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Thermal constraints on foraging of tropical canopy ants

  • Behavioral ecology – original research
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Small cursorial ectotherms risk overheating when foraging in the tropical forest canopy, where the surfaces of unshaded tree branches commonly exceed 50 °C. We quantified the heating and subsequent cooling rates of 11 common canopy ant species from Panama and tested the hypothesis that ant workers stop foraging at temperatures consistent with the prevention of overheating. We created hot experimental “sunflecks” on existing foraging trails of four ant species from different clades and spanning a broad range of body size, heating rate, and critical thermal maxima (CTmax). Different ant species exhibited very different heating rates in the lab, and these differences did not follow trends predicted by body size alone. Experiments with ant models showed that heating rates are strongly affected by color in addition to body size. Foraging workers of all species showed strong responses to heating and consistently abandoned focal sites between 36 and 44 °C. Atta colombica and Azteca trigona workers resumed foraging shortly after heat was removed, but Cephalotes atratus and Dolichoderus bispinosus workers continued to avoid the heated patch even after >5 min of cooling. Large foraging ants (C. atratus) responded slowly to developing thermal extremes, whereas small ants (A. trigona) evacuated sunflecks relatively quickly, and at lower estimated body temperatures than when revisiting previously heated patches. The results of this study provide the first field-based insight into how foraging ants respond behaviorally to the heterogeneous thermal landscape of the tropical forest canopy.

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We thank Oris Acevedo, Belkys Jimenez, and the staff of the Smithsonian Tropical Research Institute for logistical support in Panama. Amanda Winters assisted in the field. Comments from Jelena Bujan, Walter Carson, James Lichtenstein, and two anonymous reviewers improved the manuscript.

Author contribution statement

SPY, AYS, and BJA conceived and designed the experiments. MES, BJA, and AYS performed the experiments. SPY, MES, BJA, RK, and AYS analyzed the data. MK provided editorial advice, and all authors contributed to writing the manuscript.


This research was supported by National Science Foundation Grants DEB-1252614 to SPY, and DEB-0842038 and EF-1065844 to MK.

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Correspondence to Stephen P. Yanoviak.

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The authors declare that they have no conflict of interest.

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This article does not contain any studies with human participants or vertebrate animals performed by any of the authors.

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Communicated by Raphael Didham.

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Spicer, M.E., Stark, A.Y., Adams, B.J. et al. Thermal constraints on foraging of tropical canopy ants. Oecologia 183, 1007–1017 (2017).

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