title: Thermal constraints on foraging of tropical canopy ants.
abstract: 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.
authors.affiliation: Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA, 15260, USA.
authors.forename: Michelle Elise
authors.initials: ME
authors.lastname: Spicer
authors.affiliation: Department of Biology, University of Louisville, Louisville, KY, 40292, USA.
authors.forename: Alyssa Y
authors.initials: AY
authors.lastname: Stark
authors.affiliation: Department of Biology, University of Louisville, Louisville, KY, 40292, USA.
authors.forename: Benjamin J
authors.initials: BJ
authors.lastname: Adams
authors.affiliation: Department of Biology, University of Louisville, Louisville, KY, 40292, USA.
authors.forename: Riley
authors.initials: R
authors.lastname: Kneale
authors.affiliation: Department of Biology, University of Oklahoma, Norman, OK, 73019, USA.|Smithsonian Tropical Research Institute, Balboa, Republic of Panama.
authors.forename: Michael
authors.initials: M
authors.lastname: Kaspari
authors.affiliation: Department of Biology, University of Louisville, Louisville, KY, 40292, USA. steve.yanoviak@louisville.edu.|Smithsonian Tropical Research Institute, Balboa, Republic of Panama. steve.yanoviak@louisville.edu.
authors.forename: Stephen P
authors.identifier: 0000-0001-6425-1413
authors.initials: SP
authors.lastname: Yanoviak
mesh_terms: D000818:Animals; D001000:Ants; D005247:Feeding Behavior; D065928:Forests; D006358:Hot Temperature; D013696:Temperature; D014197:Trees
keywords: Arboreal; Behavior; Formicidae; Panama; Sunfleck