Reply to message below from Roger M.
1. The perceived problems of lack of genetic diverstiy when animals are
kept captive are not merely "perceived" they are very much real and
fairly well-documented.
2. This does not contradict the other statement in your message that
"small populations will have a small genetic diversity whether it is
becoming extinct in the wild or being kept in captivity". The issue of
wild populations becoming too small is a very real problem also and not
merely a perceived one. The scientific community has discussed "minimum
viable population size" at some length, and while there may be difficulty
or disagreement regarding what that size is for a specific population,
there is a fairly widespread consensus that below a certain size,
populations become highly vulnerable to extinction.
3. The very attributes of captive breeding that can make it attractive
as a solution in extreme cases when species are close to extinction, are
the same ones that may introduce genetic problems in captive breeding
situations beyond those in natural populations. In a captive situation,
relatively few parents can give rise to many progeny by artificially
boosting survival in a controlled environment. After several
generations, the genetic diversity of the resulting captive population
will still be limited by the "effective" number of outside adults who
originally contributed their gametes to it. Such "genetic bottlenecks"
do in fact play an important role in natural populations as well and can
contribute to natural population extinctions when populations become too
small. Natural selection and other factors play some role in tempering
their importance in a natural situation compared to an artificial one.
4. Several unique problems can occur when captive raised organisms are
re-introduced into the wild, particularly if the ecosystem/environment
into which they are released is degraded and/or can only support a small
number of organisms. The captive-raised and artificially-selected
organisms can dilute, swamp, or compete with the limited number of wild
organisms.
5. In my view, the proper priorities are, to the greatest extent
possible, (a) protect natural ecosystems and prevent natural populations
from dropping to a point where there viability is threatened, (b) restore
degraded ecosystems and rebuild natural populations, and (c) rely on
captive breeding where (a) and (b) are not practical and it is necessary
to reduce the risk of extinction.
6. When captive breeding is used, techniques that increase the
diversity of the captive population can and should be employed.
Similarly, if organisms are reintroduced, steps can and should be taken,
to restrict the risk posed to local populations.
7. Regarding the "wildness does not necessarily equal perfection"
comment, this is largely a philosophical issue. My own view is that
wildness comes close enough that keeping a portion of our natural world
wild is a very worthy endeavour. However, my conception of wildness may
not agree with that posed by RogerM. which seems to refer to a tiny
remnant of degraded and altered environment that can only support
extremely small remnant populations of organisms that are genetically
threatened due to their small size. This does not apply to naturally
small populations, which are a separate issue.
On April 15th, Roger M. wrote:
>I keep reading about the perceived problems of lack of genetic diversity
>when animals are kept captive. I remember that Cheeta ((spelling?)
African >cats and the fastest land mammals - are so lacking in genetic
diversity that >skin can be grafted from one to another and the body does
not reject it. As >far as I know these are and have been primarily wild
animals rather than >captive pets.
> It seems to me that a small population will have a small diversity
>whether it is becoming extinct in the wild or being kept in captivity.
>Wildness does not necessarily equal perfection.
>Roger