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(canonical R2 = 0.56) and percentage of land cover gave Distances to the nearest island and to the mainland were
not identified as of any statistical importance in affecting
F2 = 20.85, P = 0.47 (canonical R2 = 0.52). Thus, in species numbers. This suggests that, in general, species
(21) richness on the circum-Sicilian islands is not regulated by
“stepping stone” processes or “mainland-island” dyna-
both cases, there was no significant correlation between mics (for an example within the sub-system of the Aeo-
lian Islands, see Fattorini, 2010). This is probably a
biogeographical patterns and land cover. consequence of two characteristics of the study system.
First, the circum-Sicilian islands are a composite assem-
DISCUSSION blage of islands and “stepping stone” processes or
“mainland-island” dynamics may be important for some
The species-area relationship is the most widespread islands (Fattorini, 2010) but not for others. Second, tene-
and best documented pattern in macroecology (cf. brionids are, in general, sedentary animals and their
Rosenzweig, 1995). For the tenebrionids of the circum- occurrence on islands is typically better explained by
Sicilian islands, island area accounted for most of the relict models (i.e., by colonization via land-bridge con-
variability in species numbers, as previously observed for nections followed by local extinction after disconnection)
other Mediterranean islands (e.g. Fattorini, 2002a, 2009a, than equilibrial ones (i.e., by current overseas dispersal)
2009b, c). Their species richness increased with various (Fattorini, 2002b, 2006a, 2007). Although geographical
measures of environmental diversity and decreased with distances did not exert a clear influence on species rich-
environmental homogeneity. This accords with the fact ness, they are important in determining species composi-
that landscape diversity typically increases the diversity tion. In particular, distance to Sicily exerted an important
of generalist insects (Jonsen & Fahrig, 1997; Krauss et influence in determining species composition on Pan-
al., 2003). telleria and the Pelagie Islands, which are among the
remotest islands, whereas the distance to Africa was of
Relationship between species richness and environ- less importance. These results suggest that colonization of
mental diversity in island biogeography is typically inves- all islands occurred mainly from Sicily and the process
tigated within the wider framework of the species-habitat depended on the dispersal ability of each species. Lomo-
diversity hypothesis (see Hortal et al., 2009). However, lino (2000) stressed the importance of differences in the
this may be incorrect as the term “habitat” is often mis- colonization ability of individual species to explain distri-
used. For example, previous studies using “number of butional patterns in island systems. The importance of
habitats” used, in reality, number of biotopes; see Dennis sources and the observation that the impoverishment of
(2010) for a distinction between habitat and biotope. A island faunas is influenced by species characteristics was
recent model by Kadmon & Allouche (2007) found spe- recently demonstrated for butterflies on the Tyrrhenian
cies richness to follow a uni-modal distribution in relation islands (Dapporto & Dennis, 2008a, 2009). In this
to increasing biotope numbers (“habitat diversity” respect, species assemblages on highly isolated islands
according to their use): species diversity initially should be strongly affected by isolation, which selects the
increases with number of biotopes from a very simple most “successful” colonizers from the species pool in the
island towards biotope-wise more complex islands, until a source areas.
maximum species richness is reached, and then it declines
because too many biotope types imply that the total areas Island area was particularly important in regulating spe-
of individual biotope types are small, reducing the area of cies assemblages on the Maltese islands. This small archi-
suitable biotopes for any given species. In contrast, Hortal pelago includes the largest islands and is also very iso-
et al. (2009) found that species richness on islands usually lated. Thus, it is a well defined sub-system and the largest
increases with the number of biotopes and never island, Malta, may act as a source of species for its
decreases. Results obtained for the tenebrionids on the smaller, satellite islands.
circum-Sicilian islands support the findings of Hortal et
al. (2009) not only for the number of biotopes but also for The circum-Sicilian islands are biogeographically
various measures of environmental diversity. strongly structured, as revealed by cluster analysis and
multidimensional scaling. Both techniques show that
In the last few decades, there has been a continuous faunal similarities among islands reflect their geo-
debate on whether area per se or “habitat” diversity is graphical and paleogeographical relationships. CAN-
more important in influencing species richness on islands. CORs revealed a strong influence of distance and sea
Some studies support the idea that the species-area rela- depth to Africa. Thus, although species assemblages on
tionship derives from the fact that larger islands have a islands are not influenced by relationships with Africa,
greater “habitat diversity” (Báldi, 2008; Jonsson et al., this is an important factor for inter-island similarity. In
2009), others indicate that there is a strong effect of area particular, position of the Maltese Islands and Lampedusa
per se (Nilsson et al., 1988; Marini et al., 2010) and many along the first dimension of multidimensional scaling,
report a mixed effect (Ricklefs & Lovette, 1999; Kal- related to current and past isolation from Africa, fits with
limanis et al., 2008). For the tenebrionids of the circum- the paleogeographical history of these islands. Relation-
Sicilian islands, correlations between residuals from the ships of Lampedusa with the African mainland are also
species-area relationship and measures of landscape het- testified by the occurrence of African elements, such as
erogeneity suggest that some of the variation in species
richness not explained by area can be attributed to land-
scape heterogeneity. Thus, both area and landscape diver-
sity may contribute to species richness.
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