>Finch beaks are an interesting case, but not very instructive because the
>process cannot be observed, so we can only imagine what must be
>responsible. This would be a poor substitute for the Peppered moths.
Art, I ran into this several years ago and it seems to fit the bill (no pun
intended) of the requirement of observation.
"The i'iwi (Vestiaria coccinea) is a Hawaiian honeyeater which, as records
from the last century show, used to feed largely by extracting nectar from
lobelioid flowers. The i'iwi's long, downcurved bill is well adapted for
extracting the nectar from the base of the deep corollas of these flowers,
which they pollinate in the process. But lobelioids are no longer
abundant, and in a paper in Conservation Biology Smith and colleagues
describe evidence that the i'iwi's bill is evolving in response to the
bird's enforced change in feeding habits.
"Lobelioids used to be a prominent component of Hawaiian forests. In the
past 100 years, however, a quarter of the species have become extinct and
the remainder are rare as a result of habitat changes and grazing by feral
ungulates. I'iwi now feed largely upon the flowers of the ohia treee,
Mestrosideros polymorpha. According to nineteenth-century naturalists,
i'iwis were excluded from this tree by the aggressive behaviour of another
honeyeater, th 'o'o (Moho nobilis). But the 'o'o was extinct by 1900.
"Ohia flowers lack corollas and the other honeyeater species that feed
upon them have short bills. Smit et al. thus predicted that the i'iwi
should evolve a shorter bill and they compared measurements of museum
specimens collected before 1902 with measurements of live specimens. This
analysis showed that i'iwis have undergone statistically significant
declines in upper mandible length by about 2-3 percent, whereas characters
such as wing or tarsus length are the same. No such change in mandible
length was recorded in a related honeyeater species, the aparine Himatione
sanguinea, that had not altered its diet.
"The classic example of a microevolutionary change in bill morphology is
that in one of Darwin's finches, Geospiza fortis, on Daphne Major Island in
the Galapagos. There the population shows rapid declines in bill depth and
width after severe El Nino events, as a result of a short-term fall in the
abundance of large seeds and an increase in small ones. The especial
interest in the case of the i'iwi, however, is that the adaptations in bill
length are a response to extinctions and are likely to be
long-lived."~William J. Sutherland, "I'iwis fit the Bill," Nature May 4,
1995, 375, p. 14.
glenn
Adam, Apes and Anthropology
Foundation, Fall and Flood
& lots of creation/evolution information
http://www.isource.net/~grmorton/dmd.htm