Interactive effects of fire and habitat loss shape dietary trait structure of bird communities in tropical forests

Fire and habitat loss are major drivers of biodiversity change in tropical forests, yet their combined effects on functional traits remain poorly understood. We investigated how fire severity, fire extent, and forest cover jointly influence bird dietary traits across 15 Atlantic Forest landscapes in southeastern Brazil, each containing paired burned and unburned forest sites (30 sampling units). Birds were surveyed using point count methods, and community trait structure was quantified using community-weighted means (CWM) and variances (CWV) derived from continuous dietary traits (e.g., proportional use of different food resources), estimated through a nonparametric bootstrapping approach. We used generalized linear mixed models to assess the effects of fire and forest cover on these trait metrics. Both CWM and CWV were influenced by fire disturbance, with responses strongly modulated by forest cover, revealing non-additive and synergistic effects. Under high fire disturbance and low forest cover, trait convergence—expressed as reduced variability in fruit, nectar, and invertebrate consumption—indicating strong environmental filtering. Conversely, increased variance in seed consumption in burned forests suggested trait divergence consistent with limiting similarity under enhanced post-fire resource heterogeneity. These findings demonstrate that environmental filtering and limiting similarity can coexist along disturbance gradients, depending on both trait identity and landscape context. Our results highlight the value of trait-based approaches for detecting functional responses beyond species richness and reinforce the need to integrate fire management with habitat conservation to maintain functional integrity (i.e., the retention of community trait structure) in fire-susceptible tropical forests.