5. Adaptive Radiation
77
in Lammers 1990). Average corolla length is slightly (but significantly) shorter on
Kaua'i (37 ± 14 mm) than on the progressively younger islands of O'ahu (54 ± 17
mm), Maui (50± 17 mm), and Hawai'i (51 ± 20 mm). Flower length is probably
related to the bill length of the honeycreeper(s) and other birds that pollinated each
species; interspecific variation in flower length should thus be a measure of the
breadth of the pollinator guild partitioned by Cyanea taxa on each island. This
pattern - combined with a detailed infrageneric analysis that inferred rapid evolutionary increases and decreases in floral length among closely related species -
suggests that Cyanea underwent convergent radiations in flower length on each
major island after a relatively small number of inter-island dispersal events (Givnish
et al. 1995). Most of the inferred inter-island dispersal events were from one island
to the nearest, younger island in the chain (Fig. 4), as would be expected given
constraints on dispersal and the greater likelihood of successful establishment and
subsequent radiation by colonists on nearby, newly formed, ecologically unsaturated islands. Such patterns of inter-island dispersal were first documented in Drosophila (Carson 1983) based on chromosomal banding patterns, and have now been
reported for many other Hawaiian groups, including the silversword alliance (Carr
et al. 1989; Baldwin 1992), Alsininidendron-Schiedea (Wagner et al. 1995; Sakai
5,1
3.7
26
1.9
1.3 0.8
0.4 My.
r----r----r-L--+----r~--fl'--~'-rl----~I'
o
100
200
300
400
500
600
o~
Kaua'j
~ , O'ahu
(17)
~5)
2
\
~ ","'N,;
'0-\)~26)
II
700 km
Fig. 4. Minimum number of inter-island dispersal events needed to account for present-day
species in Cyanea, based on molecular and morphological data (after Givnish et al. 1995);
note tendency for species to disperse from one island to the next younger one. Width of each
arrow is proportional to the number of dispersal events between the corresponding pair of
islands; the number of species found on each island or island group is indicated in parentheses. Mya, million years ago
77
in Lammers 1990). Average corolla length is slightly (but significantly) shorter on
Kaua'i (37 ± 14 mm) than on the progressively younger islands of O'ahu (54 ± 17
mm), Maui (50± 17 mm), and Hawai'i (51 ± 20 mm). Flower length is probably
related to the bill length of the honeycreeper(s) and other birds that pollinated each
species; interspecific variation in flower length should thus be a measure of the
breadth of the pollinator guild partitioned by Cyanea taxa on each island. This
pattern - combined with a detailed infrageneric analysis that inferred rapid evolutionary increases and decreases in floral length among closely related species -
suggests that Cyanea underwent convergent radiations in flower length on each
major island after a relatively small number of inter-island dispersal events (Givnish
et al. 1995). Most of the inferred inter-island dispersal events were from one island
to the nearest, younger island in the chain (Fig. 4), as would be expected given
constraints on dispersal and the greater likelihood of successful establishment and
subsequent radiation by colonists on nearby, newly formed, ecologically unsaturated islands. Such patterns of inter-island dispersal were first documented in Drosophila (Carson 1983) based on chromosomal banding patterns, and have now been
reported for many other Hawaiian groups, including the silversword alliance (Carr
et al. 1989; Baldwin 1992), Alsininidendron-Schiedea (Wagner et al. 1995; Sakai
5,1
3.7
26
1.9
1.3 0.8
0.4 My.
r----r----r-L--+----r~--fl'--~'-rl----~I'
o
100
200
300
400
500
600
o~
Kaua'j
~ , O'ahu
(17)
~5)
2
\
~ ","'N,;
'0-\)~26)
II
700 km
Fig. 4. Minimum number of inter-island dispersal events needed to account for present-day
species in Cyanea, based on molecular and morphological data (after Givnish et al. 1995);
note tendency for species to disperse from one island to the next younger one. Width of each
arrow is proportional to the number of dispersal events between the corresponding pair of
islands; the number of species found on each island or island group is indicated in parentheses. Mya, million years ago