Manna from heaven: refuse from the arboreal ant, Azteca trigona, connects above- and below-ground processes in a lowland tropical rainforest

Ecosystem processes in terrestrial habits may be heavily influenced by consumer-driven linkages between aboveground and belowground systems. Consumption in aboveground food webs can have profound effects on belowground systems and processes such as decomposition, but the importance of such linkages are generally difficult to assess because the impacts and byproducts of consumer activity are often diffuse. Ants are likely important connectors of aboveground and belowground systems because colonies are often abundant, stationary and long-lived, and their wide and active foraging can produce large quantities of refuse concentrated in or near nests. Azteca trigona, a dominant arboreal ant in Panamanian lowland tropical forests, feeds on honeydew and insects and produces nutrient-rich refuse that regularly rains out the large, hanging, carton nests onto the leaf litter below. We used an observational study to test the prediction that decomposition is increased below A. trigona nests in refuse piles. Decomposition rates of both cellulose and wood were nearly 2-fold faster under nests than they were 10m away and the arthropod food webs below nests revealed greater abundances of detritivores and predators, such as springtails and spiders respectively, than communities 10m away. We further examined decomposition rates in a common garden experiment which revealed faster cellulose decomposition in refuse-addition plots than in either soil-addition or control plots; this suggests that refuse itself was the cause of the observational patterns. Our results indicate that A. trigona provides an important link between aboveground and belowground processes by creating decomposition hotspots and generating spatial variation in detrital communities.