Ant Community Dynamics and the Effects of Global Warming

This dissertation seeks to provide an understanding of how species coexist and, further, how climate change may alter communities by acting on the mechanisms that promote coexistence. Specifically, I examined coexistence among ant species in eastern deciduous forests and the effects that warming may have on foraging activity. Through a series of field observations, I sought evidence for the importance of four of the most commonly cited mechanisms for coexistence among ant species: the dominance – discovery tradeoff, the dominance – thermal tolerance tradeoff, spatial segregation, and niche partitioning. In this system, I did not find evidence for any of these mechanisms, but did find evidence that ant species were segregating the time of day during which they forage. Through an experimental temperature manipulation, I examined the potential effects of climatic warming on ant foraging behavior. I found warming to alter overall rates of foraging, as well as species-specific rates. The relative effects of temperature on foraging rates were predictable based on the thermal tolerance of the species. Finally, I examined the potential for these altered levels of foraging to cause shifts in rates of ant-mediated seed dispersal, providing an indirect mechanisms via which climatic warming may alter the plant community. Despite the observed shifts in ant activity, however, I did not find rates of seed dispersal to vary across temperature treatments. In sum, this dissertation suggests that the mechanisms promoting coexistence among ant species are complex and likely differ from place to place, but that segregation of foraging times may be important in some cases. Additionally, climate change is likely to affect ant communities by altering foraging behavior variably across species, but this may not have direct consequences for the plant community as a result of shifts in rates of seed dispersal.