Quantification of Ant Manure Deposition in a Tropical Agroecosystem: Implications for Host Plant Nitrogen Acquisition

Abstract

Ants are functionally important organisms in most terrestrial ecosystems. Being ubiquitous and abundant, ant communities can affect the availability of resources to both primary and secondary consumers. As nitrogen is a limiting nutrient for plant growth in most terrestrial ecosystems, deposition of ant manure may augment the host plants’ acquisition of nitrogen. In this study, we quantified the manure deposited by colonies of the Asian weaver ant Oecophylla smaragdina. We developed a method to estimate the amount of manure deposited in host trees (Mangifera indica) based on the trail activity of O. smaragdina. The rate of manure deposition was on average 62.3 kg dw ha−1 y−1, of which 0.2 kg ha−1 y−1 was deposited as urea-N, a nutrient that may be absorbed directly through the leaves, and 1.9 kg ha−1 y−1 was deposited as total nitrogen. Furthermore, ants given access to sucrose solution increased their rate of manure deposition significantly, suggesting that nectaries and/or trophobionts may play a major role in the production of ant manure. This study reveals that O. smaragdina can supply a significant amount of nitrogen to their host plants. In light of their remarkable abundance, the manure deposition by ants may have a hitherto unappreciated impact on the allocation of nutrients within their ecosystem.