From: dean@vexcel.com (Dean Alaska)
Subject: Re: Temperate zone habitat loss
Organization: VEXCEL Corporation, Boulder CO
Date: Fri, 22 Jan 1993 16:59:26 GMT

In article <149180335@hpindda.cup.hp.com> alanm@hpindda.cup.hp.com (Alan McGowen) writes:
>
>When a population size is small (Ne < 500, or for most species, population
>size < a few thousand) genetic factors can be of enormous importance.
>In that case, loss of immediate factors of fitness (a phenomenon
>called "inbreeding depression") is possible, and loss of *selectable* 
>(not neutral) variation can cause great damage to maintenance of adaptation.

When one considers this in light of projects such as the one to save
the California condor (population = 7?), it seems that the limited
resources available may not be going to the most important and
productive uses.  I once commented on the long term viability of
a population so low - that its potential for future evolution may be
lost.  Someone (was it Andrew?) commented that the first limit a
population reaches (as it decreases) is that which threatens its
survival in the face of rare natural (or anthropogenic, I guess)
disasters.  In other words, the population needed for adequate genetic
diversity was less than that required to survive rare disasters (such
as a major forest conflagration) that spans much of its range.

I think this all emphasizes the need for the the coherent approach
towards such problems that would be more likely with the type of
biology institute that Alan has mentioned.  Crisis management of
biodiversity issues by emotional politics does not seem to match
the priorities that would emerge from a triage approach.
(Surprise, surprise)

>
>For more info, see Michael Soule's (ed) _Conservation Biology: the
>Science of Scarcity and Diversity_ and _Viable Populations for Conservation_
>for more about MVP.
>
>Note that none of the above points about MVP takes into account the ripple
>effect of extinctions in an ecosystems, resulting from connections of 
>organisms via food webs, as competitors, and as mutualists. This is another
>idealized omission of the MVP models, which tacitly assume that extinction 
>probabilities can be calculated independently for populations.  Work in 
>blending this population-oriented approach with community ecology and food 
>webs is an active area today. See Pimm's the _Balance of Nature_ for efforts 
>in this direction.
>
>Major efforts to obtain direct measurements of how extinction rates vary
>with fragment size are now underway [e.g. the Minimum Critical Size of
>Ecosystems project.] The results to date are consistent with the broad 
>predictions of island biogeography theory and with the idea that a roughly
>inverse exponential decay to the new equilibrium is common when area is 
>reduced.
>
>------------
>Alan McGowen
>
>Incidently, for those that care, the above is intended as an example of
>a "constructive post".
>
>
>"Models are tools for thinkers, not crutches for the thoughtless." 
>-- Michael Soule


-- 
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	Dean Myerson     (aka dingo in boulder)     dean@vexcel.com
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Xref: sparky sci.environment:14841 soc.culture.usa:10107