COS 26-2 - Vertebrate urine is an alternative food source for canopy but not ground ants

Abstract: Ants are among the most abundant groups of arthropods, and approximately half of all ant species are associated with forest canopies. Canopy ants are faced with a more nitrogen-limited environment compared to ground ants, due to their reliance on nitrogen-poor plant and insect exudates. Despite prior work establishing that some genera and species consume vertebrate urine and can use symbiotic bacteria to extract nitrogen from this food source, we have little knowledge about the use of vertebrate urine as a source of nitrogen in canopy ants or the relative preference for urine between ground and canopy ants. We conducted a field experiment in a lowland tropical rainforest in southern China to test for vertical stratification in ant preference for sugar and urine, setting baited pitfall traps on the ground and in the canopy with the use of a canopy crane. We found distinct vertical stratification in the use of urine, with higher richness and abundance of ants in sugar baits on the ground, and a higher abundance of ants in urine baits in the canopy. Furthermore, the composition of captured ants differentiated according to both vertical stratum and bait type. This distinct vertical stratification of niche preference may represent an important case of niche partitioning that contributes to high ant species diversity in tropical rainforests as well as high species turnover between ground and canopy strata. The preference of canopy ants for vertebrate urine also highlights the importance of interspecific interactions across highly unrelated animal taxa and emphasizes the need for a holistic understanding of biological networks to effectively conserve threatened tropical forest communities.