John Ludka (MS 2008) studied interactions between ants and the coast barrel cactus, which produces extra-floral nectar attractive to ants. The ants in turn protect cacti from insect herbivores. More than twenty ant species protect cacti but nearly all disappear following invasion by the Argentine Ant. Over the spring and summer, cacti vary in the diversity of ant bodyguards present, with cacti in invaded areas supporting the fewest ant species. For individual cacti, seed size increases with the number of ant species present apparently because cacti visited by multiple ant species receive more consistent protection over time. Ant diversity may thus act as insurance in the maintenance of this mutualism.
Ludka, J and DA Holway. Ant diversity acts as insurance in the maintenance of a protection mutualism with the coast barrel cactus. In preparation.
LeVan, KE, KJ Hung, KR McCann, J Ludka and DA Holway. (2014) Floral visitation by the Argentine ant reduces pollinator visitation and seed set in the coast barrel cactus, Ferocactus viridescens. Oecologia.174: 163–171.