Thermal traits predict the winners and losers under climate change: an example from North American ant communities

Authors: Roeder, Karl; BUJAN, JELENA - University Of Lausanne; DE BEURS, KIRSTEN - University Of Oklahoma; WEISER, MICHAEL - University Of Oklahoma; KASPARI, MICHAEL - University Of Oklahoma

Submitted to: Ecosphere
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/8/2021
Publication Date: 7/2/2021
Citation: Roeder, K.A., Bujan, J., De Beurs, K., Weiser, M., Kaspari, M. 2021. Thermal traits predict the winners and losers under climate change: an example from North American ant communities. Ecosphere. 12(7). Article e03645. https://doi.org/10.1002/ecs2.3645.
DOI: https://doi.org/10.1002/ecs2.3645

Interpretive Summary: Current temperatures are predicted to increase with consequences for many taxonomic groups. Ectotherms, whose body temperature tracks the environment, may be particularly at risk. From warm deserts to cold tundra, we documented how 33 ant communities across North America have changed over 20 years to test predictions from thermal performance theory that ant genera with higher thermal limits have increased at the expense of less thermally tolerant groups. Consistent with our predictions, we found a positive relationship between CTmax, the temperature at which muscle control is lost, and the proportion of sites in which an ant genus’ incidence had increased. However, this was not the case for CTmin, the low temperatures at which ants first become inactive. We suggest additional working hypotheses for why particular genera have increased, decreased, or remained constant through time and why mean annual temperatures and evolutionary history explained little of this pattern. Combined, we suggest functional traits like CTmax are useful for predicting how this ecologically important insect taxon has changed and will continue to change in the near future.

Technical Abstract: Across the globe, temperatures are predicted to increase with consequences for many taxonomic groups. Arthropods are particularly at risk as temperature imposes physiological constraints on growth, survival and reproduction. Given that arthropods may be disproportionately affected in a warmer climate—the question becomes which taxa are vulnerable and can we predict the supposed winners and losers of climate change? To address this question, we resurveyed 33 ant communities, quantifying 20-year differences in the incidence of 28 genera. Each North American ant community was surveyed with 30 1-m2 plots, and the incidence of each genus across the 30 plots was used to estimate change. From the original surveys in 1994-1997 to the resurveys in 2016-2017, temperature increased on average 1°C (Range: -0.4°C to 2.5°C) and ca. 64% of ant genera increased in more than half of the sampled communities. To test Thermal Performance Theory’s prediction that genera with higher average thermal limits will tend to accumulate at the expense of those with lower limits, we quantified critical thermal maxima (CTmax: the high temperatures at which they lose muscle control) and minima (CTmin: the low temperatures at which ants first become inactive) for common genera at each site. Consistent with prediction, we found a positive decelerating relationship between CTmax and the proportion of sites in which a genus had increased. CTmin, by contrast, was not a useful predictor of change. There was a strong positive correlation (r = 0.85) between the proportion of sites where a genus was found with higher incidence after 20 years and the average difference in number of plots occupied per site, suggesting genera with high CTmax values tended to occupy more plots at more sites after 20 years. Thermal functional traits like CTmax have thus proved useful in predicting patterns of long-term community change in a dominant, diverse insect taxon.