Wood ants and their interaction with other organisms

Abstract

Wood ants ( Formica rufa group) interact with a wide range of other organisms at multi-trophic levels. Chapter 6 discusses competitive interactions between wood ants and other ant species, and Chapter 7 explores the fundamental mutualistic interaction between wood ants and aphids. This chapter takes a wider approach still, to explore the effects of wood ants on invertebrate communities on the forest floor and in tree canopies, including their potential impact on invertebrate pests. The multiple mechanisms by which other invertebrates (myrmecophiles) infiltrate and survive in and around ant nests without being harmed are reviewed. Finally, consideration is given to how wood ants affect more distant taxa such as the vegetation surrounding their nests, the trees on which they forage and woodland vertebrates. Aboveground interactions The main effects of wood ants on tree-crown invertebrates The key trophic effects of wood ants are predation of invertebrates and mutualism with aphids (see Chapter 7). These interactions have a considerable influence in shaping the communities of tree-crown invertebrates (Figure 8.1). The ants generally reduce the overall abundance of non-tended aphids and invertebrates of all trophic groups and taxa. In contrast, ant-tended aphid species usually increase in abundance (Warrington and Whittaker 1985a, b; Mahdi and Whittaker 1993; Wimp and Whitham 2001; Punttila et al . 2004). The wood ants both protect their tended aphids and use them as prey items (Billick et al . 2007). Temporary shifts from mutualistic to predatory behaviour may occur when there is a surplus of aphids (Way 1963; Sudd and Franks 1987) and a lack of other abundant prey items, or the ants may target injured, dead or immobile (e.g. moulting) aphids or those producing honeydew of poor quality or quantity (Sakata 1994; see Chapter 7). The wood ants protect their mutualistic species of aphids by removal of other predatory, parasitic and hyperparasitic invertebrates (Liere and Perfect 2008) and the aphids’ competitors, such as non-ant-tended aphid species and other herbivores (Novgorodova 2005; Billick et al . 2007), which can form a large part of the ants’ prey (Punttila et al . 2004). This helps to secure the ants’ supply of carbohydrate, which they gather from the aphids in the form of honeydew (Mooney and Mandal 2010).