Disentangling patch and landscape constraints of nested assemblages

Abstract

The role of the matrix for the functionality of residual patches and therefore for species persistence has been recently recognised. However its influence on assemblage structure and composition is still unclear. We studied the effect of both patch and matrix attributes on community assemblage structure and composition in a fragmented landscape of central Italy. We used bird assemblages as a study model. Birds were sampled in 24 wood patches and distribution patterns were analysed considering both assemblage and guild-level responses. Patch composition and structure together with landscape patterns quantified with GIS were used as explanatory variables. The assemblages appeared to be strongly influenced by the landscape context, both in terms of composition and configuration. The functional connectivity of the patches, in terms of amount of neighbouring borders between woods and hedgerows, the shape of the woods in the matrix, together with the age of the patches, expressed as tree diameter, acted as the essential determinants, and even if the assemblages presented a significant nested structure, seven out of 40 species showed an idiosyncratic distribution. The study of the association between functional guilds and environmental parameters highlighted the influence of ecological constraints on the occurrence of unexpected presences and absences, suggesting the ability of some species to perceive and exploit matrix habitats. The matrix holds the capability to at least mitigate the effects of isolation and habitat loss, and the semi-natural elements of the mosaic may represent a biodiversity reservoir in an otherwise deprived landscape.