Urbanization drives biotic homogenization of the avian community in China.

Urbanization-driven biotic homogenization has been recorded in various ecosystems on local and global scales; however, it is largely unexplored in developing countries. Empirical studies on different taxa and bioregions show conflicting results (i.e. biotic homogenization vs. biotic differentiation); the extent to which the community composition changes in response to anthropogenic disturbances and the factors governing this process, therefore, require elucidation. Here, we used a compiled database of 760 bird species in China to quantify the multiple-site ß-diversity and fitted distance decay in pairwise ß-diversities between natural and urban assemblages to assess whether urbanization had driven biotic homogenization. We used generalized dissimilarity models (GDM) to elucidate the roles of spatial and environmental factors in avian community dissimilarities before and after urbanization. The multiple-site ß-diversities among urban assemblages were markedly lower than those among natural assemblages, and the distance decays in pairwise similarities in natural assemblages were more rapid. These results were consistent among taxonomic, phylogenetic, and functional aspects, supporting a general biotic homogenization driven by urbanization. The GDM results indicated that geographical distance and temperature were the dominant predictors of avian community dissimilarity. However, the contribution of geographical distance and climatic factors decreased in explaining compositional dissimilarities in urban assemblages. Geographical and environmental distances accounted for much lower variations in compositional dissimilarities in urban than in natural assemblages, implying a potential risk of uncertainty in model predictions under further climate change and anthropogenic disturbances. Our study concludes that taxonomic, phylogenetic, and functional dimensions elucidate urbanization-driven biotic homogenization in China.

Geographic variations in eco-evolutionary factors governing urban birds: The case of university campuses in China.

Urbanization alters natural habitats, restructures biotic communities and serves as a filter for selecting species from regional species pools. However, empirical evidence of the specific traits that allow species to persist in urban areas yields mixed results. More importantly, it remains unclear which traits are widespread for species utilizing urban spaces (urban utilizers) and which are environment-dependent traits. Using 745 bird species from 287 university/institute campuses in 74 cities and their species pools across China, we tested whether species that occur in urban areas are correlated with regards to their biological (body mass, beak shape, flight capacity and clutch size), ecological (diet diversity, niche width and habitat breadth), behavioural (foraging innovation) and evolutionary (diversification rate) attributes. We used Bayesian phylogenetic generalized linear mixed models to disentangle the relative roles of these predictors further, and to determine the extent to which the effects of these predictors varied among different cities. We found that urban birds were more phylogenetically clustered than expected by chance, and were generally characterized by a larger habitat breadth, faster diversification rate, more behavioural innovation and smaller body size. Notably, the relative effects of the attributes in explaining urban bird communities varied with city temperature and elevation, indicating that the filters used to determine urban species were environment dependent. We conclude that, while urban birds are typically small-sized, generalists, innovative and rapidly diversifying, the key traits that allow them to thrive vary spatially, depending on the climatic and topographic conditions of the city. These findings emphasize the importance of studying species communities within specific cities to better understand the contextual dependencies of key traits that are filtered by urban environments.

A global assessment of Bergmann's rule in mammals and birds.

Bergmann's rule states that endotherms have a large body size in high latitudes and cold climates. However, previous empirical studies have reported mixed evidence on the relationships between body size and latitude, raising the question of why some clades of endotherms follow Bergmann's rule, whereas others do not. Here, we synthesized the interspecific relationships between body size and latitude among 16,187 endothermic species (5422 mammals and 10,765 birds) using Bayesian phylogenetic generalized linear mixed models to examine the strength and magnitude of Bergmann's rule. We further assessed the effect of biological and ecological factors (i.e., body mass categories, dietary guild, winter activity, habitat openness, and climate zone) on the variations in the body mass-latitude relationships by adding an interaction term in the models. Our results revealed a generally weak but significant adherence to Bergmann's rule among all endotherms at the global scale. Despite taxonomic variation in the strength of Bergmann's rule, the body mass of species within most animal orders showed an increasing trend toward high latitudes. Generally, large-bodied, temperate species, non-hibernating mammals, and migratory and open-habitat birds tend to conform to Bergmann's rule more than their relatives do. Our results suggest that whether Bergmann's rule applies to a particular taxon is mediated by not only geographic and biological features, but also potential alternate strategies that species might have for thermoregulation. Future studies could explore the potential of integrating comprehensive trait data into phylogenetic comparative analysis to re-assess the classic ecogeographic rules on a global scale.

Historical connectivity and environmental filtering jointly determine the freshwater fish assemblages on Taiwan and Hainan Islands of China.

The biotas of Taiwan and Hainan Islands are of continental origin, but the manner with which historical and ecological factors shaped these insular species is still unclear. Here, we used freshwater fish as a model to fill this gap by quantifying the phylogenetic structure of the insular faunas and disentangling the relative contribution of potential drivers. Firstly, we used clustering and ordination analyses to identify regional species pools. To test whether the insular freshwater fish faunas were phylogenetically clustered or overdispersed, we calculated the net relatedness index (NRI) and the nearest taxon index (NTI). Finally, we implemented logistic regressions to disentangle the relative importance of species attributes (i.e., maximum body length, climatic niche dissimilarity [ND], and diversification) and historical connectivity (HC) in explaining the insular faunas. Our results showed that the most possible species pools of Taiwan are Zhejiang and Fujian provinces, and those of Hainan are Guangdong and Guangxi provinces. These insular faunas showed random phylogenetic structures in terms of NRI values. According to the NTI values, however, the Taiwanese fauna displayed more phylogenetic clustering, while the Hainanese one was more overdispersed. Both the standard and phylogenetic logistic regressions identified HC and climatic ND as the 2 top explanatory variables for species assemblages on these islands. Our reconstruction of the paleo-connected drainage basins provides insight into how historical processes and ecological factors interact to shape the freshwater fish fauna of the East Asian islands.

Transforming absolute value to categorical choice in primate superior colliculus during value-based decision making.

Value-based decision making involves choosing from multiple options with different values. Despite extensive studies on value representation in various brain regions, the neural mechanism for how multiple value options are converted to motor actions remains unclear. To study this, we developed a multi-value foraging task with varying menu of items in non-human primates using eye movements that dissociates value and choice, and conducted electrophysiological recording in the midbrain superior colliculus (SC). SC neurons encoded "absolute" value, independent of available options, during late fixation. In addition, SC neurons also represent value threshold, modulated by available options, different from conventional motor threshold. Electrical stimulation of SC neurons biased choices in a manner predicted by the difference between the value representation and the value threshold. These results reveal a neural mechanism directly transforming absolute values to categorical choices within SC, supporting highly efficient value-based decision making critical for real-world economic behaviors.