Thermal tolerance regulates foraging behavior of ants

Authors: ROEDER, DIANE - South Dakota State University; PARASKEVOPOULOS, ANNA - University Of Colorado; Roeder, Karl

Submitted to: Ecological Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/23/2021
Publication Date: 1/17/2022
Citation: Roeder, D.V., Paraskevopoulos, A.W., Roeder, K.A. 2022. Thermal tolerance regulates foraging behavior of ants. Ecological Entomology. 47(3):331-338. https://doi.org/10.1111/een.13118.
DOI: https://doi.org/10.1111/een.13118

Interpretive Summary: How does temperature affect the behavior of animals? We used an abundant harvester ant species, Pogonomyrmex barbatus, to address this question in the mixed grass prairies of south-western Oklahoma. We specifically focused on foraging behavior and over two years tracked 322 foraging trips from 15 colonies. During each trip, we measured surface temperature, distance, time, worker mass, seed mass, and foraging tempo (i.e. running speed). We also quantified the thermal tolerance of ants to determine if temperature was a physiological constraint on foraging. Our results suggest that time, but not distance, decreased with increasing temperature, resulting in an increased foraging tempo as ants neared their thermal tolerance of 50°C. Worker size and seed size were unrelated to temperature. Combined, our results highlight how variation in temperature can directly affect behavior by not only limiting foraging but also by increasing foraging rates near an ant’s thermal limit.

Technical Abstract: Using a central place forager, we test predictions about how daily temperature fluctuations and thermal tolerance measurements combine to influence foraging in the red harvester ant, Pogonomyrmex barbatus. Over two years, we tracked 322 foraging trips from 15 colonies in a mixed grass prairie of south-western Oklahoma. During each trip, we measured surface temperature, distance, time, worker mass, seed mass, and foraging tempo (i.e. running speed). To assess P. barbatus heat tolerance, we measured CTmax and knock-down resistance of field-collected workers in the lab. Trip time, but not distance, decreased with increasing temperature, resulting in an increased foraging tempo as ants neared their CTmax of 50°C. Knock-down resistance trials confirmed that 50°C is an upper thermal limit, as individuals showed decreasing survival from 100% at 45°C to 0% at 50°C. Worker size and collected seed size were unrelated to temperature. Our results highlight how daily temperature fluctuations drive activity, not only by limiting foraging but also by increasing foraging rates near the thermal limit. If temperatures continue to increase, the foraging ability of this and similar species may be restricted to an ever-narrowing window with effects potentially extending to the surrounding community.