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tion at the boundary between Europe and Africa makes
their faunal composition a mosaic of European and
African elements (Fattorini, 2010, 2011) with important
conservation implications (Fattorini, 2008b).

Thanks to their low dispersal ability, tenebrionids are
excellent biogeographical markers of historical processes
(Fattorini, 2001b, 2008a, 2009a, c). They have been
repeatedly used to investigate the biogeography of Medi-
terranean islands (e.g. Fattorini 2002a, 2006a, b, 2009a, c,
2010, 2011; Hausdorf & Hennig, 2005). The distribution
of tenebrionid beetles on the circum-Sicilian islands is
well known, yet there is no comprehensive biogeog-
raphical study. In this paper, the tenebrionid beetles on
the circum-Sicilian islands are used to explore how the
same geographical and environmental factors influence
species richness, species composition of communities and
variation in the similarity of communities.

MATERIAL AND METHODS Fig. 1. Map of the study area with sea depths (a). Island posi-
tions within archipelagos are detailed for the Aeolian (b), Egadi
Study islands (c) and Maltese Islands (d). Islands names are as follows: 1 –
Lipari, 2 – Salina, 3 – Vulcano, 4 – Stromboli, 5 – Filicudi, 6 –
The circum-Sicilian islands (Fig. 1) can be grouped into four Alicudi, 7 – Panarea, 8 – Basiluzzo, 9 – Lisca Bianca, 10 – Bot-
main archipelagos: the Aeolian Islands (volcanic), the Egadi taro, 11 – Scoglio Faraglione, 12 – Pietra del Bagno, 13 –
Islands (sedimentary), the Pelagie Islands (both volcanic and Ustica, 14 – Levanzo, 15 – Favignana, 16 – Marettimo, 17 –
sedimentary) and the Maltese Islands (sedimentary); the Pantelleria, 18 – Linosa, 19 – Lampione, 20 – Lampedusa, 21 –
remaining two islands, Ustica and Pantelleria (both volcanic), Malta, 22 – Gozo, 23 – Comino, 24 – Cominotto, 25 – Filfla.
are rather isolated. The Aeolian Islands are separated from
Sicily by a sea channel of about 1000–2000 m depth and thus used sea depths among islands and between islands and the
they have always remained apart from Sicily, even during Pleis- mainland (Crowell, 1986).
tocene falls in sea level. The sea between the islands (except
between Vulcano and Lipari) is also very deep (about 400–1400 To characterize environmental conditions, I calculated the
m) and prevented Pleistocene inter-island connections. All the extent of island surface occupied by different land cover catego-
Egadi islands are calcareous and at least two islands, Favignana ries according to the European Corine Land Cover classifi-
and Levanzo, were repeatedly connected to Sicily either in the cation. Although somewhat crude, Corine land cover categories
Lower and Middle Pleistocene (Calabrian and Ionian stages) are extensively used to express species-environment relation-
between 1.8 million and 126,000 years ago or in the Upper ships (e.g., Lobo & Martín-Piera, 2002; Stefanescu et al., 2004;
Pleistocene (Tarantian stage) during the Würm glaciation about Maes et al., 2005). A total of 24 land cover categories were
18,000 years ago. The island of Ustica is separated from Sicily found on the circum-Sicilian islands. This is too many predic-
by a deep and wide sea channel and has always remained apart tors compared to the small number of islands composing the
from Sicily, even during Pleistocene falls in sea level. Lampe- archipelago. Moreover, some categories were represented by
dusa and Lampione are an emerged portion of the African conti- very small patches or can be easily combined into broader cate-
nental shelf, and were connected to North Africa during the gories. Thus, I constructed the following main categories of
Würm glaciation. Pantelleria and Linosa were not connected to landscape types (Table 2): Built up areas (including Continuous
mainland areas (Sicily or North Africa). Finally, the Maltese
Islands were connected to Sicily and probably to North Africa
during the Pleistocene, but their separation from Africa occurred
long before that from Sicily. For detailed information on these
islands see Corti (1973), Mazzola et al. (2001) and The Maltese
Islands Multimedia Encyclopedia (2011).

Measurements of geographical and environmental variables

The geographical parameters are summarized in Table 1.
Both island area and isolation are important factors regulating
species occurrences on islands (Whittaker, 1998). As measures
of island isolation, I considered here both island distance to
Sicily or North Africa (both considered as the closest
“mainland” areas) and to the nearest island (Table 1); see Fatto-
rini (2010) for details.

Sea level changed greatly during the Pleistocene, determining
both inter-island and island-mainland connections. As a rule,
falls in sea level connected areas above a depth of 200–150 m. It
can be assumed that, during Pleistocene falls in sea level, lower
depths permitted longer connections with wider land bridges
between islands and/or to the mainland. Thus, to study the influ-
ence of paleogeography on species richness and composition, I

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