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Harvard Forest REU Symposium Abstract 2012

  • Title: Hot Ants: An Exoploration of Ant Nests and Temperature Change
  • Author: Matthew A Combs (Hamilton College)
  • Abstract:

    The ant Formica subsericea is a widespread and abundant species, known to drive ecosystem function through soil turnover, seed dispersal, and nitrogen movement. While these above-ground activities are well documented and fairly easy to observe, little is known about the way F. subsericea colonies behave within their subterranean nests. I describe the distribution of adult ants and their brood in F. subsericea nests and determine whether they are significantly affected by the soil temperature as it shifts throughout the day. At a field site in Montague, Massachusetts I extracted nine nest casts by pouring molten wax down the surface entrances at particular times of the day, essentially freezing them in time. The casts were excavating once the wax solidified. In the laboratory these nests were weighed, photographed, and melted down, providing accurate counts of adults ants and various stages of brood development at known depths. A bimodal trend was recorded for the distribution of nest volume as described by depth, with a large peak around 15cm and a minor peak around 30cm. Similar patterns were found to exist in the distribution of both ants as well as brood in the early morning hours, when temperatures are cooler. During the hottest hours of the day, the bimodal trend was absent. These ants and brood were found at deeper temperatures, with very few remaining above 15cm in depth. Temperature gradients from the field site show that below 15cm temperatures become fairly steady at 25°C. Between 0 and 15cm, temperatures are known to change upwards of 20°C throughout the day. These results support previous conclusions that some ant species move their brood throughout the day in order to optimize temperature for brood development (Roces, 1989). We can now say that the ideal temperature for F. subsericea is about 25°C. These results also mean that further temperature increases, as predicted by global climate change models, would drive the ants deeper in order to reach the same optimum temperature. This would mean more colony energy would be spent on digging and brood movement, leaving less colony energy for above-ground activities and a potential loss of ecosystem fitness. More research into energy allocation and brood development is required to be certain of these claims.

  • Research Category: Large Experiments and Permanent Plot Studies