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Alfred Russel Wallace on passenger pigeons (was RE: Theories on t he extinction of dinosaurs)

I've recently had the pleasure of reading a number of Alfred Russel
Wallace's papers (thanks to a cheap CD ROM _greatest works_ collection): &
found this bitterly ironic passage in ON THE TENDENCY OF VARIETIES TO DEPART
INDEFINITELY FROM THE ORIGINAL TYPE (written by Wallace at Ternate, February
1858). Hard to tell whether there is any direct insight on the extinction of
the dinosaurs in Wallace's particularly unfortunate example; but it seems to
me worth repeating.

Once we got at them seriously, the poor creatures barely lasted 50 years....

All the best,
Robert Clements <Robert.Clements@dva.gov.au>


This is strikingly proved by the case of particular species; for we find
that their abundance in individuals bears no relation whatever to their
fertility in producing offspring. Perhaps the most remarkable instance of an
immense bird population is that of the passenger pigeon of the United
States, which lays only one, or at most two eggs, and is said to rear
generally but one young one. Why is this bird so extraordinarily abundant,
while others producing two or three times as many young are much less
plentiful? The explanation is not difficult. The food most congenial to this
species, and on which it thrives best, is abundantly distributed over a very
extensive region, offering such difference of soil and climate, that in one
part or another of the area the supply never fails. The bird is capable of a
very rapid and long-continued flight, so that it can pass without fatigue
over the whole of the district it inhabits, and as soon as the supply of
food begins to fail in one place is able to discover a fresh feeding-ground.
This example strikingly shows us that the procuring a constant supply of
wholesome food is almost the sole condition requisite for ensuring the rapid
increase of a given species, since neither the limited fecundity, nor the
unrestrained attacks of birds of prey and of man are here sufficient to
check it.