More food, less habitat: how necromass and leaf litter decomposition combine to regulate a litter ant community

Abstract

1. In brown food webs of the forest floor, necromass (e.g. insect carcasses and frass) falling from the canopy feeds both microbes and ants, with the former decomposing the homes of the latter. In a tropical litter ant community, we added necromass to 1 m2 plots, testing if it added as a net food (increasing ant colony growth and recruitment) or destroyer of habitat (by decomposing leaf litter).2. Maximum, but not mean, colony growth rates were higher on +food plots. However, neither average colony size, nor density was higher on +food plots. In contrast, +food plots saw diminished availability of leaf litter and higher microbial decomposition of cellulose, a main component of the organic substrate that comprises litter habitat.3. Furthermore, necromass acted as a limiting resource to the ant community only when nest sites were supplemented on +food plots in a second experiment. Many of these +food +nest plots were colonised by the weedy species Wasmannia auropunctata.4. Combined, these results support the more food–less habitat hypothesis and highlight the importance of embedding studies of litter ant ecology within broader decomposer food web dynamics.