Fire disturbance disrupts co-occurrence patterns of terrestrial vertebrates in Mediterranean woodlands

Abstract

This paper uses null model analysis to explore the pattern of species co-occurrence of terrestrial vertebrate fauna in fire-prone, mixed evergreen oak woodlands. Location: The Erico-Quercion ilicis of the Mediterranean belt (50-800 m a.s.l.) in the Madonie mountain range, a regional park in northern Sicily (37°50′ N, 14°05′ E), Italy. Methods: The stratified sampling of vertebrates in a secondary succession of recent burned areas (BA, 1-2 years old), intermediate burned areas (INT, 4-10 years old) and ancient burned areas (CNB, > 50 years old), plus forest fragments left within burned areas (FF, 1-2 years old) permitted the comparison of patterns of species co-occurrence using a set of separate presence/absence matrices. First, the breeding avifauna derived from standardized point counts was analysed using Stone & Roberts'C-score, and by a null model algorithm (fixed/equiprobable). Secondly, the analysis was repeated using all vertebrate species recorded in the succession. Results: Sixty-five species were recorded in the 2-year study period in the four sample treatments. Birds were found to make up the largest component (63%) of the recorded assemblage. The BA treatment had the lowest species richness, followed in order by the small, medium and large FFs, and then by the CNBs. For both analyses (birds and total vertebrates), the C-scores were quite small and not significantly different from those that could be expected by chance in the BA and INT burned areas; this indicates a random co-occurrence among vertebrates of those assemblages. Contrariwise, for both analyses in the CNBs, the C-scores were large and significantly different from the simulated indices, thereby indicating a non-random co-occurrence pattern (segregation) of vertebrates in the undisturbed woodlands. In addition, C-score values for the surviving FFs show a significant aggregation of species. Main conclusions: The null model analyses highlighted a new aspect of fire disturbance in Mediterranean woodland ecosystems: the disruption in patterns of co-occurrence in the terrestrial vertebrate community. Wildfire alters community organization, inducing, for at least 10 years, a random aggregate of species. Communities re-assemble themselves, showing the occurrence of species segregation at least 50 years after fire. © 2006 Blackwell Publishing Ltd.