The effects of global warming are often assessed as long-term impacts on species or population distributions. For individuals, especially among ectotherm ("cold-blooded") organisms, however, fatal heat failure may occur during heatwaves or even diurnal temperature extremes.
This study explores the thermal sensitivities of ectotherms at the level of biological processes of growth, homeostatis, and ageing. While these remain modest in the "permissive" temperature range associated with life, they become extraordinarily sensitive in the stressful temperature range with fatal consequences.
By analysing the effects of temperature on the rates of biological processes in data compiled for 314 ectotherm species, they showed that thermal sensitivities mirror those of enzyme catalytic rates, feeding and metabolism, increasing fitness with temperature by seven per cent per degree. At the breaking point between permissive and stressful ranges, however, the rate of heat failure more than doubles with each degree of warming.
To assess the potential impacts of future warming, the authors analysed temperature changes experienced by two species, Girella nigricans and Pheidole megacephala, using GBIF-mediated occurrences. These analyses showed that projected warming in the year 2100 will increase heat failure rate by up to 2,100% and 690% for the two species, respectively.
For context, an increase of 1,000% (tenfold) means that an ectotherm will experience 150 per cent of its lethal dose on a hot day, as opposed to 15 per cent in today's climate. An organism currently able to survive for 5 hours during a heatwave, would succumb to heat failure and death within 30 minutes.