The role of temperature in competition and persistence of an invaded ant assemblage

1. To achieve numerical dominance, an ectotherm consumer requires a sizeable abiotic window in which it can forage. Here we explore how one abiotic factor, temperature, provides opportunity and regulates the impact of the invasive red imported fire ant, Solenopsis invicta, on an urban ant assemblage. 2. We first quantified S. invicta's ability to outcompete native species by contrasting its foraging biomass to that of its potential competitors. In doing so, we found that S. invicta deployed more ant biomass at baits than the estimated whole colony biomass of three of the four co-occurring native species. It did so across c. 75% of the hours in a summer day, those hours below its thermal maximum of 49 degrees C. Higher thermal maxima allowed two native species to avoid encountering workers of S. invicta. 3. Exclosure experiments revealed that a third species, Dorymyrmex flavus, more similar in body size and thermal tolerance to S. invicta, was competitively suppressed by the invasive. Carbon and nitrogen stable isotope analysis suggests that D. flavus' persistence is likely due to dietary differences. 4. Although thermal and dietary traits help predict how species coexist in this invaded assemblage, one key to S. invicta's success is likely to be its ability to forage in all but 6 h of a summer's day.