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M. Aleffi, C. Cortini Pedrotti & D. Gafta

Patrons bryogéographiques dans les petites iles autour de la Péninsule
italienne, de Sicile et Sardaigne

Abstract

Aleffi. M., Cortini Pedroni, C. & Gafta, D.: Bryogeographic patterns in the small islands sur-
rounding the ltalian penin sula , Sicily and Sardinia. - Bocconea 16(1): 93-103. 2003.- ISSN
1120-4060.

This study aims to analyse the role played by some physiographic and ecologie variables such
as area, isolation , altitude and substratum type on the bryophyte species richness of 49 small
ltalian islands. Both lloristic similarìty between islands and bryophyte species richness depend
above ali on the island size. The other variables, i.e. the proximity to the closest continent or
major island, the distance between ìslands and the type of substratum, account for only small
differences between the island bryolloras. Unexpectedly, the number of bryophyte species in
these islands is not negatively related to the distance from the continent. Thìs outcome is due
to the confounding effect of island size and age, as well as to the stronger human impact that is
likely to occur in close-to-continent islands. The high slope of the species-area curve indicates
a very scarce bryophyte immigration, even from the closest islands. The low dispersion abìlity
ìs partly related to some life history traits of the xerophilous mosses. The only two endemie
species (Rhynchoslegium s/rongylense and Thamnob1ywn cossyrense) that occur in no more
than five islands were not sutlicient to test whether the isolation from the continent has
favoured the differentiation ofnew species. The outcome ofthe analyses performed rellects the
current bryo-chorological knowledge concerning the small ltalian islands, and thus it is likely
that reports of new species could change some bryogeographic patterns revealed in this study.

Introduction

L'étude des patrons explicatifs de la richesse et de la diversité des organismes vivants
au sein des 'ìles continentales, reliées au continent au cours des temps géologiques, ou des
ìles océaniques, le plus souvent d'origine volcanique, demeure un des thèmes majeurs en
écologie et en biogéographie des populations ou des peuplements (Bionde! 1995; Adsersen
1995).

Les études actuelles de biogéographie insulaire reposent encore le plus souvent sur la
théorie de l'équilibre dynamique développée par MacArthur & Wilson ( 1967). Cette
théorie aborde plus particulièrement !es relations superficie-richesse spécifique, et la dual-
ité entre !es taux d'immigration qui contrebalancent !es processus d'extinction des espèces
dans le cadre de la colonisation de systèmes isolés.