Foraging behavior and seed dispersal mutualisms in a warmed world: The effects of experimental warming on ant assemblages and the processes they mediate

Background/Question/Methods

Climatic warming alters the composition of communities and mediates interspecific interactions. In this study, we explored the effects of climatic warming on ant assemblages as well as the processes they mediate. In 12 open-top chambers at Duke Forest and 12 more at Harvard Forest, we have continuously increased air temperatures in ~ 0.5 ºC steps up to 5.5 ºC above ambient conditions. In 2010 and 2011, we focused on the foraging activity of ant species across the range of warming treatments and examined the broader impact of warming on the system by examining rates of ant-mediated seed dispersal. We predicted that warming would alter foraging activity across all species, but that responses would vary between sites and among species. Further, we predicted that any changes in foraging activity would ultimately alter rates of seed dispersal. 

Results/Conclusions

The effects of experimental warming on foraging activity varied dramatically among species. These impacts were not surprising based on the thermal physiology of the species: species with higher thermal tolerances, such as Crematogaster lineolata and Aphaenogaster lamellidens, exhibited higher activity levels under warmed conditions than did species with lower critical thermal maxima, such as Prenolepis imparis. Additionally, foraging activity was 2.4 × higher in the hottest chambers as compared to ambient chambers at the southern site (F = 5.72, p = 0.02, R² = 0.58), while temperature and foraging activity were unrelated at the northern site (F = 0.16, p = 0.70, R² = 0.31). Surprisingly, these changes in foraging activity did not drive changes in seed dispersal rates, either overall (F = 1.34, p = 0.43, R² = 0.08), or by particular ant species. Approximately 25% of seeds were removed from experimental seed caches within an hour, across sites and temperature treatments. This may suggest that the idiosyncratic responses of species to warming may cancel each other out, perhaps enhancing the resilience of seed dispersal mutualisms to warming.