●Recent colonization.Where a comparatively
recent colonization event has taken place, landfall
may have occurred on any of the extant islands, such
that some taxa first colonize a young island, with
subsequent dispersal from younger to older islands,
while others may colonize an intermediate-aged
island, subsequently dispersing to both younger and
older islands. This pattern seems to be followed by
Tetramolopium (Asteraceae) and Geranium
(Geraniaceae) in the Hawaiian flora. The blue tit
(Parus caeruleus teneriffaegroup) provides a Canarian
example, with mitochondrial DNA data indicating
first colonization on Tenerife and subsequent spread
both to older and younger islands (Kvist et al. 2005).
●Extinction.If a taxon is specific to habitats such
as high summits, found only on young islands,
then the loss of such habitats from older islands
may result in extinction from all but the youngest
islands. This pattern can be distinguished from
recent colonization in cases where the molecular
clock age estimate indicates a much longer period
of lineage development than could be provided by
the islands on which the taxon currently occurs. In
Hawaii this pattern is exemplified by Clermontia
(Campanulaceae),Geranium(Geraniaceae), and
Argyroxiphium(Asteraceae) plant genera.
●Unresolved.Some cladograms fail to provide a
clear scenario either because of the inherent com-
plexity of the evolutionary sequences involved or
through lack of sufficient data.
●Repeated colonization from outside the
archipelago.This pattern would not be expected in
such a remote situation as Hawaii (although see
Terminal resolution, above), but appears common in
the Canaries (just 60 km from Africa during low sea-
level stands). Repeat colonization produces para-
phyly (separate clades) within a taxonomic group:
for example, at least three different colonization
events have been detected in Calathusbeetles and
Tarentolageckos, and two in the plant genera Ilex
(Aquifoliaceae),Hedera(Araliaceae), and Lavatera
(Malvaceae) (Juan et al. 2000, Emerson 2002).
However, within the flora, the greatest degree of
radiation occurs in genera that appear to be mono-
phyletic (debated in Herben et al. 2005; Saunders
and Gibson 2005; Silvertown et al. 2005).
●Fusion of palaeoislands.A repeated phylogeo-
graphic pattern found within Tenerife, is the
occurrence of allopatric sister taxa in the Anaga
(north-east) and Teno (north-west) peninsulas.
These areas were separate islands until the con-
struction of the Las Cañadas massif during the
Pleistocene fused them together into a single, much
larger island (Chapter 2). Gallotializards, Chalcides
skinks,Pimelia,Calathus, and Eutrichopusbeetles,
Steganecarusmites,Dysderaspiders, and Loboptera
cockroaches among animals (Juan et al. 2000) and
Aeonium,Cheirolophus,Limonium,Lotus,Sideritis,
andTelineamong plant genera (Báezet al. 2001),
have present-day distributions related to this histor-
ical sequence. For instance, Pimeliabeetles show
lineages associated with the west and the east of
Tenerife, which have spread over the central regions
during the Quaternary (Juan et al. 2000).Island-hopping on the grand scale
As will already have become evident, molecular
phylogenetics now allows biogeographers to
reconstruct sequences of movement on the grand
scale, across entire ocean basins. We have already
given examples of how the Canaries have received
colonists not only from Africa, the nearest conti-
nental landmass, but also from Europe via the
Azores and Madeira, from the Cape Verde islands
to the south, and even from America. In short, the
Canaries have received colonists from all points of
the compass, and have also supplied back-colonists
to the African mainland.
The Indian Ocean also provides examples of
complex scenarios of island-hopping. For example,
coastal lizards of the genus Cyrptoblepharusappear
to have colonized the western Indian Ocean
islands by transoceanic dispersal from Australia or
Indonesia. The genus appears then to have diversi-
fied in Madagascar from where it separately colo-
nized the East African coast, the Comoro islands
(twice) and Mauritius (Rocha et al. 2006). Galley
and Linder (2006), in their review of the affinities of
the southern African Cape flora, find that in addi-
tion to some ancient disjunctions across the Indian
Ocean, there is also strong evidence for some very
recent disjunctions, which can only be explained byFROM VALLEY ISOLATES TO ISLAND-HOPPING RADIATIONS 237