Connecting Amazonian historical biogeography and local assemblages of understorey birds: recurrent guild proportionality within areas of endemism.

Aim: Current diversity patterns in local communities result from
historical and contemporary events that operate at distinct spatial and
temporal scales. ​However, the contribution of local and large-scale
processes in structuring species diversity remain a contentious topic in
ecology. We investigated diversity patterns (species richness, composition
and number of captures) of understorey bird assemblages in Amazonian
unflooded (terra firme) forests. We sought to understand whether
understorey bird assemblages in distinct areas of endemism show distinct
patterns of diversity, and whether species replacements among areas of
endemism occur while the proportion of species within guilds remains
stable. Location: Amazonia. Taxon: Understorey birds. Methods: To
investigate diversity patterns, we compiled studies that mist-netted birds
at 11 regions across seven Amazonian areas of endemism. We used
coverage-based rarefaction curves, non-metric multidimensional scaling
(NMDS) and created a heatmap based on the proportion of captures in each
area of endemism to access patterns of richness, composition and captures
of understorey birds, respectively. The relative variance (RVgp index) was
calculated to investigate the existence of guild proportionality within
each area of endemism. Results: Bird assemblages diverged across the seven
areas of endemism, in terms of species richness, composition and captures.
However, the proportion of species and individuals within guilds was
similar among areas of endemism, indicating that species replacements
across areas of endemism occur while maintaining the same ecological
functions. Guild proportionality suggests that interspecific competition
and resource availability are more important than environmental
heterogeneity in structuring understorey bird assemblages. Main
conclusions: The similar proportion of species within guilds suggest that
interspecific competition and resource availability are more important
than environmental heterogeneity in structuring local assemblages,
possibly via a process of limiting similarity in morphological and
functional traits. The observed congruent structure in understorey bird
assemblages across areas of endemism shows that coupled historical and
ecological processes, operating at local to large scales, have led to
current patterns of diversity and composition in Amazonian bird
communities.