Avianβ-diversity along an urbanization gradient in Taipei metropolitan area

Abstract

Urbanization can alter species composition, ecosystem function, and phylogenetic structure. This study integrated avian functional trait and phylogenetic data to examine taxonomic, phylogenetic, and functional β-diversity across 143 bird assemblages along an urbanization gradient in the Taipei metropolitan area. We further partitioned β-diversity into turnover and nestedness components to investigate patterns and correlations among three dimensions β-diversity. In addition, we evaluated the effects of urban landscape characteristics, including green, blue, and gray spaces, as well as landscape compositional heterogeneity, on each dimension of β-diversity. Our results showed that taxonomic and phylogenetic β-diversity were primarily driven by turnover, whereas functional β-diversity was dominated by nestedness.

Keywords：Urbanization, β-diversity, Taipei metropolitan area, phylogenetic diversity , functional diversity

Methodology and Implementation Steps

We systematically surveyed bird assemblages across 143 plots in the Taipei Metropolitan Area. To represent the urbanization gradient, six habitat types were selected: commercial areas, built-up residential areas, urban parks, riverside lawns, agricultural areas, and forests, encompassing environments from the urban core to natural landscapes.

Bird surveys were conducted at each plot to obtain species composition. Taxonomic diversity was derived from field survey data, while phylogenetic and functional diversity were quantified by integrating the global avian phylogeny of 9,993 bird species (Jetz et al. 2012) and the Taiwan Bird Trait Dataset (Fu et al. 2024). These datasets were used to calculate phylogenetic and functional β-diversity across the urbanization gradient.

Species turnover represents the replacement of species among sites, indicating that different locations harbor distinct species assemblages, whereas nestedness reflects situations in which species assemblages at one site constitute a subset of those at richer sites. Because these two components imply different ecological processes and conservation strategies, β-diversity was partitioned into turnover and nestedness components following Baselga (2010) to examine the patterns and correlations among taxonomic, phylogenetic, and functional β-diversity along the urbanization gradient.

Environmental analyses incorporated three major urban landscape characteristics: green space (vegetation cover), blue space (aquatic environments), and gray space (impervious surface cover). Landscape compositional heterogeneity and spatial distance among sampling sites were also included as explanatory variables. We applied Generalized Dissimilarity Modeling (GDM) to evaluate the relative contributions of environmental and spatial factors to patterns of bird β-diversity across the urbanization gradient.

Innovation and Cross-Disciplinary Collaboration

This study integrated the Taiwan Bird Trait Dataset, the global avian phylogenetic framework, and urban bird assemblage data to simultaneously examine taxonomic, functional, and phylogenetic β-diversity, together with their turnover and nestedness components. By establishing an integrated analytical framework for assessing the impacts of urbanization on biodiversity, this interdisciplinary research combines ecological surveys, functional trait analysis, bioinformatics, phylogenetics, and landscape ecology. The findings not only advance the theoretical understanding of urban ecology but also provide a quantitative scientific basis for urban biodiversity conservation and sustainable urban planning.

Expected Results and Contributions

In response to the rapid pace of global urbanization, urban ecosystems have become increasingly important for biodiversity conservation and sustainable urban development. This study not only fills a critical knowledge gap by providing empirical evidence from subtropical urban ecosystems, thereby enhancing the international visibility of Taiwan's urban ecology research, but also offers a scientific basis for urban biodiversity conservation. Our findings demonstrate that preserving less urbanized areas and increasing landscape heterogeneity within cities can help maintain avian β-diversity. These results are consistent with the international objectives of Sustainable Development Goal 11 (SDG 11) and Target 12 of the Kunming–Montreal Global Biodiversity Framework, supporting the implementation of Nature-based Solutions to strengthen urban ecological resilience.