Preference for mammalian urine is higher in the canopy than on the ground in a tropical rainforest ant community in Yunnan, China

Ants are among the most abundant groups of arthropods, and approximately half of all ant species are associated with forest canopies. The forest canopy environment is distinct from the understory and forest floor, and vertical stratification in environmental conditions shapes species assembly and organismal traits and behaviors across taxa in forest communities. Canopy ants are faced with a more nitrogen-limited environment compared with ground ants because of their reliance on nitrogen-poor plant and insect exudates. Despite prior work suggesting that some ant species consume mammalian urine and use symbiotic bacteria to extract nitrogen, we have little knowledge about the consumption of urine in canopy ants or the relative preference for urine between ground and canopy ants. We conducted an observational field experiment in a lowland tropical rainforest in southern China to test for vertical stratification in ant preference for sugar and urine, setting ground and canopy baited pitfall traps with the use of a canopy crane. We found distinct vertical stratification in the use of urine, with higher richness and abundance in sugar baits on the ground, and a higher abundance 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 mammalian 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.

Methods
See the associated manuscript for detailed methods of data collection.

In brief, ants were collected in the canopy and the ground from (or below) 12 trees in the Xishuangbanna National Nature Reserve in Xishuangbanna Dai Autonomous Prefecture, Yunnan Province, China, using liquid baited pitfall traps with three different food sources (sugar water, urine water, and water).