Rainforest conversion to monocultures favors generalist ants with large colonies

The conversion of natural ecosystems to agricultural land is one of the most important drivers of biodiversity decline worldwide, particularly in the tropics. Species loss is typically trait‐associated, leading to filtering of disturbance‐resistant species during community assembly, which affects ecosystem functioning and evolutionary potential of communities. To understand the ecological and phylogenetic impact of rainforest conversion to agricultural systems, we combine analysis of nesting habit, feeding habit, colony size, and body size of canopy ants (Formicidae) with a phylogenetic analysis of species collected in four land‐use systems in Sumatra, Indonesia: (1) lowland tropical rainforest, (2) jungle rubber (extensive rubber agroforest), and smallholder plantations of (3) rubber and (4) oil palm. Canopy ant communities in these land‐use systems differed in trait composition, with a larger proportion of generalist nesting and generalist‐omnivore feeding species in oil palm compared to rainforest and a larger proportion of generalist nesters and species with large colonies (>1000 individuals) in rubber than in rainforest. Traits of canopy ant communities in jungle rubber were more similar to those in rainforest than to those in rubber and oil palm plantations. In rainforest, mean pairwise phylogenetic distance was lower than expected for random community assembly, but did not differ from random in the other land‐use systems. Of the traits nesting habit, feeding habit, and colony size, only feeding habit exhibited phylogenetic signal. Our results show that rainforest conversion to agricultural systems is accompanied by shifts in trait composition of canopy ant communities. Further, our results argue against environmental filtering of closely related canopy ant species as the major community assembly mechanism in plantation systems, but suggest that the Sumatran lowland rainforests harbor recently diverged endemic ant species that are particularly vulnerable to rainforest conversion to agricultural systems. Given the importance of ants for tropical ecosystems, the ecological differences among ant communities along the land‐use gradient might have important consequences for ecosystem functioning and services in plantation systems.