Online

Miller, Katie Ann

Biology

2018

M.S.

Climate change is predicted to impact organismal nutritional ecology. Increased temperatures can directly accelerate physiological rate processes, which in turn, impact nutritional requirements. Climate change can also impact organisms indirectly by altering the quality and quantity of nutritional resources, creating the potential for nutritional mismatch between what nutrients are available in the environment and what organisms require. Investigation of organismal stoichiometry, particularly the balance of carbon, nitrogen, and phosphorus content of organisms, can help illuminate the extent to which changes in climate may impact organism nutritional ecology. Ants represent an excellent system to examine stoichiometry because they occur across a broad range of environmental conditions and perform important ecosystem services, such as seed dispersal, which may impact ecosystem functioning. In this thesis, I examined how climate variables influence ant stoichiometry across a broad latitudinal gradient in natural populations of three closely-related ant species in the genus Aphaenogaster. In a common garden study, I tested the extent to which such stoichiometric variation was due to plastic or evolved variation. I found significant species-specific differences in how ant stoichiometry responded to climate gradients. The northern species, A. picea contained more C, and less N and P at higher latitudes and elevation, consistent with increased winter lipid storage. In contrast, the more southern species, A. rudis, showed the opposite pattern, which may reflect N and P limitation at southern extremes. Aphaenogaster fulva, whose range is intermediate in latitude and partially overlaps with both congeners, contained more C in environments with more seasonal precipitation. Thus, these species appear to use different nutrient storage strategies in response to the variation in abiotic and trophic conditions across their range. When reared under the same feeding regime and thermal conditions, site-level differences in nitrogen storage between a northern and a southern ant population were retained over time and across years, suggesting that adaptive divergence in elemental composition is at least partially responsible for clinal patterns in the field. To connect latitudinal patterns to temporal changes projected under climate change, I evaluated how increases in temperature impact ant stoichiometry and associated functional traits at the individual and colony level using an experimental field mesocosm experiment at two sites, Harvard Forest (HF) and Duke Forest (DF). I examined how experimental increases in temperature impacted ant body size, colony demography, and nutritional status of two Aphaenogaster ant species. I found that Aphaenogaster ants at the northern site, HF, responded positively to direct increases in temperature, with increases in colony biomass, colony size, total reproductive output, and shifts toward increased nitrogen content with increases in temperature. In contrast, Aphaenogaster ants at the southern site, DF, were generally unaffected by temperature except for a decrease in maximum colony size with increases in temperature. Together, my findings provide evidence that both climate variables and evolutionary history impacts ant stoichiometry, which in turn, may impact ant colony fitness. Examination of the biochemical basis of stoichiometric trait variation is needed to ascertain the role stoichiometry may play in how ant species adapt to changing environmental conditions.