Evolution__3rd_Edition

500 PART 4 / Evolution and Diversity
Figure 17.4
(a) Distribution of the main
genetic clades of hedgehogs
(Erinaceus species) in Europe.
They are currently classified
into two species, but the two
probably hybridize.
(a)
Spanish
clade
German
clade
Italian
clade
Balkan
clade
these remarkable fish have diverged into a number of (perhaps four) species, and when
the next pluvial period brings water to the desert, they may expand from their interpluvial
refuges to encounter one another in a process that is analogous to the expansion
of European hedgehogs after the last ice age.
17.5 Local adaptive radiations occur on island archipelagos
Adaptive radiation means that an ancestral species evolves into a number of descendant
species, each with distinct ecological adaptations. A single speciation event often occurs
as two species, with different ecological adaptations, evolve from a single ancestral
species (Section 14.3, p. 383). A local adaptive radiation occurs when several such speciation
events occur in a local area. As we shall see in Chapter 23, adaptive radiation can
be studied on a global scale, if the adaptive radiation of a taxon persists for a long
enough time. But here we shall be looking at smaller scale adaptive radiations a those
that are only a slight extension of the speciation process we looked at in Chapter 14.
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