However, the Canaries also provide examples
where phylogeographical analysis has shown a pat-
tern of colonization not predictable by distance to
the nearest continent and in opposition to the pro-
gression rule. For instance, finches of the genus
Fringilla(chaffinches), originally from the Iberian
peninsular, colonized the western Canaries via the
Azores and Madeira (Marshall and Baker 1999),
whilePericallis(Asteraceae) may have colonized
the Canaries from America (Panero et al. 1999).
●Intraisland radiation.Within-island radiation
following colonization by an ancestral species has
already been discussed at length, and may involve
both adaptive radiation and non-adaptive radia-
tion. The latter may be related to periods of intrais-
land isolation and the complex geological and
environmental history of an island. Hawaiian
examples of intraisland radiation include Geranium,
silverswords (ArgyroxiphiumandWilkesia), and
Platydesma(Rutaceae). This pattern is frequently
found as part of a larger archipelagic radiation.
●Stochastic.Apparent stochasticity in distribution
in relation to the developmental history of the
archipelago may result from high vagility (as seems
to be the case for the Hawaiian honeycreepers
(Drepanidinae) in so far as we can understand their
now fragmented distribution), or from a recent
establishment on the archipelago, colonizing adja-
cent islands in a random fashion (e.g. Tetramolopium,
in the Asteraceae).
●Back-dispersal.This refers to lieages that gener-
ally may follow the progression rule, but in which
one or more cases of dispersal from a younger to an
older island occur, with subsequent speciation occur-
ring from the back-dispersed colonist. This phenom-
enon can only be detected with certainty by
molecular analysis. Examples include Progna-
thogrylluscrickets, and Kokia(Malvaceae) on Hawaii
(Funk and Wagner 1995) and Pimeliabeetles in the
Canaries (Juan et al. 2000). Recent studies have
demonstrated that the back-dispersal pattern can
even reach the continent from which the ancestral
species of the lineage originated. Examples of plant
lineages back-colonizing Africa from the Canaries
include species in the genera Sonchus(S. bourgaeui,S.
pinnatifidus),Aeonium(A. arboreum,A. korneliuslemsii)
(Santos-Guerra 1999) and Convolvulus(C. fernandesii)
(Carineet al. 2004).FROM VALLEY ISOLATES TO ISLAND-HOPPING RADIATIONS 235Table 9.7 Biogeographical-evolutionary patterns exhibited by selected Hawaiian (Funk and Wagner 1995) and
Macaronesian taxa (sources given in text). Some taxa provide examples of several patterns
Pattern typology Hawaiian taxa Macaronesian taxa
Progression rule Drosophila,Hesperomannia, Olea,Gallotia,Hegeter,Gonopteryx
Hibiscadelphus,Kokia,Remya,
Tetragnatha
Radiation Clermontia,Cyanea,Geranium, Echium,Limonium,Pericallis
Prognathogryllus,Platydesma
Stochastic Drepanidinae,Scaveola, Echium, Crassulaceae
Back-dispersal Clermontia,Geranium,Kokia, Pimelia
Laupala,Sarona
Progressive clades and grades Drosophila,Laupala,Dubautia
Terminal resolution Cyanea,Drosophila,Sarona
Recent colonization Tetramolopium,Clermontia Parus caeruleus
Extinction Clermontia,Geranium,Argyroxyphium
Repeated colonization Unlikely to have occurred Calathus,Tarentola,Ilex,Lavatera,
Hedera
Fusion of palaeo-islands Gallotia,Steganecaurus, Pimelia,
Eutrichopus,Dysdera
Unresolved Clermontia,Sarona Chalcides