Thermal-safety margins and the necessity of thermoregulatory behavior across latitude and elevation

Abstract

Physiological thermal-tolerance limits of terrestrial ectotherms often exceed local air temperatures, implying a high degree of thermal safety (an excess of warm or cold thermal tolerance). However, air temperatures can be very different from the equilibrium body temperature of an individual ectotherm. Here, we compile thermal-tolerance limits of ectotherms across a wide range of latitudes and elevations and compare these thermal limits both to air and to operative body temperatures (theoretically equilibrated body temperatures) of small ectothermic animals during the warmest and coldest times of the year. We show that extreme operative body temperatures in exposed habitats match or exceed the physiological thermal limits of most ectotherms. Therefore, contrary to previous findings using air temperatures, most ectotherms do not have a physiological thermal-safety margin. They must therefore rely on behavior to avoid overheating during the warmest times, especially in the lowland tropics. Likewise, species living at temperate latitudes and in alpine habitats must retreat to avoid lethal cold exposure. Behavioral plasticity of habitat use and the energetic consequences of thermal retreats are therefore critical aspects of species' vulnerability to climate warming and extreme events. macrophysiology | operative temperature | climate sensitivity

Trading heat and hops for water: Dehydration effects on locomotor performance, thermal limits, and thermoregulatory behavior of a terrestrial toad

“…2011; Sherwood & Fu 2014; Sunday et al . 2014) may pose quite significant threats to the conservation of terrestrial amphibians (Todgham & Stillman 2013; Sunday et al . 2014; Nowakowski et al .…”

Plasticity in thermal tolerance has limited potential to buffer ectotherms from global warming

“…Thus, for lethal (this study) and sub-lethal [38] physiological traits, low-latitude taxa are not at a disadvantage with respect to plasticity. While there may be several reasons why tropical taxa are more susceptible to warming than high-latitude taxa [2,15,55,56], a lack of thermal plasticity is unlikely to be one of them. Similarly, it has been hypothesized that taxa adapted to the warmest habitats will be highly vulnerable to warming owing to small thermal safety margins and low plasticity in thermal tolerance caused by an expected trade-off between plasticity and inherent thermal tolerance [4,20,57].…”

“…Despite the potential importance of plasticity in dictating population vulnerability to climate change, calculations of overheating risk rarely take into account plasticity in thermal tolerance (e.g. [2,9]). Ignoring plasticity can affect estimations of absolute overheating risk, and lead to errors in assessing patterns of risk that may exist among taxa from different habitats or taxonomic groups [10].…”

Can acclimation of thermal tolerance, in adults and across generations, act as a buffer against climate change in tropical marine ectotherms?

“…These global patterns allow species vulnerability to climate warming to be assessed (e.g., Deutsch et al, 2008;Sunday et al, 2011;Sunday et al, 2014) and improve predictions of how species and populations will persist in the face of increasing global temperatures. These broad scale patterns can then be interpreted through organism-based studies that take species' ecological and evolutionary patterns into account (Polgar et al, 2015).…”