupies a narrow geographic range.
Example:
Venuss flytrapoccurs only in the savannahs of
the coastal plain of the Carolinas
in eastern North America.
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2. A species may be considered rare if it
occupies only one or a few specialized
habitats.
Example:
Salt marsh cord grassis found only in salt
marshes and not in other habitats; yet within
this habitat, cord grass
is quite common.
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3. A species considered rare if it is found
only in small populations.
Example:
Mediterranean monk sealsare found overa wide area, but their populations are always
small and isolated.
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Which species are most vulnerable?
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Species with a very narrow
geographical range
Species with only one or a fewpopulations
Species in which population size issmall
Species in which population size isdeclining
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Species with low population density
Animal species with a large body size
Species that are not effectivedispersers
Seasonal migrants
Species that need a large home range
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Species with little genetic variability
Species with specialized nicherequirements
Species that are characteristicallyfound in stable, pristine environments
Species that form permanent ortemporary aggregations
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Species that have evolved in isolation
and have not had prior contact with
people
Species that are hunted or harvestedby people
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Species in which population size is
small
Population size by itself seems to be one of the best
predictors of the extinction rate of isolated populations.
Example:
Survival of bird species at the Bogor Botanical Garden in
Java, a woodland and arboretum that has been isolated for
50 years.
At this site, only 25% of the birds that had small population
sizes during the period from 1932 to 1952 survived into the
1980s, while species that were initially common survived.
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Species with low population density
Population densityindividuals per unit area
A species with a low population density will tend to have
only small populations remaining if its range is fragmented
by human activities.
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Animal species with a large body
size
Large animals tend to have
large individual range
Require more food
More easily hunted by humans
Example:
In Sri Lanka, the largest species of carnivores:
Elephants and deer are recently at the greatest risk of extinction
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Seasonal migrants
Species that migrate seasonally depend on two or more distinct
habitat types.
If either one of there habitat types is damaged, the species
may be unable to persist.
If barriers to dispersal are created between the needed
habitats by roads, fences, or dams, a species may be unable
to complete its life cycle.
Example:
Salmon species that are blocked by dams from swimming up
rivers and spawning are an example of this problem.
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Niche requirements
Once habitat is altered, the environment may no longer be
suitable for specialized species.
Example:
Wetland plants that require very specific and regular
changes in water level may be rapidly eliminated when
human activity affects the hydrology of an area.
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Species that form permanent /
temporary aggregations
Species that group together in specific places are highly
vulnerable to local extinction.
Example:
Bats forage widely, but typically roost together in particular
cavers. Hunters entering these caves during the day can
rapidly harvest every individual in the population.
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Crisis after Crisis for the
Black-Footed FerretFacts :
Several near-calamitous crises resulted from theextreme sensitivity of this species to disease.
Ultimately, the fact that the species still exists at all
is amazing, despite the efforts of so many wildlife
biologists working on the recovery plan.
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Experienced a dramatic decline in their North American range during the first half ofthis century, presumably due to agricultural development of their prairie habitat and
a deliberate, government-endorsed program by ranchers to kill off the prairie dog
(the ferrets main prey species). The black-footed ferret was first thought to beextinct in the late 1970s, when the only known wild population a small colony in
South Dakotadied out
Biologists with the United States Fish and Wildlife Service attempted a captive
breeding program. The experiment was a failure. More ferrets were taken from thewild and added to the captive population, but this group was apparently too closely
related to form a viable gene pool and compatible breeding pairs. Tumors and
diabetes, possibly related to inbreeding, killed several of the captive ferrets. With
the loss of both the captive and wild populations by 1979, the species was thought to
be completely extinct.
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A colony of 128 animals was located in Meeteetse, Wyoming. Fish and Wildlife Service tooversee ferret recovery, did not initially advocate another captive breeding program on
the groundsthat the wild population seemed to be surviving, no money or facilities had
been committed for a breeding program, and the previous attempt failed. Furthermore,administrative and policy disagreements among government departments and a private
consulting firm stalled recovery initiatives. New census data 1985 showed that thenumber of ferrets had dropped by 50 percent and the population was in immediate
danger of extinction.
At this point, biologists decided that drastic measures were required to save the ferret. All
remaining black-footed ferrets were to be captured, vaccinated, quarantined, and sent
to the Game and Fish Departments captive breeding center in Sybille, Wyoming. Onlytwo males were initially present among the captive ferret population, both relatively
young. Neither had ever mated before, and they showed no interest in the females during
the first breeding season. Through the serendipitous capture of an experienced adult male
in 1986, the Sybille biologists were able to coax the males to mate.
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Captive breeding led to a virtual population explosion among the ferrets.
Ferrets numbers were sufficient in 1991 to permit the release and on the year after.
However, only about 10 ferrets are still alive in the wild. The reasons for this for thisdrastic decline are not completely known, but are apparently due to attack by
predators such as coyotes and owls.
The combination of declining species numbers and habitat destruction, with extremesusceptibility to disease, compound by squabbling among government biologists and
private conservation groups, is a melancholy tale in which the black-footed ferret
keeps tottering at the brink of extinction.
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Conservation Categories
To mark the status of rare and endangered species for
conservation purpose, the International Union for the
Conservations of Nature (IUCN) and the world
Conservation Monitoring Centre (WCMC) established
10 conservation categories.
Species in categories 3, 4 and 5 are considered to be
threatened with extinction.
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1. Extinct
A species that is no longer known to exist
4. EndangeredSpecies that have a high risk of extinction in the wild in the
near future, and may become critically endangered.
3. Critically endangeredSpecies that have an extremely high risk of going extinct
in the wild in the immediate future
2. Extinctin the wild
The species exists only in cultivation, in captivity
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5. VulnerableSpecies that have a high risk of extinction in the wild in
the medium-term future, and may become endangered
7. Near threatened
The species is close to qualifying as vulnerable, but is not
currently considered threatened
6. Conservation-dependent
The species is not currently threatened, but is dependenton a conservation program, without which the species be
threated with extinction.
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9.Data deficient
Inadequate information exists to determine the risk ofextinction for the specie.
10. Not evaluated
The species has not yet been assessed for its threat
category
8. Least concernThe species is not considered near threatened or
threatended
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