(out-crossing) has been substituted by insular auto-
gamy (self-compatability). We might anticipate that
any initial advantage in autogamy at the point
of colonization should be of limited duration in
relation to subsequent lineage development.
Interestingly, 237 species of Canarian endemic
plants (almost half the endemic flora) exhibit fea-
tures (such as unisexual flowers, heteromor-
phic styles or self-incompatibilty) promoting
out-breeding (Francisco-Ortega et al. 2000).
Patterns of dioecy and self-crossing vs. outcross-
ing in island floras currently remain poorly under-
stood. As they became better quantified, such
properties may shed interesting light on the evolu-
tionary assemblages of island floras in terms of
what they reveal about the importance of pollinator
mutualisms (below), and may ultimately help us to
understand why some lineages have radiated on
islands while others are absent or have failed to
radiate (Sakai et al. 1995b; Barrett 1996).
Loss of flower attractiveness
Island plants often display a loss of flower showi-
ness, such that they tend to have small, actinomor-
phic (radially symmetrical), white or green
non-showy flowers with simple bowl-shaped corol-
las, instead of the large, tubular, zygomorphic
(bilaterally symmetrical), bright-coloured flowers
frequently displayed on the continents (Carlquist
1974). This trend, is evidenced in a comparison of
Australian and New Zealand floras, and probably
reflects the generalistic and promiscuous nature of
the island pollinators (Barrett 1996), as well as their
smaller sizes when compared to the continental
pollinators. Inoue and Kawahara (1996) were able
to demonstrate a direct correlation between the
flower size of Campanulaspecies and of their polli-
nators. Flowers were larger on the mainland, where
they were visited by larger pollinators (bumblebees
and megachilid bees) lacking from the islands.
Pollination in the island populations was carried
out by smaller pollen-collecting halictid bees,
which were shown experimentally to be indifferent
to flower size, in contrast to the preference for
larger flowers shown by the nectar-feeding
megachilid and bumblebees on the mainlands.
Anemophily
Some island plants appear to have shifted from
ancestral animal pollination to wind pollination
(anemophily). Examples include Rhetinodendronin
the Juan Fernández islands, PlocamaandPhyllisin
the Canaries, and Coprosma in New Zealand
(Ehrendorfer 1979), and it has been suggested
as a general island trend (see e.g. Carlquist 1974,
Ehrendorfer 1979). Possible benefits include:
(1) gaining independence from impoverished
pollinator services (e.g. Goodwillie 1999;
Traveset 2001), (2) windy conditions favouring
anemophily, and (3) outcrossing fitness benefits
yielded by wind pollination (Barrett 1996).
However, as a definitive analysis of the prevalence
of anemophily has yet to be carried out, it would
be hasty to conclude in favour of these mecha-
nisms. Preliminary data for the incidence of
anemophily in the floras of well-studied archipel-
agos yield values varying from 20% for Hawaii
(Sakaiet al. 1995a,b), to 29% for New Zealand and
34% for the Juan Fernández islands (Ehrendorfer
1979). In contrast, McMullen (1987) stressed the
paucity of wind pollination within the native flora
of the Galápagos. Furthermore, anemophily may
be linked to other important features, such as
woodiness or dioecy, thus not of itself indicating
selective advantage.Parthenogenesis
Reproductive mode may also be tied up with colo-
nization probabilities in certain animal taxa.
According to Hanley et al. (1994), parthenogenetic
(asexually reproducing) lizard species are relatively
common on islands. They suggest that this may be
because of: an enhanced colonization ability; the
opportunity to flourish in a biotically less diverse
environment (in which the relative genetic inflexi-
bility that might be associated with parthenogene-
sis is not too disadvantageous); or the opportunity
to escape from hybridization or competition with
their sexual relatives. Their study examined the
coexistence of parthenogenetic and sexual forms of
the gecko Lepidodactyluson Takapoto atoll in French
Polynesia. The two forms of Lepidodactylus,178 ARRIVAL AND CHANGE