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IVORY-BILLS  LiVE???!  ...

=> THE blog devoted to news and commentary on the most iconic bird in American ornithology, the Ivory-billed Woodpecker (IBWO)... and... sometimes other schtuff.
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Sunday, October 02, 2005

 

-- Population bottlenecks --

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The following post from an "Eric" on another bird forum is of some relevance here:
(I didn't realize either that the Whooping Crane had gotten down to 14 individuals!)

"I just did a literature search on this and found that I was wrong. As of 1938 there were only 14 whooping cranes left, not 40. As of 1997 there were 160 in the original wild migrant population, 100 in captivity and 73 in a reintroduced wild population. This number is higher today. I got these numbers from an article by Glen, Stephan and Braun (Effect of a population bottleneck on whooping crane mitochondrial DNA variation. 1999 Conservation Biology vol 13, #5 1097-1107). By comparing mt DNA sequences from museum specimens to those of extant birds they determined that of 6 haplotypes (analogous to "families") existing pre-bottleneck, only one formerly rare haplotype exists today. In other words most of the genetic diversity that once existed is gone today.

On the brighter side of this the birds are recovering despite being highly inbred. Similar findings of low genetic variation in species that have very small effective population sizes have been reported for desert pupfishes. The best known of these is the Devils Hole pupfish (Cyprinodon diabolis) which lives in a water filled limestone fissure near Death Valley. What is significant about this species is that it has an effective population size of less than 200 (the population varies seasonally) and it generally lives less than 2 years. This last point is important since inbreeding depression is a function of number of generations, not time per se.

Taken together, these results imply that inbreeding depression does not always occur in formerly bottlenecked or chronically small populations. It's really probably a luck of the draw whether or not individuals that make it through the bottleneck harbor really deleterious mutations or not.

Back to the subject at hand, it would seem that there is reason to hope that IBW can make some semblance of a recovery, assuming that a population still exists."

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