ATBC Online Web Program

Direct and indirect effects of ants on epiphytes in coffee agroecosystems in Mexico and Ethiopia

Monday, 24 June 2013: 16:30
Americas B-C (Herradura San Jose)
Jörgen Rudolphi , Department of Ecology, Environment and Plant Sciences, Stockholm University, Sweden
Kristoffer Hylander , Department of Ecology, Environment and Plant Sciences, Stockholm University, Sweden
Stacy M Philpott , Environmental Studies, University of California, Santa Cruz
Ants and epiphytic plants are among the most dominant taxa in tropical ecosystems. Ants are important biodiversity components not only because of their abundance, but also because they often act as ecosystem engineers. Epiphytes are sensitive indicators of microclimate, and provide essential habitat and food for rainforest fauna. Because the natural tropical forests are continuously disappearing shaded agroecosystems (e.g. coffee and cacao) may be increasingly important for many ant and epiphyte species. Interactions between ants and epiphytes in these systems have however been very little studied. Studies from other tropical ecosystems show that ants can purportedly disperse seeds of epiphytes, but also negatively affect epiphytes either directly by removing seeds or seedlings or indirectly as a result of their activity. We investigated how the vascular epiphyte community was affected by two dominant arboreal ant species nesting in shade trees in coffee agroecosystems – one in Chiapas, Mexico and one in Oromia region, Ethiopia. In the Mexican coffee agroecosystem we sampled epiphytes on trees with and without nests of Azteca instabilis and in Ethiopia we sampled on trees with and without nests of Crematogaster cf. buchneri. Vascular epiphyte richness increased with increasing cover of epiphytic bryophytes in both of the regions. Using structural equation modeling (SEM), we found that Azteca indirectly affected epiphyte richness negatively via its negative impact on bryophyte cover. Interestingly, also Crematogaster in Ethiopia had an indirect negative effect on epiphyte species richness via bryophyte cover. We found no direct effects of ant presence on vascular epiphyte species composition or richness in any of the two regions. Field experiments confirmed that the ants actively removed bryophytes from tree trunks. Our results indicate that arboreal ants affect the distribution patterns of vascular epiphytes, and that this impact is widespread in tropical agroecosystems.