Exploring the relationships between landscape connectivity and urban biodiversity: Insights from citizen science on pollinators and birds in Paris, France

Urban greening has emerged as a vital strategy to address biodiversity loss and promote sustainability. Enhancing landscape connectivity in cities is often cited as essential for facilitating species movement and supporting biodiversity. However, empirical validation remains scarce, particularly regarding the relative roles of habitat quantity and connectivity. This study investigates the effects of landscape connectivity and vegetation amount on urban biodiversity in Paris, France, using citizen science data on passerine birds and pollinators. Using citizen science data, we modeled ecological networks with graph theory to test three hypotheses: (H1) increased connectivity positively correlates with species richness and abundance, (H2) the connectivity-abundance relationship depends on species specialization, and (H3) connectivity influences bird community composition, favoring specialists in highly connected areas. Our results show that pollinator and bird richness is positively influenced by functional connectivity and vegetation cover. However, bird abundance is driven primarily by vegetation cover, with no overall effect of connectivity. Importantly, functional connectivity only has a significant positive effect when habitat patch size is considered; otherwise, its impact disappears or becomes negative. Species-level analyses revealed that some urban-adapted birds respond negatively to high connectivity, suggesting fragmentation may favor them. These findings underline the complexity of biodiversity responses to urban landscapes and the need to clarify connectivity estimation methods. The study highlights the importance of integrating habitat amount and species-specific ecology in urban planning to optimize green infrastructure for biodiversity.