Temporal persistence of taxonomic and functional composition in bird communities of urban areas: an evaluation after a 6-year gap in data collection

Urbanization reduces diversity, simplifies community and filter bird species based on their functional traits in a tropical city

Understanding how organisms are coping with major changes imposed by urban intensification is a complex task. In fact, our understanding of the impacts of urbanization on biodiversity is scarce in the global south compared to the north. In this study, we evaluated how bird communities are affected by impact of urban intensification in a tropical city. Thus, we assessed whether increased urban intensification 1) jeopardizes bird diversity (taking into account taxonomic-TD, phylogenetic-PD, and functional-FD dimensions), 2) drives changes in bird community composition and enables the detection of indicator species of such impact, and 3) leads to changes in bird functional traits linked to reproduction, resource acquisition, and survival. We found that urban intensification has a direct impact on the bird community, reducing all three types of diversity. Communities in areas of greater urban intensity are represented by fewer species, and these species are PD and FD less distinct. In addition, we detected at least ten species of areas of lower urban intensity that proved to be more sensitive to urban intensification. With regard to bird traits, we found no significant responses from reproductive, habitat use and feeding variables. Body weight and tail length were the only variables with significant results, with higher urbanization intensity areas selecting for species with lower weights and longer tails. Given the global biodiversity loss we are observing, this information can guide urban managers and planners in designing urban landscapes to maintain biodiversity in cities.

Data from public and governmental databases show that a large proportion of the regional animal species pool occur in cities in Germany

Cities have been shown to be biodiverse, but it is unclear what fraction of a regional species pool can live within city borders and how this differs between taxa. Among animals, most research has focused on a few well-studied taxa, such as birds or butterflies. For other species, progress is limited by the paucity of data. We used species occurrence data for 11 taxa and 23 German cities from the Global Biodiversity Information Facility (GBIF) and the different German states, in a 50-km buffer around the city centre, to investigate what proportion of species of the regional species pools also occur in cities. While data could be obtained for all cities from GBIF, state databases only provided data for a subset of cities. Sample coverage of data from GBIF was higher across all taxa than of the state databases. For each database and taxon, we analysed (i) all cities where the number of occurrences of a taxon was >50 and (ii) only those cities where additionally sample coverage was >0.85. Across all taxa studied on average, 44.9 ± 7.2% (GBIF) and 40.8 ± 9.6% (German states) of the species of the regional species pool were also found in cities. When all cities were considered together, more than 76% of all species occurred within city borders. Our results show that German cities harbour a large part of the regional diversity of different taxa when city borders rather than the city centre is considered. This opens up ample opportunities for conservation and for fostering human–nature relationships.