Skipper impoverishment on large West Mediterranean islands (Lepidoptera Hesperioidea): deterministic, historical and stochastic factors

Abstract

Biogeographical analyses are applied to skipper (Hesperioidea) presence/ absence data from the Western Mediterranean mainland and the three largest islands (Sardinia, Corsica and Sicily) in order to identify potential conservation issues. The analyses performed on species, both collectively and individually, indicate that regional species richness and occurrence in the Mediterranean zone are largely predicted by latitude and area but that islands have impoverished faunas. Several species, predicted to be present on these islands from logistic regression of their continental distributions, are actually absent. The number of species predicted to be present from logistic regression analyses for each island, closely matched the number of species predicted to occur in regional-focused multiple regression analysis. This suggests that missing species have been identified. When compared with species that occur in Sicily and Corsica, the missing species are shown to differ for ecological traits, mainly those linked to altitudinal tolerance. No ecological distinctions were disclosed for Sardinian skippers suggesting a mainly stochastic colonisation. These results, and those from an analogous study carried out on Papilionoidea, point to Hesperioidea having (i) overall more impoverished faunas on islands and (ii) being subject to stochastic or historical colonisation events more than Papilionoidea. Species not predicted to occur on islands based on their mainland distributions and ecological traits, are Electronic supplementary material The online version of this article (foci for conservation attention. However, as many species becoming extinct on the islands may be irreplaceable, all species, in particular the Sardinian ones, deserve to be conserved.

Tenebrionid beetle distributional patterns in Italy: multiple colonisation trajectories in a biogeographical crossroad

“…The large numbers of tenebrionid species and the high levels of endemism found in these islands support their role as refugial and speciation centres, as postulated by Prediction 8b. This result strongly contrasts with the island impoverishment found in butterflies (Dapporto & Dennis, , ), but it is consistent with fossil vertebrate data (Masini et al ., ) and demonstrates that large and isolated islands may represent more stable refugia than the neighbouring mainland.…”

“…Biogeographical patterns shown by Italian tenebrionids and their assumed trajectories are very different from those known for other insects such as butterflies and dragonflies. In general, studies on butterflies showed that highest species diversity straddles montane southern central Europe, and declines systematically northwards and southwards throughout peninsular Italy (see Dennis et al ., ; Dennis & Williams, ; Dapporto & Dennis, , ). This pattern is therefore opposite to that of tenebrionids, and cannot be attributed to sampling bias, because faunal data for European butterflies are very robust.…”

“…Prediction 8a : If island faunas are a result of recent colonisation from mainland areas, islands and mainlands should differ in species numbers even after correcting for other factors, such as area and climate, because of a number of effects related to isolation. In particular, islands should have impoverished faunas because only with difficulty can they be colonised by species with reduced dispersal ability (Dapporto & Dennis, , ). Also, island populations should be more subject to extinction, which should further diminish their species richness (Lomolino et al ., ).…”

Spatial distributions of European Tenebrionidae point to multiple postglacial colonization trajectories

“…A striking pattern found in our study is that the tenebrionid faunas of major islands in the Mediterranean were not significantly impoverished. This strongly contrasts with what is known for lepidopterans, which clearly show impoverished faunas on Mediterranean islands, such as Sardinia and Corsica (Dapporto & Dennis, 2009, 2010). Most probably, these islands, not affected by glaciations, have largely retained their tenebrionid Tertiary faunas which, because of the long period of isolation, have evolved large numbers of endemic taxa.…”

Spatial distributions of European clearwing moths (Lepidoptera: Sesiidae)

“…Dapporto & Dennis, 2009). Islands and mainland areas should also differ in species richness and number of endemics, even after correcting for other factors, such as area, heterogeneity, temperature and latitude, as is reported by Dapporto & Dennis (2010).…”