5 Journal of Mediterranean Ecology vol. 4, No.2, 2003 Journal of Mediterranean Ecology vol. 4, No.2, 2003: 5-21 © Firma Effe Publisher, Reggio Emilia, I Introduction Spatial diversity patterns (Whittaker, 1977; Begon et al., 1986), including latitude and altitude related patterns of species richness, are of particular interest in biogeo- graphy (e.g. Fischer, 1959; Schall & Pianka, 1978; Ro- senzweig, 1992). The factors determining these patterns are complex and differ according to the scale of analysis, the context and the taxa investigated (Kathleen Lyons & Willig, 1999; Cotgreave & Harvey, 1994; Blackburn & Gaston, 1996). In the peninsular patterns there is a generally trend of progressive reduction in species richness, along the pe- Patterns of landbird species composition in Italy: A chorological approach focusing on trends and contra-trends along the peninsula Corrado Battisti (*), Anna Testi (**) (*) Provincia di Roma – Servizio Pianificazione ambientale, sviluppo parchi, riserve naturali - Via Tiburtina 691, I – 00159 Rome, Italy. (cbattisti@inwind.it) (**) Orto Botanico di Roma, Dipartimento di Biologia delle Piante – Università degli Studi di Roma “La Sapienza”, L.go Cristina di Svezia 24, I – 00165 Rome, Italy. (anna.testi@uniroma1.it) Keywords: Chorology, Italy, landbirds, peninsula effect. Abstract The aim of this study was to analyse chorological patterns of breeding landbirds to find ecogeographical factors responsible for trends, contra-trends and discontinuities along the Italian peninsula. The study was conducted in continental (northern) and penin- sular (central-southern) Italy. Italy was subdivided into 27 latitude bands from North to South. For each band, the proportions among the breeding landbird species belonging to different chorotypes was calculated and correlated with the latitude, the maxi- mum altitude and the area of Mediterranean climate. The Cluster Analysis and the Correspondence Analysis performed on the chorotypes matrix showed a clear subdivision into two groups, i.e. the two main Italian bioclimatic regions (Eurosiberian and Mediterranean). Along the Italian peninsula, the proportion of northern chorotypes (Holarctic, Eurasiatic, Eurosiberian, Eurocen- tral-asiatic, European) was positively correlated with latitude and maximum altitude, and negatively with the area of Mediterra- nean climate. The southern chorotypes (Eastern-Palearctic, Olopalearctic, Eurocentralasiatic-Mediterranean, Euroturanic-Medi- terranean, Mediterranean) behave in specular fashion. The European species represent the intermediate chorotype between the northern group and the southern one. The two main chorological groups divide Italy into two sectors: One continental, north of the bioclimatic boundary between Medi- terranean and Eurosiberian regions, and the other peninsular, to the south. Calabrian subpeninsula is chorologically separate from the rest of the Italian peninsula. Furthermore, areas with large changes in bird community composition emerged both in the Corre- spondence Analysis and in the Diversity Indices: 1) at the level of the bioclimatic boundary; 2) at the Southern tip of the Abruzzo Apennines; and 3) at the border of the Calabrian subpeninsula. ninsulas from mainland to the tip. According to Simpson (1964) this could be interpreted as extinction-recolonisa- tion dynamics (MacArthur & Wilson; 1967): However the shape of peninsulas could influence these processes and consequently the species richness, expecially in the distal portions of peninsulas (peninsula effect according to Taylor & Regal 1978). It was observed that several factors ( e.g. , orogeo- graphic, climatic, anthropic), often interacting together and independent from the “Simpsonian” dynamics could affect the peninsular patterns (Kathleen Lyons & Willig, 1999). Furthermore, these patterns are not universal and a number of exceptions occur: In fact, a progressive in-