Canopy ants are out in the cold in temperate forests

Abstract

Research Highlight: Kirchner, Michelle; Sorenson, Clyde; Youngsteadt, Elsa (2025). Too cold to handle: Climatic constraints on arboreal ants in temperate forests. Journal of Animal Ecology. Ants are among the most abundant animals on the planet and they have a huge impact of ecosystems worldwide. Being small-bodied ectotherms, their growth, survival and reproduction is closely tied to the temperatures they experience (the microclimate), and hence the thermal physiology of different ant species determines their global and regional distribution and is subject to change under climate warming. Forest habitats present a significant additional climate gradient from ground to canopy, and its implications for tropical ant species have been reasonably well explored. Yet these findings cannot easily be easily applied to temperate forests, where seasonal variation in temperature and vegetation could mean very different things for ant communities. Kirchner, Sorenson, & Youngsteadt (2025) address this research gap by measuring the thermal tolerance of ants collected from the ground and canopy, across seasons, and alongside measurements of air and nest temperatures. As elsewhere, ants that experience a broader range of temperatures—in this case, canopy ants—have a broader thermal tolerance than those experiencing more stable temperatures—the ground-dwelling ants. Ants from both strata adapted their cold tolerance to cope with winter cold, while heat tolerance did not change, in line with previous evidence that heat tolerance is a less labile trait. Perplexingly, however, canopy ants were less tolerant of winter cold despite being far more exposed to extreme cold. Thus, this paper provides an intriguing insight into how ecophysiological rules play out for ants across the vertical gradient of temperate forests, suggesting that canopy ants here are more limited by tolerance of winter cold. This could suggest that the diversity of temperate forest canopies may increase as winters become less extreme, which could have important implications for temperate forest ecosystems.