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Does competition influence patterns of coexistence between closely related taxa? Here we address this question by analyzing patterns of range overlap between related species of birds ('sister pairs') co‐occurring on a tropical elevational gradient. We explicitly contrast the behavioral dimension of interspecific competition (interference competition) with similarity in resource acquisition traits (exploitative competition). Specifically, we ask whether elevational range overlap in 118 sister pairs that live along the Manu Transect in southeastern Peru is predicted by proxies for competition (intraspecific territorial behavior) or niche divergence (beak divergence and divergence times, an estimate of evolutionary age). We find that close relatives that defend year‐round territories tend to live in non‐overlapping elevational distributions, while close relatives that do not defend territories tend to broadly overlap in elevational distribution. In contrast, neither beak divergence nor evolutionary age was associated with patterns of range limitation. We interpret these findings as evidence that behavioral interactions – particularly direct territorial aggression – can be important in setting elevational range limits and preventing coexistence of closely related species, though this depends upon the extent to which intraspecific territorial behavior can be extended to territorial interactions between species. Our results suggest that interference competition can be an important driver of species range limits in diverse assemblages, and thus highlight the importance of considering behavioral dimensions of the niche in macroecological studies. [ABSTRACT FROM AUTHOR]

The Rufous Twistwing (Cnipodectes superrufus), a newly described Amazonian tyrant-flycatcher, is known from five specimens and five localities in Cuzco and western Madre de Dios departments, Peru. We report three additional specimens and eight new localities extending the known range of the species east across Dpto. Madre de Dios, Peru, into Dpto, Pando, Bolivia, and Acre State, Brazil. The new localities increase the distribution from ∼3.400 to -89.000 km² We collected biometric data from five individuals, made behavioral observations in the field, and recorded three separate types of vocalizations, two of which (including the song) were previously unknown. We provide quantitative description of these vocalizations, consider their function, and compare them with vocalizations of the only known congener, the Brownish Twistwing (Cnipodectes subbrunneus). Unique vocal repertoires support the classification of these two forms as sister species. The Rufous Twistwing resembles the Brownish Twistwing in producing loud vocalizations from regular song posts and both species appear to have a polygamous mating system. We provide further evidence consistent with the hypothesis the Rufous Twistwing is a Guadua bamboo specialist and recommend that it be listed as Vulnerable on the IUCN Red List. [ABSTRACT FROM AUTHOR]

Until recently thought to be secure (i.e. Least Concern), the Blue-headed Macaw is now classified as Endangered in the IUCN Red List, based on an apparent decline and a population estimate of <2500 mature individuals. We review published and unpublished sources, collating records from 61 localities in Peru, Brazil and Bolivia, and compiling information on habitat use, seasonality, group size, demography, and population density. We find the species to be associated with disturbed habitats at one site, but a broader analysis revealed no significant associations with forest type, riverine habitats, degree of disturbance or altitude. By mapping locality records, and accounting for discontinuities, we calculate an Extent of Occurrence of 460,000km2. Range-wide data on encounter rates and flock sizes suggest that the species is sedentary and gregarious, with an overall population density of one mature individual per 10–50km2. Our figures for range size and density (both highly conservative) indicate that the global population estimate should be revised upwards to 9200–46,000 mature individuals. Balanced against an increasing threat from trade, these data argue for a reversal in status to Vulnerable, with a shift to Near Threatened possible in future. Given these recent fluctuations in conservation status, the Blue-headed Macaw provides valuable insight into the difficulties of using IUCN Red List criteria to assess poorly known taxa. Red List assessments should be based on extensive reviews where possible, and analyses using Red List data should consider effects of data quality. [Copyright &y& Elsevier]

How the relative importance of community assembly processes varies with spatial scale is the focus of intensive debate, in part because inferring the scales at which specific niche-based processes act is difficult. One obstacle is that standard phylogenetic and functional diversity metrics may integrate the signals of multiple processes when combining separate niche axes into one variable (multiple-niche-axis metrics), potentially obscuring overlapping niche-based processes. We use simulations to evaluate the power of these metrics to detect competition and habitat filtering when these processes operate across multiple niche axes and vary in their relative importance. We then test for both processes at a range of spatial scales in a Neotropical bird assemblage. Simulations revealed that multiple-niche-axis metrics had low power to detect competition and habitat filtering when a mix of both processes acts across niche axes, whereas metrics focused on single-niche axes were better able to deal with this complexity. We found the same contrast in bird communities, where both competition and habitat filtering were detected at the scale of individual territories, but only by single-niche-axis metrics focused on specific niche axes (e.g., foraging traits). Our results suggest that multiple-niche-axis metrics may produce misleading evidence that niche-based processes are partitioned, particularly across scales, and highlight the importance of analyzing functional diversity patterns on individual niche axes when testing assembly models.