Patch and Landscape Predictors of Mammal Diversity and Their Trait‐Relationships in the Largest Atlantic Forest Island in Brazil

ABSTRACT Urban expansion threatens biodiversity, especially on islands where native habitats and biological populations are naturally restricted. To understand how biodiversity responds to ongoing urban‐driven landscape changes, we assessed how landscape configuration and composition shape mammal diversity on Santa Catarina Island—the largest Atlantic Forest island in Brazil—still largely forested. Between 2019 and 2022, we deployed camera traps at 22 sampling sites (> 1 km apart) across nine protected forest patches. Landscape metrics related to forest area, shape, isolation, and surrounding land cover were evaluated for their relationship with species richness, abundance, composition, and functional traits. Over 6569 camera trap days, we obtained 4151 independent records from 11 species. Richness decreased with surrounding unvegetated and urban matrix, while abundance peaked in smaller and more isolated patches, suggesting opportunistic species dominate these landscapes. Assemblage composition shifted from species‐rich core forests to depauperate edge patches dominated primarily by the Dasyprocta azarae , followed by the Didelphis aurita and small rodents. The carnivore guild was represented by a single detection of the semi‐aquatic Lontra longicaudis , reflecting the absence of native felids and potential detection limitations for elusive species. This trophic group showed no significant association with landscape variables in multivariate trait‐environment models, suggesting a current functional gap in predator roles. Our findings highlight the legacy of habitat loss, fragmentation, and defaunation. Without connectivity and top‐down ecological controls, the island risks transitioning to a functionally degraded state. Urgent landscape‐level planning is needed, including forest restoration, connectivity, and rewilding strategies to restore lost functional groups.