Breeding Avifauna of a Mediterranean Succession: The Holm oak and Cork Oak Series in the Eastern Pyrenees, 1. Analysis and Modelling of the Structure Gradient

Abstract

Within the Mediterranean level of the Alberes chain, 186 samples were taken in different formations from grassland to forest, with presence-absence sampling of the bird and plant species, and estimation of the relative cover of 7 vegetation layers, plus the rock itself. After multidimensional ordination (Correspondence Analysis) of the birds x stations matrix, and multiple correlation of the first factor F1 of C.A. with the 8 cover values, a model results which, (1) proves that F. is the expression of a progressive evolution of the vegetation structure, (2) shows that there is a logarithmic relationship between this structural evolution and bird species turnover, (3) permits a calculation, for any station of the studied region, of optimal indices of avifaunistic gradient and of structure gradient, (4) allows one to predict semi-quantitatively, from the vegetation structure, the probable avifauna of any station, and vice versa. This gradient analysis is a good alternative to the classical model (unidimensional sequence of discrete classes), especially when an ecological succession is reconstructed from the simultaneous comparison of different stations.