Evolution__3rd_Edition

504 PART 4 / Evolution and Diversity
(a) Fruitflies
Kauai
(12)
(b) Tarweeds
Kauai
(13)
N
1
2
5
2
200 km
125 miles
1
Oahu
(29)
Oahu
(4)
2
10
Mediterranean-type ecosystems
have evolved convergently
Biogeographic evidence supports
evolution
1
2
7
3
Maui
complex
(40)
15
Maui
complex
(12)
6
1
Hawaii
(26)
Hawaii
(7)
Figure 17.6
The dispersal events suggested by the phylogeny of the Hawaiian
picture-wing group of fruitflies (Drosophila). The phylogeny is
shown in Figure 15.27 (p. 465), but the numbers used here are not
exactly those implied by the previous diagram because this figure
is more recent. The numbers in the arrows are the inferred
number of dispersal events; parenthetic numbers by the island
names are the number of endemic species living on that island.
(b) A comparable figure for the tarweed plant. The geological
history of the archipelago, in which the islands have been
successively formed toward the east, has imposed the same
biogeographic histories on the two groups. Redrawn, by
permission of the publisher, from Carr et al. (1989).
The similarity of the plants in the five Mediterranean regions is due to convergent
evolution. The shrubs of the Mediterranean itself are unrelated to the shrubs of
California or Chile. The plants in the European Mediterranean are related to other
European species; they have evolved from local ancestors. It is not the case that a
Mediterranean set of species have evolved once and spread to all five regions.
The Mediterranean ecosystems illustrate a general point that Darwin discussed in
On the Origin of Species (1859), and used as evidence for evolution. The species within
any large geographic area tend to be more closely related to each other than to ecologically
more similar species elsewhere in the globe. In Australia and South America
(particularly before the Great American Interchange, which we shall look at below
in Section 17.9), the main mammals have been marsupials. Both marsupials and eutherian
mammal groups have evolved a saber-toothed “tiger,” for example (Figure 15.4,
p. 429), but the eutherian is a real cat (in the taxonomic sense) whereas the South
American equivalent was a marsupial. The pattern makes sense, Darwin argued, if
species evolved from other species in the same general area. That is, new mammal
species in Australia were more often descended from other Australian mammals than
from, say, North American mammals. If a species such as the saber-toothed tiger had
been specially created, we might expect it to be much the same everywhere. There is
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