Sucessional trajetories of bird assemblages in amazonian secondary forests: Perspectives from complementary biodiversity dimensions

Abstract

Secondary forests occupy extensive areas in tropical regions, providing an opportunity to investigate their relevance to biodiversity restoration. However, determining the conservation value of secondary forests and evaluating their successional trajectories depends on how biodiversity is measured. Here, we explore different biodiversity dimensions to understand how bird assemblages recover from forest disturbance caused by small scale farmers in the Amazon. We sampled bird species through standard visual and auditory censuses in 24 small plots of 1-hectare distributed in a paired design of old growth forests and secondary forests from different age categories (early, middle and late succession). We used 12 biodiversity metrics to explore the taxonomic, functional, and phylogenetic dimensions of bird diversity. Total species richness and evenness was similar between secondary and old growth forests. In contrast, the number of passerine species and disturbance-vulnerable species were higher in the controls of old growth forests compared to secondary forests. The relative abundance of birds with distinct functional traits consistently differed between the secondary forests of different age categories and their old growth forest counterparts. Functional evenness and divergence increased with canopy height and basal area through forest regeneration. In contrast, bird phylogenetic diversity in secondary forests was higher compared to those found in old growth forests while accounting for forest types and age categories of secondary forests. Bird species tolerant to disturbances partially compensate the loss of avian taxonomic and phylogenetic diversity during the conversion of undisturbed forests to agricultural fields. Changes in functional evenness and functional divergence suggest that resources used by birds are altered along the secondary succession and that the niche complementarity among species is reduced in more intensively managed sites. Ecological succession can be highly complex in terms of taxa identity, their functional roles and evolutionary history. Therefore, measurements that explore distinct biodiversity dimensions are fundamental to understanding how species are organized in assemblages across time and space.