Re: Exctinctions...?

On Sat, 13 Jun 2009 21:31:17 +0100, Ernest Major
<{$to$}@meden.demon.co.uk> wrote:

In message <nJSYl.50442$2t7.11559@xxxxxxxxxxxxx>, Spence...
<"Spence..."@garctec.co.uk> writes
Hi folks,

Sorry if this is a bit OT, but I'm looking for something that will explain
to me the maths of small breeding populations as a cause of extinction... I
saw it on a TV program once... Even though there is breeding, there won;t be
any chance of species survival... Anyone know what i mean..?

Ta.

People talk about species with sufficiently small populations are being
the living dead - extinction being inevitable. While small populations,
especially newly small populations, are at greater risk of extenctionI
have my doubts about the inevitability

For example not only was there a conservation program to save the
Mauritius Kestrel, but it seems to have been successful.

And many successful colonisations by species have involved small
populations - the Cattle Egret jumped the Atlantic (apparently under its
own steam) in the 19th century (first observed in the Guianas in 1877)
and has since spread widely in the Americas (though I can't be sure that
repeated colonisations haven't occurred subsequently). Australia and New
Zealand were colonised in the mid-20th century.

http://www.allaboutbirds.org/guide/Cattle_Egret/lifehistory
http://en.wikipedia.org/wiki/Cattle_Egret

And for many years the domesticated populations of golden hamsters were
descended from a single litter.

http://en.wikipedia.org/wiki/Golden_hamster


An awful lot of alien species now widespread started as very small
populations of colonizers. Earthworms, dandelions, and even that icon
of the American west, the tumbleweed, were introduced into the New
Workd by human colonizers. One person brough a batch of gypsy moth
eggs to America to see if they could be used as a source of silk. The
moths escaped his care and have since devasted millions of acres of
woodland. The ubiquitous starling was introduced in the Americas by
someone who wanted all the birds mentioned by Shakespeare, supposedly
with an original colony of 100. Then there are the rabbits in
Australia.

The point is not that small populations necessarily go extinct.
Obviously they can thrive and multiply. But how many other colonizing
species never made it? Almost certainly a far, far, larger number. It
is the probability of extinction that increases drastically for small
population size, not the certainty.

.

Relevant Pages

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