Aims: Understanding how historical and ecological (species interactions) factors affect species and shape community structure is a fundamental goal in ecology. However, these two components are difficult to disentangle and are often confounded. We address the influence of these factors in governing the structure of bird assemblages. Location: Southeastern Australia. Taxon: The Meliphagoidea superfamily. Methods: By adopting a semi-experimental approach (i.e. high vs low interference competition), we examine the influence of a genus (Manorina) of honeyeater species that is well known for its hyper-aggressiveness and strong competitive capacity on the phylogenetic and functional structure of local assemblages across three different habitats (eucalypt woodlands, mallee and cleared habitat). We applied a model that explicitly incorporates the effects of neutral colonization and local extinction in shaping community structure and estimated the contributions of niche-based and neutral processes to community assembly using the STEPCAM technique. Results: Communities with the presence of Manorina species were characterized by faster rates of colonization and local extinction and exhibited a higher degree of phylogenetic clustering than communities without these despotic species, which suggests that this model not only mirrors habitat preferences, but also unintendedly accounts for the effect of biotic interactions. Stochastic processes had a lower contribution in the presence of Manorina species, whereas the role of filtering tended to be higher. We observed habitat differences in terms of functional (but not phylogenetic) structure, with more functionally clustered assemblages in the cleared habitat. Main Conclusions: Although recent studies have suggested that neutral-species processes are sufficient to explain local assemblage phylogenetic structure, our capacity to isolate them from contemporary ecological processes is still limited. This study also reinforces the idea that biotic interactions can also lead to patterns of underdispersion and thus, assumptions behind null model approaches for community assembly should be carefully considered in each case., Peer reviewed

Aim: Australian woodlands have been intensively cleared since European settlement and, in parallel, many species of birds inhabiting this habitat type have experienced a marked decline. Conversely, some species such as noisy miner Manorina melanocephala respond positively to habitat disturbance and due to their hyper-aggressiveness can end up driving away specialized and fragmentation-sensitive species. Recent studies have suggested that the negative impact of miners is exacerbated by means of synergistic interactions between these and other aggressive species, including nest predators. However, it is not clear if these positive associations arise through similar habitat requirements or due to potential mutual benefits (‘facilitation effects’), which should predominate in harsh environments as the stress-gradient hypothesis (SGH) predicts. Location: Eastern Australia. Methods: We combined a multi-season community N-mixture model and joint species distribution models within the Hierarchical Modelling of Species Communities framework to examine species co-occurrence patterns after accounting for imperfect detection and the influence of environmental variables. We then explored how the balance between positive and negative associations varied along an abiotic stress gradient and whether species-to-species associations were non-randomly distributed with respect to species traits. Results: No significant associations were detected; we only found tentative associations (posterior probability 85%) in a low proportion of species pairs (~4%). Although most non-random (tentative) associations were negative, these were weaker and less consistent across models than the positive ones. Five medium-sized species of swooping birds including the noisy miner monopolized virtually all positive associations. Communities from low-productivity environments tended to show a lower degree of overall (community-level) competitiveness than those located in less stressful (more productive) environments, which supports the SGH. There was no significant relationship between species trait dissimilarity and species-to-species association's strength. Main Conclusions: Our results suggest that aggressive species like miners, kookaburras, lorikeets, magpies and butcherbirds can form potential synergies with each other that may intensify the direct negative influence of each species on small-sized songbirds. Since these species thrive in anthropized landscapes and have drastically increased their numbers in some regions, their associative potential should be considered in conservation actions., Peer reviewed

