"Unless something is done, and done quickly, one of the most interesting
survivals from the past still living on this earth will quickly follow
the Quagga
into extinction".
|
The Queenslander
newspaper, 25th Feb. 1932 (p. 43),
quoting G. W. Morey writing
in "The Field".
|
.
"The
trackless, uninhabited areas of Western Tasmania, where the serried tops
of high ranges rise like the teeth of some gigantic crosscut saw, and the
intersecting valleys are filled with brown button-grass or densely-matted
rain forest scrub, the remnant of a fast disappearing, primitive animal
manages still to find a living. It is a rather precarious existence,
because the small game on which it feeds is none too common, and sheep,
which, since the first days of white settlement provided it with food,
are far removed from this inhospitable territory in which it has been driven,
to make its last stand".
|
Sydney Morning
Herald, 2nd Feb. 1937 (p. 13),
TASMANIAN TIGER: Marsupial's
Stand, by M. S. R. Sharland
|
.
|
On the night of the 7th September 1936, the last
known captive thylacine died at the Beaumaris Zoo on the Queen's Domain
in Hobart, Tasmania. It has been argued that this was the
"extinction
event", and that this young male represented the last of his kind.
Dr. Bob Paddle, in his book "The Last Tasmanian Tiger", is a proponent
of this position. The alternate viewpoint, championed by the |
| late
Dr.
Eric Guiler (Australia's leading authority on the thylacine), and more
recently by Sleightholme & Campbell (2015), argues that this was not
the case, and provide evidence to support the view that the species survived
well beyond Benjamin's demise.
Extinction is a difficult
event to detect, even in well known taxa such as mammals. The extinction
of an animal species occurs when the last individual member of that species
dies, although the capacity to breed and recover may have been |
.
| A
reclining thylacine at the Beaumaris Zoo (SB). This photo was taken
sometime between 1917 and 1921, by Miss D. O. Park. |
|
|
| lost long before this point. Species
become extinct when they are no longer able to survive in changing conditions,
or against superior competition. A species may become functionally
extinct when only a handful of individuals survive, which are unable to
reproduce due to sparse distribution over a large range, or a lack of individuals
of both sexes. Although a species may be deemed "extinct in the
wild", the species is not extinct until every individual, regardless
of location, captivity, or ability to breed, has died. Because a
species's potential range may be very large, determining the date of extinction
is generally undertaken retrospectively. |
.
| The
"Red List of Threatened Species", published by the International Union
for the Conservation of Nature (IUCN), classified the thylacine as being
extinct in 1986 (McKnight 1986). Prior to 1995, the IUCN deemed a
species to be extinct if it had not been seen or recorded in the past fifty
years. This precept has now changed, with the focus shifting from
that of time lapse to exhaustive survey:
"A taxon is extinct
when there is no reasonable doubt that the last individual has died.
A taxon is presumed extinct when exhaustive surveys in known and / or expected
habitat, at appropriate times (diurnal, seasonal, annual), and throughout
its historic range have failed to record an individual. Surveys should
be over a time frame appropriate to the taxon's life cycle and life form".
By comparison, the IUCN
definition of critically endangered is:
"A category containing
those species that possess an extremely high risk of extinction as a result
of rapid population declines of 80 to more than 90 percent over the previous
10 years (or three generations), a current population size of fewer than
50 individuals, or other factors".
We shall now examine
the factors that contributed to the thylacine's decline and explore the
evidence to countenance the view that the thylacine became extinct in 1936.
In Tasmania,
the thylacine was protected by the natural barrier of the Bass Strait from
the competitive forces that decimated its former range on the Australian
mainland. These competitive forces have been linked with competition
from the placental dingo (Canis lupus dingo), climatic change, and
disease.
Guiler estimated that
the total thylacine population at the time of British settlement (1803)
as being around 2000-4000 individuals. Guiler (1998, p. 138) states:
"Some parts of Tasmania
did not support many, if any thylacines. The rain forests and sagelands,
which account for almost half the surface area of the State, were not favoured
tiger habitat. If this area is subtracted from the total area of
the State, then the average home range of tigers in Tasmania would be reduced
by about one half. The Woolnorth estimates suggest a home range per
individual or pair of between 50 and 60 square kilometres, which would
indicate a Tasmania wide thylacine population between 1357 and 1138 individuals,
or double these two figures (between 2714 and 2276) if each home range
sheltered a pair of tigers. Home ranges of less than 25 square kilometres
would not have provided sufficient space for adequate food, shelter, breeding
dens and other elements necessary to thylacine survival. Therefore,
the conclusion is made that there were between 2000 and 4000 thylacines
living in Tasmania in any one year, and would have been less rather than
more".
All
parties on either side of the extinction / survival debate now agree that
a significant collapse in thylacine numbers occurred during the first decade
of the twentieth century. Sleightholme & Campbell (2015) cite
several factors as being responsible or contributing to this demise: |
.
| -
The bounty schemes |
-
Wild animal trade |
| - Disease |
- Hunting
and the fur trade |
| - Habitat
destruction |
- Trade
in thylacines for museums |
| - Feral
dogs |
|
An examination of each
of these factors to assess its potential effect on thylacine numbers is
therefore warranted. |
