Influência do habitat na seleção de grupos filogenéticos e atributos funcionais de aves em florestas ribeirinhas amazônicas do Rio Branco

Abstract

Riverine forests, locally known as varzeas, represent the second main habitat in terms of area of the Amazon basin. The varzeas are directly influenced by the seasonal flooding caused by raise of the level of the rivers, and reveal a series of different riverine habitats which have specific avifaunas and are directly influenced by a flooding gradient. In the rio Branco basin, these habitats include the rivers themselves, as well as beaches, sandbars, riverine florests, flooded and transitional forests. On the upper rio Branco, flooded forests are replaced by gallery forests. The main goal of this study was to describe the association between those different habitats and the avifauna, and understand how these animal assemblages are functionally and phylogenetically structured. Specifically, I aimed to i) describe patterns of species richness across different riverine habitats; ii) describe how the structural complexity of habitats found along a flooding gradient determines patterns of functional and phylogenetic diversity; iii) compare and relate different diversity metrics (species richness, and functional and phylogenetic diversity); and iv) identify which functional traits are selected by the different habitats. To reach these goals, we conducted three expeditions into the rio Branco from 2012 to 2014. Where we conducted systematic avian surveys across the entire length of the river. Overall, we detected 315 bird species during our surveys, and these were used for all the analyses. To define the list of bird species that occur in each habitat, we complemented the result of our surveys with mist-nets and specimen collections. These specimens were used to obtain morphological measurements related to different functional traits of each species, including measurements of mass, bill length, height, and width, lenght of the tarsus, tail, and nail, and the kipp index, a measurement of flying capacity. To describe phylogenetic diversity, I used data from Jetz et al. (2012) to built a tree with all the 315 species. Our results showed that forest habitats presented higher species richness than relatively simpler habitats, such as rivers, beaches and sand banks.However, bird assemblages associated to rivers and beaches presented higher levels of functional and phylogenetic diversity, showing no correlation between species richness and other diversity metrics. Some functional traits were clearly associated to different habitats; for ex., larger birds with longer bills and tarsi were clearly associated to rivers and beaches, likely related to the life style of aquatic birds and shorebirds. On the other hand, taller and wider bills, typical of granivorous birds, dominated sandbar scrubs. Smaller birds with shorter bills and tarsi were associated to forested environments. This study shows that habitats affect bird species composition, filtering morphologic traits and selecting which species can leave in each habitat. In general, we found a high degree of species especialization, given that 1/3 of the species were exc;usive of certain habitats. This habitat especificity turns riverine birds vulnerable to changes in river hydrology, and changes in riverine habitats due to human interventions can affect dramaticaly the avifauna of the varzeas.