Can behaviour and physiology mitigate effects of warming on ectotherms? A test in urban ants

• Published in: The Journal of animal ecology Vol. 92; no. 3; pp. 568 - 579
• Main Authors: Youngsteadt, Elsa, Prado, Sara Guiti, Keleher, Kirsten Joanna, Kirchner, Michelle
• Format: Journal Article
• Language: English
• Published: England Blackwell Publishing Ltd 01.03.2023
• Subjects: Activity patterns; air; Air temperature; animal ecology; Animals; Ants; Ants - physiology; Baits; behavioural thermoregulation; Body temperature; climate; Climate Change; CTmax; Diel activity; ectothermy; Environmental effects; forest habitats; Formicidae; Geographical distribution; Global climate; Global warming; heat tolerance; Hot Temperature; Insecta; Insects; Microclimate; North Carolina; Physiological effects; Physiology; Seasonal variations; Species; Species diversity; summer; Temperate forests; Temperature; Temperature tolerance; thermal limits; thermal preference; Thermal stress; Thermoregulation; Urban forests; North Carolina; heat tolerance; Formicidae; thermal preference; CTmax; behavioural thermoregulation; thermal limits
• ISSN: 0021-8790; 1365-2656; 1365-2656
• DOI: 10.1111/1365-2656.13860

Global climate change is expected to have pervasive effects on the diversity and distribution of species, particularly ectotherms whose body temperatures depend on environmental temperatures. However, these impacts remain difficult to predict, in part because ectotherms may adapt or acclimate to novel conditions or may use behavioural thermoregulation to reduce their exposure to stressful microclimates. Here we examine the potential for physiological and behavioural changes to mitigate effects of environmental warming on five species of ants in a temperate forest habitat subject to urban warming. We worked in eight urban and eight non‐urban forest sites in North Carolina, USA; sites experienced a 1.1°C range of mean summer air temperatures. At each site, we documented species‐specific microclimates (ant operative temperatures, Te) and ant activity on a transect of 14 bait stations at three times of day. In the laboratory, we measured upper thermal tolerance (CTmax) and thermal preference (Tpref) for each focal species. We then asked whether thermal traits shifted at hotter sites, and whether ants avoided non‐preferred microclimates in the field. CTmax and Tpref did not increase at warmer sites, indicating that these populations did not adapt or acclimate to urban warming. Consistent with behavioural thermoregulation, four of the five species were less likely to occupy baits where Te departed from Tpref. Apparent thermoregulation resulted from fixed diel activity patterns that helped ants avoid the most inappropriate temperatures but did not compensate for daily or spatial temperature variation: Hotter sites had hotter ants. This study uses a novel approach to detect behavioural thermoregulation and sublethal warming in foraging insects. The results suggest that adaptation and behaviour may not protect common temperate forest ants from a warming climate, and highlight the need to evaluate effects of chronic, sublethal warming on small ectotherms. This study combines laboratory and field assays to detect behavioural thermoregulation in foraging ants. Despite some thermoregulation, the results suggest that neither adaptation nor behaviour will protect common temperate forest ants from climate change and highlight the need to evaluate effects of chronic, sublethal warming on small ectotherms.