Study of Iconic Native and Invasive Florida Ant Species

With the rapid transport of plants, produce, and goods out of its South American home, the fire ant, Solenopsis invicta, has invaded continents on a global scale. In the United States alone, S. invicta is responsible for an estimated $1 billion in damages annually. In contrast to the invasive fire ant, Florida’s native harvester ant, Pogonomyrmex badius, is a keystone seed disperser, providing seed relocation benefits to Florida’s sandhill wildfire-adapted habitats. Seed relocation reduces seedling competition for nutrients with the parent plant, reduces predation of seeds by rodents, increases nutrient loads associated with ant mound soils, and protects seeds from natural disasters. In short, P. badius is a desert ant adapted to dryer wildfire habitats. In contrast, S. invicta is a swamp ant adapted to wetter grassy habitats with seasonal floods. In this study of these two iconic Florida ant species, I explored the mortality of workers when exposed to extreme weather events. I simulated wildfires using a smoker, cold snaps using a refrigerator at 0.5oC, heat waves using a dry oven at 45.5oC, and floods using open containers of water. I tested three hypotheses: (H1) Larger ants are “less” likely to perish when exposed to temperature extremes in heat, flooding, and cold trials (Bergmann’s Rule; Gigantothermy). (H2) Larger ants are “more” likely to perish in smoke trials because they retain a greater portion of particulate matter (Kmoch et al. 1976). (H3) Ants in larger groups are “less” likely to perish when exposed to temperature extremes in heat, smoke, flooding, cold, and humidity trials (Koto et al. 2015). The percent mortality for P. badius workers did not differ from the control for cold, smoke, and flooding. Morality during the heat treatment was 17%. Across treatments, smaller worker sizes and isolated workers were significant predictors of mortality. The percent mortality for S. invicta was between 30% and 80% across the four treatments. Smaller worker size, but not group size, was a significant predictor of mortality. However, because P. badius workers averaged 12 times the mass of S. invicta, the harvester ant survived at a rate averaging 10 times that of S. invicta workers. In the remaining sections of this thesis, I expand on each study species, their conservation value, theories related to the surface-area-to-volume ratio of animals (i.e. body size), the natural history of each ant species, and my study hypotheses. Finally, I discuss the implications of this study in light of expanding anthropogenic habitat encroachment and climate change.