Late Pleistocene landscape changes and habitat specialization as promoters of population genomic divergence in Amazonian floodplain birds.

Although vicariant processes are expected to leave similar genomic signatures among codistributed taxa, ecological traits such as habitat and stratum can influence genetic divergence within species. Here, we combined landscape history and habitat specialization to understand the historical and ecological factors responsible for current levels of genetic divergence in three species of birds specialized in seasonally flooded habitats in muddy rivers and which are widespread in the Amazon basin but have isolated populations in the Rio Branco. Populations of the white-bellied spinetail (Mazaria propinqua), lesser wagtail-tyrant (Stigmatura napensis) and bicolored conebill (Conirostrum bicolor) are currently isolated in the Rio Branco by the black-waters of the lower Rio Negro, offering a unique opportunity to test the effect of river colour as a barrier to gene flow. We used ultraconserved elements (UCEs) to test alternative hypotheses of population history in a comparative phylogeographical approach by modelling genetic structure, demographic history and testing for shared divergence time among codistributed taxa. Our analyses revealed that (i) all three populations from the Rio Branco floodplains are genetically distinct from other populations along the Amazon River floodplains; (ii) these divergences are the result of at least two distinct events, consistent with species habitat specialization; and (iii) the most likely model of population evolution includes lower population connectivity during the Late Pleistocene transition (~250,000 years ago), with gene flow being completely disrupted after the Last Glacial Maximum (~21,000 years ago). Our findings highlight how landscape evolution modulates population connectivity in habitat specialist species and how organisms can have different responses to the same historical processes of environmental change, depending on their habitat affinity.

The role of physical barriers in the location of avian suture zones in the Guiana Shield, northern Amazonia.

Suture zones represent natural forums in which to examine the role of geography and ecology in the speciation process. Here, we conduct a comparative analysis designed to investigate the location of avian phylogeographic breaks and contact zones in the Guiana Shield, northern Amazonia. We use distributional and genetic data from 78 pairs of avian taxa to address whether phylogeographic breaks and contact zones are associated with contemporary landscape features. Using spatially explicit statistical models, we found that phylogeographic breaks and contact zones are not randomly distributed throughout the landscape. In general, geographic breaks cluster along physical barriers (rivers, nonforested habitats, and small mountain ranges), whereas contact zones aggregate where these barriers either break down or are easier to overcome, such as around rivers' headwaters. Our results indicate that although major Amazonian rivers are often key determinants of taxon boundaries, the "riverine barrier effect" is a synergistic consequence of the wide lower reaches of some rivers, coupled with nonriverine landscape features at the headwaters. Our data suggest that ancestral refugia are not necessary to explain current distribution patterns and that pairs of codistributed taxa do not seem to be the result of simultaneous diversification processes.

Abundance of two Dendrocincla woodcreepers (aves: Dendrocolaptidae) in relation to forest structure in Central Amazonia / O uso do habitat por duas espécies de arapaçus Dendrocincla (aves: Dendrocolaptidae) em relação a estrutura da floresta na Amazônia Central

Few studies have been conducted to verify how the structure of the forest affects the occurence and abundance of neotropical birds. Our research was undertaken between January 2002 and July 2004 at the Reserva Ducke, near Manaus (02°55',03°01'S; 59°53',59°59'W) in central Amazonia, to verify how the forest structure affects the occurrence and abundance of two bird species: the Plain-brown Woodcreeper Dendrocincla fuliginosa and the White-chinned Woodcreeper Dendrocincla merula. Bird species occurrence was recorded using lines of 20 mist-nets (one sample unit), along 51 1-km transects distributed along 9 pararel 8 km trails covering an area of 6400 ha. Along these transects, we placed 50 x 50m plots where we recorded forest structure components (tree abundance, canopy openness, leaf litter, standing dead trees, logs, proximity to streams, and altitude). We then related these variables to bird occurence and abundance using multiple logistic and multiple linear regression models, respectively. We found that D. fuliginosa frequently used plateau areas; being more abundant in areas with more trees. On the other hand, D. merula occurred more frequently and was more abundant in areas with low tree abundance. Our results suggest that although both species overlap in the reserve (both were recorded in at least 68 percent of the sampled sites), they differ in the way they use the forest microhabitats. Therefore, local variation in the forest structure may contribute to the coexistence of congeneric species and may help to maintain local alpha diversity.

Em florestas neotropicais, poucos estudos tem sido conduzidos para verificar como a estrutura da floresta afeta o uso desse ambiente por aves. Este estudo foi realizado entre Janeiro de 2002 e Julho de 2004 na Reserva Ducke próximo a Manaus (02°55',03°01'S; 59°53',59°59'W), para verificar como a estrutura da floresta afeta a ocorrência e abundância de duas espécies de aves: o Arapaçu-pardo, Dendrocincla fuliginosa e o Arapaçu-da-taoca, Dendrocincla merula. A ocorrência das espécies de aves foi registrada com 20 redes ornitológicas (unidade amostral), dispostas em linha contínua ao longo de cada um dos 51 transectos de 1 km distribuídos ao longo de nove trilhas pararelas de 8 km em uma área de 6400 ha. Em cada transecto foram demarcadas parcelas de 50 x 50 m, para registrar alguns componentes da estrutura da floresta (abundância de árvores, abertura do dossel, folhiço, troncos mortos em pé, troncos mortos no chão, proximidade de igarapés e altitude) os quais foram então relacionados com a ocorrência e a abundância das aves através de modelos de regressão múltipla logística e múltipla linear, respectivamente. D.fuliginosa utiliza mais frequentemente áreas de platô, e a sua abundância foi maior em áreas com maior abundância de árvores. D.merula ocorreu mais freqüentemente e em maiores abundâncias em áreas com baixa abundância de árvores. Os resultados sugerem que as duas espécies sobrepõem suas áreas de uso (ambas foram registradas em pelo menos 68,6 por cento dos locais amostrados), mas elas separaram-se no modo de uso do microhabitat. Portanto, a variação local na estrutura da floresta pode contribuir para a co-ocorrência de espécies congenéricas e deve ajudar a manter a diversidade alfa local.