Hoenle, P.O., Schumacher, N.C., Fibich, P., Posman, A., Biul, M. & Klimes, P.

Competition for food and nesting resources in arboreal ant communities is higher in lowland than in mid-elevation rainforests

Competition is one of the most intriguing ecological concepts as it is ubiquitous in nature but challenging to quantify. Tropical arboreal ants are known to compete for food resources and nesting space, with some species maintaining large colonies and territories. However, little is known about how elevation and forest stratification influence this competition at the community level. We hypothesize that ant competition is mediated by temperature and therefore expect it to increase in the warmer lowland rainforests compared with mid-elevations. We also expect that temperature should lead to higher competition in forest canopies compared with smaller understorey trees due to warmer microclimate. We measured resource competition by placing baits (food resource) and bamboo cavities (nesting resource) in the natural rainforest of Mt. Wilhelm, Papua New Guinea. These artificial resources were distributed in both canopy and understorey trees across four sites in each of two locations: lowland (ca. 200 m above sea level, a.s.l.) and mid-elevation (ca. 900 m a.s.l.) forests. We recorded a total of 89 ant species on the baits and 33 species inside the cavities, and each resource measured a complementary part of the community. Mid-elevation sites had significantly higher ant species diversity and species co-occurrence on baits but much lower occupation and abundance both on the baits and in the cavities. This indicated a stronger competition in the lowland than mid-elevation communities, despite the higher ant diversity in the latter. Canopies showed a higher competition than understorey, reflected by higher occupancies of both cavities and baits. Moreover, behaviourally dominant territorial species were much more common on baits in the lowlands than mid-elevations. While the two locations did not differ in the forest structure (i.e., tree size, lianas, and dead wood), the lowlands were ca. 4 °C warmer. We hypothesize that the lowland dominance of aggressive ants, possibly maintained by this warmer climate, plays an underappreciated role in elevational community assembly. We conclude that temperature-mediated competition is thus the most likely driver of the observed differences in ant community structure between the two elevations.

Open access, licensed under CC BY 4.0. © 2025 The Author(s).

Altitude, Formicidae, canopy ants, climate, interspecific competition, Hymenoptera, manipulative experiment, resource availability, species coexistence, tropical forest, vertical stratification.