The Argentine ant (Linepithema humile), from humble beginnings in South America, is now invasive on every continent and has a place on the list of 100 of the World’s Worst Invasive Alien Species. Transported around the world via human activity, this omnivorous ant impacts upon native flora and fauna and has been incredibly successful in outcompeting and displacing native ants. A recent study indicates, however, that at least one species may be ready to make a stand against the onslaught of the Argentine ant.
An Argentine ant queen and worker (Source: Alex Wild)
The Argentine ant (Linepithema humile) is notorious in the world of invasion biology not only for its ability to invade a wide range of habitats (both sub-tropical and temperate) and displace native species, but also for its tendency to form “supercolonies” – the precise definition of which is a muddy area (see Myrmecos) – but which may span hundreds or thousands of kilometres, with populations of ants of the same supercolony interacting non-aggressively with one another. Only last year an intercontinental “megacolony” of Argentine ants was reported, comprised of inter-related supercolonies from Europe, Japan and America. It is not strictly evident that the supercolonial life history of Argentine ants is the key to their invasion success, though this is a widely supported theory. What is fact, however, is that the Argentine ant has displaced well established native ant populations around the world, leading to a variety of possible effects from reduced arthropod diversity through increased predation, to fears of a reduction in plant biodiversity brought about by reduced insect-plant interactions such as seed dispersal, normally carried out by native ants.
There is currently no effective specific method of control to limit the impact and spread of the Argentine ant. A recent paper by Blight et al. (2010), however, provides encouraging evidence that L. humile may face tough competition from native ants in at least some of its introduced range. Blight et al. report that on the French Mediterranean island of Corsica, the locally dominant native ant species, Tapinoma nigerrimum, may be responsible for limiting the Argentine ant invasion. The team carried out assays, studying interspecific interactions between the ants as well as performance and outcomes when the two species competed for food and space. The results suggest that whilst Argentine ants can compete with T. nigerrimum by “initiating more fights, using cooperation and simultaneously deploying physical and chemical defenses”, the native ant was more efficient in both interference and exploitative competition, dominating in food and space competition assays and going on to invade Argentine ant nests, the reverse of which was never observed. The results of this study offer hope that native ants may limit the extent and success of L. humile invasions, potentially preventing the Argentine ants’ establishment, eliminating nests and inhibiting the formation of supercolonies.
As Blight et al. conclude, on a broader ecological scale the results of this study display that interspecific competition from an established dominant native species may impact upon the success of invading species, in this instance by reducing the likelihood of incipient colony establishment and survival.
Invasive Species Research Scientist
Blight, O., Provost, E., Renucci, M., Tirard, A. & Orgeas, J. (2010) A native ant armed to limit the spread of the Argentine ant. Biological Invasions. 12: 3785-3793.
Rowles, A.D. & O’Dowd, D.J. (2007) Interference competition by Argentine ants displaces native ants: implications for biotic resistance to invasion. Biological Invasions. 9: 73-85.
Walters, A.C. & Mackay, D.A. (2005) Importance of large colony size for successful invasion by Argentine ants (Hymenoptera: Formicidae): Evidence for biotic resistance by native ants. Austral Ecology. 30: 395-406.