have favoured the same mutations, resulting in two
related taxa of separate (i.e. paraphyletic) origin
being incorrectly classified as one species.
The first scenario is considered by far the most
frequent (e.g. Funk and Wagner 1995).
Examples of parallel microevolution have been
documented within Canarian Nesotesbeetles. On
morphological criteria, N. fusculuswas considered
a MIE, occupying the xeric coastal zones of Gran
Canaria, La Gomera and Tenerife. However, phy-
logenetic analysis showed this ‘species’ to be para-
phyletic, with the ‘fusculus’ phenotype having
evolved independently on each of the three
islands (Rees et al. 2001). A similar scenario applies
toN. conformis, a laurel forest dweller, found on
Gran Canaria, Tenerife, La Palma, and El Hierro.
Phylogenetic analyses revealed that the laurel
forest phenotype evolved twice within Gran
Canaria and once more on the western Canaries
(Emerson 2002). This last example appears to
show that paraphylly can pertain even for an
apparent SIE.
Just over half (57%) of the endemic Canarian
flora (bryophytes vascular plant species) are
SIEs, with two thirds of these species being found
either on Tenerife or on Gran Canaria (Table 9.5).
Nevertheless, each island also harbours more MIEs
than SIE species. For instance, Tenerife harbours
151 MIEs and 107 SIEs and Gran Canaria harbours
100 MIEs and 75 SIEs. Intriguingly, the number of
endemic species found on two or more islands
does not decline smoothly with increasing number
of islands as might be expected, with some 45
species being shared by the five high islands of
Gran Canaria, Tenerife, La Palma, La Gomera, and
El Hierro (Table 9.5). This pattern is repeated for
animals, of which 57.5% (1679 species) are SIEs and
42.5% (1239 species) are MIEs. Tenerife (644
species) and Gran Canaria (351 species) again
account for the majority of SIEs (data from
Izquierdo et al. 2001).
How proportions of SIEs and MIEs vary bet-
ween taxa and archipelagos remains to be estab-
lished. We provide a preliminary compilation of
floristic data for three further volcanic archipela-
gos: the Azores (Borges et al. 2005), the Cape Verde
islands (Arechavaleta et al. 2005) and the Galápagos
(Lawesson et al. 1987) (Table 9.6). As in the
Canaries, the SIEs of the Cape Verde and Galápagos
are the largest single category, but they account for
only 22% of endemics, in contrast to 57% SIEs in
the Canarian endemic flora. In the Azorean flora,
the commonest pattern is of MIEs found on all nine
islands, again constituting 22% of endemics. These
simple analyses serve to show that the proportions
of SIEs and MIEs vary considerably between archi-
pelagos. We can only speculate as to the reasons for
these differences. It may be that the Canaries are in
some respects more effectively isolated from one232 EMERGENT MODELS OF ISLAND EVOLUTION
Table 9.5Distribution patterns amongst the endemic plant species of the Canaries (Source: Izquierdo et al. 2001, reworked)
Islands occupied 1 2 3 4 5 6 7 Total
Species no. 289 75 44 30 45 9 19 511
% 56.6 14.7 8.6 5.9 8.8 1.8 3.7 100
More frequent distributions in T 107 TC 18 PGT 9 PGTC 8 HPGTC 42 HPGTCF 5
order of importance
C 75 PT 17 GTC 8 HPGT 7 GTCFL 2 PGTCFL 3
P 36 FL 17 HPT 5 HGTC 7
G 35 GT 11 HPG 5 TCFL 3
H 13 HP 4 CFL 5 HPTC 2
F 11 PG 3 HGT 4
L 12 HG 2T, Tenerife; C, Gran Canaria; P, La Palma; G, La Gomera; H, El Hierro; F, Fuerteventura; L, Lanzarote.