From: steinly@topaz.ucsc.edu (Steinn Sigurdsson)
Newsgroups: sci.environment
Subject: Re: Temperate zone habitat loss
Date: 22 Jan 93 23:55:31 GMT
	<STEINLY.93Jan20124040@topaz.ucsc.edu>
	<1993Jan21.032938.28382@watson.ibm.com>
Organization: Lick Observatory/UCO
NNTP-Posting-Host: topaz.ucsc.edu
In-reply-to: andrewt@watson.ibm.com's message of 21 Jan 93 03:29:38 GMT

In article <1993Jan21.032938.28382@watson.ibm.com> andrewt@watson.ibm.com (Andrew Taylor) writes:

   In article <STEINLY.93Jan20124040@topaz.ucsc.edu> steinly@topaz.ucsc.edu (Steinn Sigurdsson) writes:
   >Same question applies to the issue of birds in North America, does
   >the introduction of say "pet" tropical birds to the US (or turkeys to
   >Europe) make up in any sense for the species lost or restricted and if
   >not, why not? (I know some of the arguments for why those species
   >should be counted with reduced weight but am interested to hear what
   >others think).

   11 accidentally or deliberately introduced foreign species of birds have
   established viable breeding populations in North America north of Mexico.
   Quite a few more foreign species are currently breeding in very small numbers
   but the populations are either considered not viable or the introduction
   occurred too recently to tell.  3 of the 11 species have very restricted ranges.

More than I realised. You're a very good source of information.

   Most of these 11 species are common in their native habitat. As far as I can
   determine all are secure in the native habitat.  Hence these 11 populations
   have no conservation value.  2 of the 11 species are seriously detrimental
   to some native bird species.

   3 of the 11 are game species and were introduced for hunting.  3 of the 11
   are pest species causing large amounts of damage.  I don't have figures for
   the cost of this damage but it must far exceed the economic value of the
   game species.

   So, on balance, the introduced species are both detrimental economically
   and ecologically.  What do you think is positive about these introductions?

Well, we seemed to be concerned about long term speciation potential
at one point. Specifically, the discussion at one point revolved
around the issue that extinction rates must be comparable to
speciation rates (on a long enough time scale) to maintain diversity.
Now, speciation is not well understood. The problem is partially one
of classification, a "new" species is typically assumed to be an old
newly discovered species, or a new sub-species (eg I don't think any
biologist will ever concede that dogs have formed distinct species,
no matter how diverse the sub-species get) - in this context note that
the estimates of species numbers and lifetimes require 1-10 new
species to form per year on average. So, question is whether
establishing a species in a new habitat which they could not reach
naturally will, in the long run, lead to (several) new species 
evolving?
And, should any anthropic contribution to the speciation rate
by habitat fragmentation or by introducing old species to new ranges
where they might diverge from the parent population, count in
balance against anthropic extinction? 

*  Steinn Sigurdsson   			Lick Observatory      	*
*  steinly@lick.ucsc.edu		"standard disclaimer"  	*
*  I know people whose idea of fun				*
*  Is throwing stones in the river in the afternoon sun		*
*  Oh let me be as free as them					*
*  				- BB 1986			*
 
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