Baseline for evaluating the rainforest intactness using volant and non-volant mammal eco-behavioural traits in a UNESCO Biosphere Reserve

Context Volant and non-volant mammals differ in their sensitivity to environmental and anthropogenic pressures, making species traits central to understanding biodiversity erosion. However, the extent to which forest structure predicts faunal composition remains unclear. Aims We tested how eco-behavioural traits and rainforest structure jointly influence detection and occupancy in mammal assemblages, and whether habitat characteristics reliably explain variation in community composition. Methods Over 12 months, we combined ground and arboreal camera trapping, bat flight-performance indices, and vegetation measurements in mature lowland forest in the Yangambi Biosphere Reserve, Democratic Republic of the Congo. Single-season multi-species occupancy models were used to estimate variation in detection and occupancy as a function of species traits and habitat characteristics while accounting for imperfect detection. Key results Detection probability declined sharply with increasing body mass and sociality (Pi = 0.06, β = −39.08), indicating non-random depletion of large-bodied, group-living mammals consistent with trait-mediated filtering under human pressure. Stem density positively affected occupancy (ψ = 0.30, β = 9.06), but this effect was insufficient to offset evidence of defaunation, showing a mismatch between forest condition and assemblage composition. By contrast, bats showed high occupancy (ψ = 0.85) across structural gradients (β = −1.92), whereas detection probability (Pi = 0.162) was unrelated to flight traits, suggesting greater ecological flexibility. Conclusions Non-volant mammal assemblages were shaped primarily by trait-mediated filtering rather than forest structure alone. By contrast, bats maintained high occupancy across heterogeneous habitats, supporting functional connectivity and showing contrasting responses to environmental change in tropical forests. Implications Structural metrics alone are insufficient proxies for ecosystem intactness. Integrating species traits with occupancy-based approaches can provide early-warning indicators of biodiversity change and support resilience-based management and restoration of tropical forests.