BIOGEOGRAPHY OF THE PELAGIAN ISLANDS
Lampedusa and Linosa are very different islands, one is calcareous, the other volcanic; therefore it is understandable that the fauna is also different. However, most of the species present on these two islands have either migrated to them or, in the case of Lampedusa, they represent a proof of an ancient connection with Tunisia.
One point on which each and everyone agree upon is the fact that the Pelagian islands, compared to other Mediterranean islands, hosts the least number of species. This owes its main explanation to their distance from the mainland. Linosa, located 163 km from the nearest coast, is certainly the most isolated of the two; its small size, combined with this remarkable isolation, although dampened by the presence of other islands (the Maltese archipelago to the East, Lampedusa to the South-West and Pantelleria to the North-West) with the possibility of stepping stones (lands of gradual colonization), as well to the poor environmental heterogeneity, justify its faunal poverty. Lampedusa, in comparison with Linosa, although having a modest surface and altitude, is proportionally richer in species; this can be mainly explained by its calcareous nature, which seems to offer more opportunities for settlement to many species of Arthropods. However, due consideration must be given to the position of Lampedusa, which offers a coastal front of 11 km in the East-West direction (well above the 3.5 of Linosa) between the two continents of Europe and Africa, thus having greater statistical opportunities to "attract" towards itself any active and passive propagules (individuals who actively or passively move for the propagation of the species), especially those facilitated by the northerly and south winds; and, of course, also its geological history, marked by a continuous land connectivity with North Africa at least during the last glacial period; this, in particular, seems to be witnessed by the conspicuous presence of species with little or no ability to colonize ( for example some Tenebrionidae Beetles) of clear African origin or which show notable affinity with elements distributed in the Maghreb. Finally, the altitude of both islands is rather modest, especially if compared to that of another nearby island in the Sicilian Channel, Pantelleria.
The relationship between Arthropods and their host plants appears to be of some interest; the presence of phytophagous species closely associated with species of alien plants, imported in recent historical times on the islands, is certainly proof of the rapid immigration of insects. Climate and vegetation changes must have had a different impact on the living species, causing multiple extinctions of species and at the same time allowing new ones to migrate to a more suited current climate situation. This particularly highlights the problem of the representativeness of the faunal observations made today. Moreover, the current fauna and flora populations seem rather recent and, at least where Vertebrates are concerned, which seems that these were not present before the last glaciation. Only in Lampedusa remains of an extinct fossil mammalian fauna, relatively recent and of a clear North African origin, have been discovered. The bathymetry between the island and Tunisia makes it possible to hypothesize this wildlife migration at the moment of maximum lowering of the sea level, coinciding with the glacial peak of the Würm (18,000 years ago). Certainly part of the current fauna present on Lampedusa, although minimal, is a relic of periods preceding the last glaciation, but most species must have immigrated there in more recent times.
In spite of being about one million years old, Linosa has been subjected to great climatic, physical and vegetational changes, which occurred up to a few thousand years ago, and it is therefore likely that it has received faunistic (and floristic) populations starting from its emergence, but without the communities present before the last glaciation have reached completely (or even partially) to the present day. Extinctions and immigrations have therefore repeatedly modified the composition of zoocoenoses (together with faunistic communities).