Interactions between the ants Linepithema humile, Tapinoma sessile and aphid mutualists

Abstract

Invasive species have major impacts on the ecosystems they invade. Among the most disruptive groups of invasive species are ants. Invasive ants have caused losses in biodiversity among a wide range of taxa, including birds, mammals, lizards, but especially towards ground nesting arthropods such as native ants. Why native ants are so susceptible to invasion and how invasive ants are able to sustain massive population growth remain unclear. It has been suggested that invasive ants utilize carbohydrate resources from hemipteran exudates to fuel aggressive foraging and colony expansion. Perhaps invasive ants are simply more proficient at usurping these resources, maintaining higher hemipteran populations, etc. Our work uses a model invasive, the Argentine ant, , Linepithema humile, and a native ant Tapinoma sessile to quantify hemipteran tending ability and competition. Through a series of laboratory and field experiments we were able to quantify 1) carbohydrate sequestering performance, 2) the effect either ant species had on hemipteran population growth rates in a predator-free space, 3) the defense ability of either ant against hemipteran predators and parasitoids, and 4) the proportion of invasive ants required to displace a native colony from a hemipteran resource. Neither ant demonstrated a better ability to sequester liquid resources; however recruitment strategies were much different. Hemipteran populations in the presence of L. humile grew larger in a predator free environment and populations exposed to predators were better defended by L. humile than T. sessile. L. humile was able to displace T. sessile from a nest site without having a majority of worker ants. Aggression of either ant species was significantly reduced without hemipterans present. Understanding factors that drive invasive species can give us insight into native areas that may be susceptible for invasion, how potential mutualist populations might respond and possibly provide us with an avenue for secondary control measures given the economic and ecological importance of invasive species.