Conservation physiology offers powerful approaches to develop mechanistic explanations of shifts in species’ biogeography putatively attributed to Global Warming. Nevertheless, a comparative framework that integrates the multiple physiological traits underlying species’ thermal biology is to date still lacking. Here I demonstrate the fundamental importance of integrating metabolic performance, thermal tolerance and plasticity to provide more accurate predictions on species’ relative vulnerability to Global Warming. Six Caridean species occurring in a common garden were selected as model and acclimated to four temperature treatments: 10, 15, 20 and 25 °C. The effect temperature on their metabolic rates and thermal tolerance limits was tested, and plasticity for these physiological abilities was calculated according to a Reaction Norm approach. Metabolic rate increased exponentially with increasing temperature in all the species examined (except in Pandalus montagui). Nevertheless, species living in thermally unstable environments (Palaemon elegans and Palaemonetes varians) showed higher temperature dependence of metabolism than their subtidal counterparts (Crangon crangon and Palaemon serratus), thereby appearing to be at greater risk from sub-lethal effects of Global Warming. By contrast, the hypothesis of an evolutionary/functional trade-off between thermal tolerance and its plasticity suggests that both the most heat-tolerant species (P. elegans, P. varians and C. crangon) and the most plastic species (P. serratus) are likely to be in danger from acute lethal effects of Global Warming. Both P. montagui and Palaemon macrodactylus are exceptions, appearing to be the most and the least vulnerable species to Global Warming respectively
