Vulnerability to Extinction

8/11/2019 Vulnerability to Extinction

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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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Vulnerability to Extinction

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