Contrasting Forest Trajectories Drive Changes in Bird Functional Traits

Abstract

Aim We investigated how bird functional diversity varies across forest habitat types with distinct successional trajectories, namely (1) natural succession forests, with naturally regenerating forests established on former grasslands; (2) secondary forest remnants resulting from deforestation; and (3) conserved forests. Location Araucaria forests in southern Brazil. Time Period 1991 to 2015. Taxon Birds. Methods We compiled functional trait data for bird communities from 47 sites of Araucaria forests under three distinct successional trajectories. We calculated standardised effect sizes for functional richness (SESFRic) and functional dispersion (SESFDis), and generalised linear models were initially fitted. To account for spatial autocorrelation, we fitted spatial models (spaMM) to assess whether forest habitat type, forest cover, and patch size help explain functional variation in bird assemblages. In addition, we performed canonical correspondence analysis to evaluate differences in trait composition among forest habitat types. Results Functional richness and dispersion decreased with increasing forest cover. However, only functional dispersion differed among forest habitat types, indicating environmental filtering across all habitats. Forest cover was the main predictor of functional richness, suggesting that habitat amount limits bird species coexistence. Natural succession forests had lower functional dispersion when compared with secondary forest remnants and conserved forests. Although conserved forest and secondary forest remnants had partially similar responses in functional dispersion, we found significant differences in community trait composition and functional space. Natural succession forests supported insectivorous species that forage in air in addition to species with broader bills, while secondary forest remnants held birds that feed on insects and fruits on ground strata. Conserved forests sustained birds with vertebrate consumption and that forage in leaf litter. Main Conclusions Our results indicate that different forest habitats are shaped by distinct assembly processes: colonizing species during forest expansion in natural succession forests and as a species refuge in secondary forest remnants due to deforestation. Therefore, assessing the landscape features of each forest habitat can help to elucidate the relationship between landscape context and functional diversity, as well as how successional stages influence the dynamics of community assembly.

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