Abstract

B land and ocean temperatures are changing rapidly as a result of human activities that have substantially increased atmospheric concentrations of carbon dioxide and other greenhouse gases (Diffenbaugh and Field 2013; Laffoley and Baxter 2016). Predicting and managing the effects of global climate change require knowledge of population vulnerability (ie the propensity or predisposition to be adversely affected; IPCC 2014). While scientific literature lacks consensus regarding the definition of species vulnerability (Pacifici et al. 2015), researchers suggest that it is a function of both intrinsic and extrinsic factors and includes exposure, sensitivity, and adaptive capacity (Williams et al. 2008; Foden et al. 2013). Exposure is defined as the extent of climate change likely to be experienced by a species or place and depends on the rate and magnitude of climate change (temperature, precipitation, sealevel rise, etc) in habitats and regions occupied by the species (Williams et al. 2008). Sensitivity is the degree to which a system or species is affected by changes in climate (IPCC 2014) and can be determined by traits that are intrinsic to a species (Foden et al. 2013). Adaptive capacity is defined as the ability of systems, institutions, humans, and other organisms to adjust to potential damage, to take advantage of opportunities, or to respond to consequences (IPCC 2014). For species or populations, such capacity may be enhanced through natural selection and other evolutionary mechanisms, and it depends on both intrinsic factors (phenotypic plasticity, genetic diversity, evolutionary rates, dispersal and colonization ability) and extrinsic factors (rate, magnitude, and nature of climatic change) (Dawson et al. 2011). Changes in temperature can alter species distributions and phenology, species interactions, community diversity, and ecosystem function (Parmesan and Yohe 2003; Vasseur et al. 2014). Increases in temperature generally benefit population fitness until temperatures exceed a thermal optimum (Topt; Kingsolver and Huey 2008), after which population fitness often declines (Figure 1; Huey et al. 2012). Population thermal performance curves (TPCs) have facilitated climate adaptation planning and management by providing critical data for identifying species that are vulnerable to rising temperatures (Vasseur et al. 2014). Although experimental assessments of thermal sensitivity in survivorship, growth, and reproduction have a long history in both terrestrial (Huey and Kingsolver 1989) and marine (Kinne 1960) populations, these studies have only rarely included a sufficient range of temperature treatments to fully describe both the rise and fall of the fitness response. This has precluded their use in syntheses of species vulnerability requiring TPCs that capture species’ entire thermal response (eg Deutsch et al. 2008; Araújo et al. 2013). In order to evaluate the sensitivity of diverse and less studied taxa to warming, researchers need simple methods that would facilitate use of all existing information on population responses to temperature change (Williams et al. 2008; Huey et al. 2012; Nadeau et al. 2017). In the absence of full TPCs, potential proxies could include maximum critical temperature (the temperature above Topt at which mortality occurs), mean body temperature in the field, and preferred body temperature in the lab (Huey et al. 2012). However, these require meticulous experimental manipulations, and data therefore remain unavailable for most taxa and populations (but see Comte and Olden [2017] for an analysis of freshwater and marine rayfinned fishes). In this study, we examined the ability of mean annual temperature (MAT) to predict the sensitivity of taxonomically Predicting the sensitivity of marine populations to rising temperatures