Data from: Effect of two geologically distinct Amazonian rivers in shaping forest understorey bird assemblages

The earliest observations that Amazonian rivers can limit species
distributions were made by Wallace in 1852. Two centuries later, the role
of major rivers as drivers of biogeographic patterns in Amazonia is still
a matter of debate. The effects of rivers as barriers for species
dispersal can be expected to vary according to both species traits (such
as body size and diet) and the characteristics of rivers themselves (such
as flow rate, channel width, geological age, geomorphology, and floodplain
dynamics). For example, the cumulative barrier effect of young rivers
experiencing a dynamic history is expected to be less pronounced than that
of old rivers coursing through stable channels. The evolution of river
basins can therefore have a profound impact on the biogeography of the
surrounding biota. We used data from standardized bird surveys to compare
upland bird assemblages between opposite banks of two contrasting major
Amazonian rivers. The Juruá is a highly meandering river carrying high
sediment loads and draining the Solimões sedimentary basin, whereas the
Tapajós is an entrenched river with low sediment load that runs through
the cratonic area of the ancient Brazilian shield. Our objective was to
investigate dissimilarities in species composition across each river and
relate them to each river's characteristics and history. We found
significant differences in bird assemblages between the opposite margins
of the stable Tapajós, but not the more dynamic Juruá. This supports the
notion that rivers experiencing a more dynamic history exert a weaker
geographic barrier effect, and that geomorphological setting and landscape
history are important determinants of the effect of Amazonian rivers on
the dispersal and diversification of Amazonian vertebrate taxa.