0198566123.pdf

ADAPTIVE RADIATION 221

Scratch

for seeds

on the

ground

Feed on

seeds on the

ground and

the flowers and

pulp of Prickly

Pear(Opuntia)

Feed in trees

on beetles

use spines held

in the bill to

extract insects

from bark

crevices

Feed on leaves,

buds, and seeds

in the canopy of

trees

Warbler-like birds

feeding on small

soft insects

Ce. olicacea

Ce. fusca

P. crassirostris

C. pauper

G. fortis

G. fuliginosa14 g

20 g

34 g

21 g

28 g

18 g

21 g

34 g

13 g

10 g

(b)

8 g

20 g

20 g

13 g

G. magnirostris

G. scandens

G. conirostris

G. difficilis

C. parvulus

C. psittacula

C. pallida

Pi. inornata

Figure 9.5(b) Darwin’s finches, the Emberizinae, are endemic to these islands. There are a number of different phylogenetic hypotheses of how
these taxa relate to each other. The genetic distance between each species is shown by the length of the horizontal lines. The maximum amount
of black colouring in the male plumage and the average body mass are shown for each species. This version is taken from Townsendet al. (2003)
after Petren et al. (1999).

A comprehensive theory for this radiation was
developed by Lack (1947a) and has been updated
and summarized by Grant (1981, 1984; and see
Vincek et al. 1997). The key points are as follows.
One of the Galápagos islands was colonized from
the mainland in a one-off founding event. Genetic
analyses suggest that the effective population size of

the founding flock was at least 30 individuals

(Vincek et al. 1997). The founding population

expanded quite rapidly, undergoing selective

changes and/or drift. After some time, members of

this population colonized another island in the

archipelago, where conditions were slightly different.

Further changes occurred through a combination of