Pericallis,Cheirolophus,Argyranthemum, and Sonchus;
and there are almost equally impressive radiations
within the genera Echium(Boraginaceae),Lotus
(Fabaceae),Sideritis(Lamiaceae), and Limonium
(Plumbaginaceae) (Sziemer 2000; Izquierdo et al.
2004).
Smaller oceanic islands, even in the tropics (e.g.
the Cook Islands), have much smaller floras and
typically lower proportions of endemics. This is due
in part to the reduced variety of habitats and to the
wide mixing of the typically sea-dispersed strand-
line species that dominate their floras. Another fea-
ture of the data which must be borne in mind when
examining statistics for island endemism is that in
some areas there are numerous species which are
endemic to islands, but which are shared between
different geographical entities. Thus, in the Lesser
Antilles (the Leeward and Windward Islands), the
shared or regional island endemics form a consider-
able proportion of the endemic flora as a whole.
Endemic animals
The following constitutes a selection of some of the
animal groups that are sufficiently well-known to
be placed into either a regional or global context
with some degree of confidence.
Land snails
There may be as many as 30 000–35 000 land snail
species in the world (Groombridge 1992), of which
a substantial proportion occur on islands (Wallace
1902). Some of the better-known of island snail
faunas are quantified in Table 3.3. Although only
eight archipelagos are listed in the table, they
account for approximately 7.7–9.0% of the world’s
land snails by present estimates (some regions of
the world remain poorly known and the current
picture could change) (Groombridge 1992). Studies
in the Pacific suggest that, once again, it is the
larger, higher oceanic islands (15–40 km^2 , >400 m
ASL) that typically have both most species and most
endemics, whereas low-lying atolls have neither
high richness nor high degrees of endemism. On
most islands with high snail diversity, the snails
appear to be concentrated in the interiors, espe-
cially mountainous regions with ‘primary’ forest
cover. For those islands with good data, a marked
positive correlation exists between numbers of
endemic plant species and endemic molluscs, but
not between molluscs and birds (Groombridge
1992).Insects
No attempt will be made to cover the insects in a
systematic fashion, but the following statistics
from Hawaii and the Canaries give an idea. In the
family Drosophilidae (fruit flies), 511 species are
currently named and described for Hawaii, with
another 250–300 awaiting description (Wagner and
Funk 1995). Given the pattern of discovery, it is
estimated that there may be as many as 1000
endemic species. The radiation of tree crickets on
the archipelago has resulted in 3 endemic genera
and some 68 species. The orthotyline plant bug
genusSaronais another endemic Hawaiian genus,
with 40 known species. Moving across to the
Atlantic Ocean, the Canarian insect fauna is
increasingly well studied, and comprises some
5700 species and 500 subspecies, of which almost
2200 species and 370 subspecies are considered
endemic (Izquierdo et al. 2004). Among them,
perhaps the most explosive example of radiation is
offered by the weevil genus Laparocerus, compris-
ing some 65 monophyletic species, with approxi-
mately another 40 waiting to be described and
may be as many more waiting to be discovered
(Antonio Machado, personal communication).ENDEMISM 67Table 3.3 Land snail species richness and endemism for selected
islands for which the data are complete enough for the proportion of
endemics to be estimated (from Groombridge 1992, Table 14.3)Island or Number of Number of % Endemic
archipelago species endemic
speciesHawaiian Islands c.1000 c.1000 99.9
Japan 492 487 99
Madagascar 380 361 95
New Caledonia 300 c.299 99
Madeira 237 171 88
Canary Islands 181 141 77.9
Mascarene Islands 145 127 87.6
Rapa 105 105 100?