Background:
By increasing the mean and variance of environmental temperatures, climate change has caused local extinctions and range shifts that are likely to intensify over time. Previously, biologists projected impacts of climate change from the acute heat tolerances of adult organisms; however, this approach ignores important factors, such as the cumulative damage from heat exposure and the variation in heat tolerance among individuals in different physical conditions and at different life stages. Biologists have been challenged by the need to predict the persistence of populations and species during climate change. Although the earliest predictions relied on correlations between environmental variables and species occurrences, Deutsch et al. (2008) pioneered a mechanistic approach, in which vulnerability was inferred from physiological traits such as heat tolerance. However, predicted vulnerability depends strongly on one's assumptions about thermal sensitivity and environmental temperature. One common approach is to infer vulnerability to climate change from projected changes in monthly air temperatures, but these macroclimatic data do not capture the variation in temperature experienced by most organisms. Climate change will further amplify this thermal variation by increasing the magnitude, duration and frequency of extreme weather events such as heat waves. Because heat waves can abruptly kill many organisms, greater thermal variability poses a major threat to biodiversity.
Methods:
We measured the effects of hydration state and life stage on the heat tolerance of an agricultural pest, the South American locust (Schistocerca cancellata). By measuring tolerance time across a range of temperatures, we estimated tolerance of both chronic and acute exposures to high temperatures. We then used these data to model the injury and survival of locusts in microclimates of the past (1961–1990), present (1991–2020) and future (uniform warming of 3°C).
Results:
Locusts succumbed to heat stress exponentially faster as temperature increased, but hydration state and life stage altered this exponential relationship.
Data Summary:
Our modelling indicated that recent climate change has amplified the risk of overheating, with predicted injury and survival depending strongly on a locust's access to shade and water. The provided text does not contain specific quantitative statistics (e.g., exact tolerance times or statistical values); the reported findings are qualitative descriptions of exponential relationships and modeled outcomes.
Conclusions:
If changes in climate and land use reduce the availability of these resources (shade and water), locust populations may shift their geographic range faster than currently predicted. To accurately predict range shifts and associated crop losses, mechanistic models of locust distributions should consider the combined stressors of heat and dehydration.
Practical Significance:
Because the South American locust is an agricultural pest, understanding how dehydration and heat stress affect its survival is critical for predicting crop losses and geographic range shifts under climate change. Mechanistic models that incorporate these combined stressors can improve forecasts of locust outbreaks and inform management strategies.