The outcome of interspecific competition is determined within the first 15 minutes of interaction

Background/Question/Methods

There is a known trade-off between resource competition abilities and dominancy in ant foraging behavior. This trade-off is believed to be part of the factors maintaining species coexistence. Most ant species excel in one component on the expense of the other. We asked how long it takes to resolve dominancy conflicts over food. In addition, we asked how would natural foraging dynamics change with the introduction of an invasive species? We hypothesized that the intruder would take over the local resources more efficiently than the native species. We compared the foraging dynamics of ants in two natural sites and two near-by semi-natural sites, with a similar habitat, but located close to buildings. Previously, we found that ant communities differed strongly between these habitats. While 11 native ant species were found in the natural sites, semi-natural sites only supported two species, the native winter ant (Prenolepis imparis), and the invasive Argentine ant (Linepithema humile). On this study, we monitored ant presence at food baits during three time intervals – 15, 60, and 120 minutes after setting the baits. We observed a total of 432 baits, three times each, counting the number of individuals and identifying the species. 

Results/Conclusions

Interestingly, when examining ant species dynamics at baits, we’ve found that species presence did not change significantly between observations. The species composition at baits within 15 minutes of setting the baits was almost identical to the species composition 45 and 105 minutes later. Therefore, bait discovery is very quick in these ant communities, and whoever is the first to discover baits, would probably dominate them. In addition, most species would rarely lose a bait. The Argentine ant got the highest score on every measured parameter compared with other ant species observed in the current study. It was the first to locate baits, it recruited the highest number of workers, and it spent the longest time at baits. In overall, it got the highest “ant-hour” index, giving it a great advantage over the native species in acquiring food resources. The Argentine ant’s superior foraging abilities are probably part of the factors that enables this species to outcompete and displace most of the native species it encounter in its invasive range.