[Aim] Variation in community composition along environmental gradients provides crucial information for identifying zones where species turnover is rapid and to ascertain whether compositional changes occur gradually or rather abruptly. We examined changes in bird community composition along three bioclimatic transects in Australia to test whether drivers of species turnover are consistent, rather than spatially contingent, across biologically contrasting ecosystems. We also detected potential transition zones associated with environmental thresholds and determined whether certain abiotic conditions promote a higher rate of community compositional turnover., [Location] Mainland Australia., [Taxon] Terrestrial birds., [Methods] We applied multivariate community analysis, generalised dissimilarity modelling (GDM) and threshold indicator taxa analysis (TITAN)., [Results] We observed that environmental variables are better predictors of community composition than spatial distance, which indicates that species sorting, rather than dispersal, plays a key role in structuring Australian avian communities. Annual precipitation constitutes a key driver of species turnover regardless of the analysed transect. The most humid landscapes and those with a higher tree canopy show lower spatial heterogeneity in community composition compared to those with less benign environmental conditions (e.g., dryer environments). TITAN detected significant transition points and supported the results obtained using GDM, which suggests that bird composition change along the gradients is not monotonic., [Main Conclusions] Our results suggest that avian beta diversity increases with increasing environmental harshness, presumably through changes in the relative importance of stochastic versus deterministic processes. The obtained findings show that open forests and woodlands are extremely important ecosystems on this continent and deserve special attention in terms of conservation due to their vulnerability to global change. Lastly, this study exemplifies the value of combining community- and taxon-based analyses to identify and interpret community thresholds, which can serve to pinpoint targets for preserving biodiversity., VGN was supported by the ‘Ramón y Cajal’ program (ref. RYC2019-026703-I), the research grants COMEVO (ref. PID2021-123304NA-I00) and BIODYN (ref. CNS2023-144066) of the Spanish Ministry of Science, Innovation and Universities (Agencia Estatal de Investigación AEI/10.13039/501100011033) and the European Union (‘Next Generation EU’), and a travel grant for guest researchers from the Swiss National Foundation SNF (ref. IZSEZ0_218541)., Peer reviewed

Theory predicts that selection against maladaptive hybridization leads to divergence of sexual characters in co-occurring closely related species. Consequently, signal disparity should be greater between sympatric vs. allopatric lineage pairs. However, this pattern may also result from species sorting or the greater evolutionary age of sympatric pairs. We used species pairs comparisons to examine the existence of acoustic divergence in a Neotropical montane radiation, the Rhinocryptidae, whose members tend to occupy different elevational ranges. Most rhinocryptids exhibit conservative morphology and are only differentiated by song attributes. Our results show that sympatric species pairs that overlap in elevation exhibited overall greater song divergence compared to allopatric species pairs after controlling for morphological differences, age and phylogenetic effects. Song divergence decreased when excluding sympatric pairs that do not overlap in elevation, suggesting that selection for improved species identification between co-occurring (syntopic) species accentuates signal differentiation. Comparative evolutionary models of signal differentiation over time revealed a similar pattern, which suggests that sexual selection in syntopy might have driven reproductive character displacement in this radiation. We conclude that selection against the production of unfit hybrids could favor acoustic traits that reliably signal species identity in tropical environments where many taxa are poorly differentiated by visual attributes., V.G.N. was supported by the “Ramón y Cajal” program (ref. RYC2019-026703-I) and the research grants COMEVO (ref. PID2021-123304NA-I00) and BIODYN (ref. CNS2023-144066) of the Spanish Ministry of Science and Innovation-Agencia Estatal de Investigación and the European Union. M.R.R. was supported by a “María Zambrano” fellowship (Spanish Ministry of Universities and Next Generation-EU)., Peer reviewed

Larks (Alaudidae) constitute one of the avian families best adapted to xeric environments, having colonized a wide suite of open habitats including deserts. Although their highest diversity is in Africa, larks occur on all nonpolar continents. We tested whether larks exhibit exceptional and/or correlated shifts in the tempos of speciation and ecological trait diversification in the face of open ecological space. We employed a near-complete phylogeny and a morphological dataset including several recently recognized species. We found homogeneity in diversification dynamics across the family and evidence for a diversity‐dependent slowdown in cladogenesis, which indicates that Alaudidae may approach their ‘ecological limit’. We did not observe an early burst in phenotypic diversification, as would be expected in a ‘classic’ adaptive radiation. Our findings suggest that the morphology of larks shows a high level of evolutionary conservatism and overall lack of ecomorphological convergence: ecological variables (diet and habitat)—which by contrast display a higher lability—explain little of shape/size variation except beak shape. Both adaptation to aridity and dietary transitions have evolved independently in multiple lineages across subfamilies. This study supports the idea that continental radiations in open habitats may reach an equilibrium faster than those in tropical forests, due to differences in ecological opportunities., V.G.N. was supported by the ‘Ramón y Cajal’ programme (ref. RYC2019-026703-I) and the research project COMEVO (ref. PID2021-123304NA-I00) of the Spanish Ministry of Science and Innovation. P.A. was supported by the National Swedish Research Council (grant No. 2019-04486) and the Jornvall Foundation., Peer reviewed