Published: Volume 31(1), June 1984. Pages 103-113.
Original Title: La segregación espacial de los túrdidos (Turdidae) en el Sistema Central
This paper investigates the patterns of distribution by seven genera of chats and thrushes (Turdidae) along the elevational gradient (700-2.400 m.a.s.l.) of the Sistema Central mountains (Spain). The breeding birds in the eleven most extensive habitats (Table I) were censused by the frequential sampling method in 747 plots, yielding relative estimates of abundance and several indices of habitat and structural occupancy over the gradient (Table II). A Factorial Analysis performed on these data demonstrates that segregation of congeneric species in the group is achieved by means both of vegetation structure and altitude (Table III, Fig. 1). A second analysis centred on the evolution of the specific densities along two different continuous altitudinal gradients (forests of Holm oaks, Pyrenean oaks and Scots pines and shrublands of Cistus, Erica and Cytisus, respectively) shows the existence of altitudinal distributions consistent with Terborgh's (1971) model of distributions over gradients determined by physical and biological factors (Fig. 2). These patterns suggest the scarce importance of ecotones and competitive exclusion as determinants of the turdids distributions in these mountains even though both causes have been implicated to operate in other gradients (and in a related American guild). Results are interpreted in the light of the insular nature of these mountains for northern turdid species and of current views on the ecological relevance of competition in seasonal environments.
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