1-10 ants m -1 = 1/6 trail 10-20 ants m -1 = 2/6 trail 20-40 ants m -1 = 4/6 trail >40 ants m -1 = 6/6 trail Trail Score = sum of trails A B A B Figure 1. A) Schematic representation of a tree with ant trails. B) Ant trail on a branch. Figure 2. A) An O. smaragdina nest. B) sorting nest content. 0 10 20 30 40 50 60 0 1 2 3 4 5 6 0 1 2 3 4 5 6 0 1 2 3 4 5 Total nest volume in tree (L) Total ant biomass (g wet wt) Total ant biomass (g wet wt) Trail score Nest volume (L) Trail score Figure 3. Relation between trail score and total active nest volume in the tree (n= 16, R 2 = 0.85). Figure 4. Relation between nest volume and total ant biomass (n=77, R 2 =0.67). Figure 5. Total ant biomass as a function of trail score. Thick line represents median value and shaded area represents 95% credible interval. 0 50 100 150 200 250 0 200 400 600 800 1000 1200 1400 Acknowledgement This study was funded by the Danish Council for Inde- pendent Research. Table 1. Number of colonies, trees occupied, estimated biomass and number of workers in the plantation. Values in paren- theses represent standard deviation and square brackets represent colony range. Plantation data Number of colonies Trees occupied Total biomass (g wet weight) Number of workers* Area (ha) # Trees 5 40 8,428 (834) 1,065,931 (105,969) 0.42 76 [2-14] [666-2,977] [84,578-376,635] *Numbers of workers has been calculated from the mean weights of major and minor workers. Non-destructive estimation of Oecophylla smaragdina colony biomass Christian Pinkalski 1 (CASP@dmu.dk), Christian Damgaard 1 , Karl-Martin Vagn Jensen 2 , Rene Gislum 2 , Renkang Peng 3 & Joachim Ofenberg 1 1 Aarhus University, Department of Bioscience, Vejlsøvej 25, DK-8600 Silkeborg, Denmark 2 Aarhus University, Department of Agroecology, Forsøgsvej 1, DK-4200 Slagelse, Denmark 3 RIEL, Charles Darwin University, Darwin NT 0909, Australia References [1] Sanders, D. & van Veen, F.J.F. 2011. Ecosystem engineering and predation: the multi-trophic impact of two ant species. Journal of Animal Ecology 80:569-576. [2] Folgarait, P. 1998. Ant biodiversity and its relationship to ecosystem functioning: a review. Biodiversity and Conservation 7:1221-1244. [3] Hölldobler, B. & Wilson, E.O. 1990. The Ants. Belknap Press of Harvard University Press, Cambridge, USA. [4] Fittkau, E.J. & Klinge, H. 1973. On Biomass and Trophic Structure of the Central Amazonian Rain Forest Ecosystem. Biotropica 5:2-14. Introduction Ants have a signifcant infuence on ecosystem functioning [1]. Feeding on several trophic levels, ants serve as conduits for the fow of nutrients [2]. However, a fully understanding of their functional importance has been hampered by limit- ed availability of data on ant abundance. The weaver ant Oecophylla smaragdina is a predatory species that construct nests of leaves in the canopy. The colonies can reach huge population sizes, span large territories and may consist of hundreds of nests [3]. The nests are distinctive, exposed and can readily be sampled for measurement of volume and nest content. Quantifying the abundance of O. smaragdina can provide a general insight into the environ- mental impact of ants. Objective Develop a swift method by which the biomass of O. smaragdina colonies could be estimated non-destructively. Methods O. smaragdina biomass was estimated by means of two sub-models: Model 1) Predicting the total ant nest volume in a host tree by scoring the number of ant trails according to their density in 16 trees and subse- quently measuring the volume of all the nests in the trees (fgure 1). Model 2) Predicting the biomass content as a function of nest volume by measuring the volume of 77 nests and subsequently deter- mine their biomass content (fgure 2). The end product was a method with by direct assessment of colony size (biomass) could be performed by assessing the trail score in trees inhabited by O. smaragdina. Through a Bayesian latent variable model, quantitative assessments of the uncertainties in the estimates were made. Based on the developed model, the biomass in all trees hosting O. smaragdina was estimated in a mango plantation in Darwin, Australia. Results Trail scores ranged from 0.5 on trees with few and low density ant trails, to 5 on trees where almost every branch were occupied by an ant trail (fgure 3). The relation between nest volume and biomass content (fgure 4) was best described by a power function as smaller nests contained relatively less biomass. The majority of the biomass was composed of workers (roughly 75%) with the remaining part being brood and sexuals. The fnal model (fgure 5) produced estimates of ant biomass (table 1) with a 95% credibility interval of approxi- mately 75% of the estimated median value. Discussion and conclusion The combined biomass of the fve colonies in the plantation was 20 kg fresh wt ha -1 . For comparison, the amount of animal biomass in an Amazonian rainforest has been estimated to be about 200 kg ha -1 [4]. It is remarkable that a single ant species in a mango plantation can attain a biomass corresponding to 10% of the entire animal biomass in a rainforest. As opposed to destructive assessments, which are a snapshot of ant abun- dance, our method will allow a continuous assessment of O. smaragdina biomass dynamics. Thereby, laborato- ry measurements on physiological per capita rates can be scaled to ecosystem level: E.g the fow of nutrients from host tree to ants and vice versa can be estimated from per capita rates of ant carbohydrate consumption or waste product excretion. Hence, O. smaragdina can be utilised to assess the impact of ants in a tropical ecosystem, which at present is poorly understood.