Functional Diversity in Tropical Mammals

Abstract

Functional diversity -- the range, distribution, and abundance of functional traits within and among species assemblages-- determines ecosystem process rates and resilience to disturbance, yet remains poorly characterised for tropical mammal communities undergoing rapid land-use change. This study quantified functional diversity indices (functional richness FRic, functional evenness FEve, functional divergence FDiv, and community-weighted mean CWM traits) for mammal assemblages at 42 sites across a forest-to-agriculture land-use gradient in the Congo Basin, using camera trap data (12,840 trap-nights, 2019-2023), trait databases, and body mass measurements from 2,840 individuals of 84 species. Functional richness declined by 48.4 +/- 8.4% from intact forest to smallholder agriculture (F3,38 = 28.4, p < 0.001), driven primarily by the loss of large-bodied frugivores and seed dispersers (mean body mass > 10 kg). Community-weighted mean body mass declined from 12.4 +/- 3.2 kg in intact forest to 1.8 +/- 0.6 kg in degraded and agricultural sites. Functional redundancy -- the number of species sharing functional trait combinations -- was lowest in intact forest (mean 1.84 +/- 0.42 species per functional entity) and highest in degraded forest (2.84 +/- 0.62), indicating that intact forests support higher proportions of functionally unique species. Trait-based vulnerability modelling identified large body mass, low reproductive rate, and specialised dietary requirements as the strongest predictors of local extinction across the gradient (AUC = 0.84). These findings demonstrate that land-use intensification drives rapid functional homogenisation of Congo Basin mammal communities with direct consequences for seed dispersal, herbivory regulation, and forest regeneration.