Effect of seed removal by ants on the host-epiphyte associations in a tropical dry forest of central Mexico

Vascular epiphytes account for around 9 % of vascular plants worldwide. The presence of epiphytic flora increases the species richness and structural complexity of forests, as well as providing resources for fauna and offering new sources and routes for nutrient and water cycling in the forest. In a recent study published in AoBP, Vergara-Torres et al. focussed on the relationship between epiphytic bromeliad species (Tillandsia spp.) and ants in tropical dry forests of central Mexico. In addition to being considered primary consumers of seeds, ants can act as primary and secondary agents of dispersion, since they collect seeds that have fallen from the trees or have been dispersed by the wind. The aim of this study was to experimentally test whether seed removal activity is higher in tree species with smaller epiphyte loads compared to those with greater epiphyte loads.

Seed removal differed among hosts and different soil substrates in the forest. Relating seed removal to the abundance of arboreal ants, the most consistent pattern was that lower seed removal was related to lower ant abundance, while high seed removal was associated with intermediate to high ant abundance. Epiphyte seed removal by ants influences epiphyte abundance and can contribute considerably to a failure to establish, since it diminishes the quantity of seeds available for germination and establishment. Further exploration of the mechanisms of association between trees and ants will help us to better understand the structure of epiphytic plant communities.