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Boll. Soc. Entomol. 136/3 29-11-2004 17:56 Pagina 240

240 LO CASCIO & ROMANO

Jaccard’s coefficients (see Figure 2). Tuscan (TUS) and Egadi (EGA) archipelagos were
considered as single insular entities, because of the low species richness on each of their
islands and of the homogeneous species composition of the islands making up each ar-
chipelago. In order to obtain groups of islands/areas with a certain degree of internal
homogeneity, an average linkage cluster analysis (UPGMA) was used (Sneath & Sokal,
1973). The clustering was carried out using MVSP package (version 3.1); the resulting
dendrogram is reported in Figure 2. The clusters show the occurrence of two main groups,
the “Sardinian” and the “Tyrrhenian-Sicilian”, from which both Lampedusa appears to
be clearly isolated. This result was easily predictable due to the geographical position
of this island, geologically belonging to the Tunisian platform. In the cluster analysis,
a comparison between Lampedusa and North Africa was not attempted because of the
incomplete faunal knowledge of the latter. Concerning the “Tyrrhenian-Sicilian” group,
the highest similarity (0.55) proved to be that between Tuscan Islands and Uccellina
Mounts. The latter area, located in Southern Tuscany, may be regarded as a sub-fossil
island of the Tuscan Pleistocene archipelago, whose fauna was recently investigated (Lo
Cascio et al., 1998). This group includes also the circumsicilian Lipari and Egadi Is-
lands, which proved to be more related to Tuscan and Uccellina than to the nearest Sicily.
These “peri-tyrrhenian” areas show a high zoogeographical homogeneity, which is more
likely to depend on factors that could influence the composition of their faunas, such
as similar climate and vegetation (see Pignatti, 1994), than to their relative geographi-
cal nearness. The other clearly recognisable group, the “Sardinian” one, pertains to a
distinct cluster principally because of the high number of endemics occurring on its is-
lands. Furthermore, the circumsardinian islands show a greater similarity to each other
than to the main island; this is probably due to certain ecological selectivity in the fau-
nal composition of micro-insular environments.

The chorological compositions of different island groups (fig. 3-8) show a decrease
of “european” (EUR, SEU) and “widely distributed” (EUM, SIE), and an increase of
the “mediterranean” (MED, WME, NAF, END) elements along a North-South latitudi-
nal gradient. As already stated, endemics (END) are present mainly on circumsardinian
islands, where they reach 33% in the northern islands and 32% in the southern ones (fig.
4 and 5). A “continental” mark distinguishes the chorological compositions of both Tus-
can and Aeolian archipelagos (fig. 3 and 6), characterised by the prevalence of “european”
and “widely distributed” chorotypes. In a zoogeographical perspective, it is interesting
to note that, unlike what happens in other groups of arthropods, the Corsican-Sardin-
ian endemic Mutillid wasps do not occur on Tuscan Islands. However, further
investigations on some islands so far unsufficiently known (e.g. Capraia and Montecristo)
are needed to confirm this apparent absence. Finally, the North-African chorotype ap-
pears exclusively in the chorological spectra of the circumsicilian Egadi and particularly
of Lampedusa (fig. 7 and 8), the southernmost among all the considered islands, where
it is present in a percentage of 27.5%.

Most taxa occur only on one or few islands, but few species, such as Ronisia bru-
tia and R. ghilianii, show a widespread presence in micro-insular environments (see fig.
9). R. brutia was recorded for several Central- and East-Mediterranean minor islands:
Maltese, Dalmatian, Ionian, Cyclades, and Dodecanese (Invrea, 1941; 1942; 1954; 1964;