Descrizione
Descrizione
EFFETTI DELL'INSULARITÀ SULLA RICCHEZZA E STRUTTURA DELLE COMUNITÀ ORNITICHE IN UN AMBIENTE MEDITERRANEO
STEFANO GELLINI, PIERANDREA BRICHETTI PIERPAOLO CECCARELLI e UGO F. FOSCHI
Riassunto - Il confronto delle comunità di ambiente di macchia e di pineta del promontorio del Gargano e delle Isole Tremiti evidenzia un rilevante effetto di impoverimento faunistico sulle isole e la presenza di un effetto di compensazione di densità relativamente all'Occhiocotto Sylvia melanocephala in ambiente di pineta.
Abstract - Consequences of insularity on the richness and structure of the bird communities in a mediterranean environment. The birds of the Gargano promontory and of the Tremiti Islands (Southern Italy) have been censused in two habitats: maquis and pine-woods of Pinus halepensis. Censuses were taken using the IPA technique. Remarkable effects of faunistic impoverishment have been recorded on islands. We have calculated the expected number of species accepting the hypotesis that the island counts are drawn randomly from the Promontory counts. We have thus obtained a loss of 14 species in the pine-woods and of 5 species in the maquis. A t the species level, Sylvia mefanocephala shows a phenomenon of density compensation in the pine-woods on the islands (probably due to the absence of Svlvia atricapilla) but not in the maquis. Carduelis carduelis (the only species, along with Sylvia mefanocephala, common both to the islands and to the Promontory) does not show any effect of compensation, despite the absence or rarity of Fringilla coelebs, Carduelis ehlori.,· and Serinus serinus. Carduelis carduelis is a recent colonizer, an d perhaps is stili numerically below the environment carrying capacity.