Costs and benefits for phytophagous myrmecophiles: when ants are not always available

Costs and benefits in mutualistic associations between ants and phytophagou s myrmecophiles are context dependent. We collected information from the li terature on costs and benefits of myrmecophily in aphids, coccids, membraci ds and lycaenids. A key result of the literature survey is that investment in mutualism with ants entails costs paid not only when ants are present (d irect costs) but also when they are absent (indirect costs). We incorporate d such a trade-off in a model that investigates the fitness consequences of the decision of a potential myrmecophile whether or not to invest in coope ration with ants. The model shows that whether myrmecophily should be favou red depends on the rate of increase of the population, and, if there are in direct costs, on the frequency of habitats with ants. Both direct and indir ect costs can limit or prevent the evolution of myrmecophily even when ants are abundant. To understand the patterns of associations in the field we t herefore need to measure the benefits and costs of myrmecophily both in the presence and in the absence of ants.