Quantifying thermal extremes and biological variation to predict evolutionary responses to changing climate

Abstract

Central ideas from thermal biology, including thermal performance curves and tolerances, have been widely used to evaluate how changes in environmental means and variances generate changes in fitness, selection and microevolution in response to climate change. We summarize the opportunities and challenges for extending this approach to understanding the consequences of extreme climatic events. Using statistical tools from extreme value theory, we show how distributions of thermal extremes vary with latitude, time scale and climate change. Second, we review how performance curves and tolerances have been used to predict the fitness and evolutionary responses to climate change and climate gradients. Performance curves and tolerances change with prior thermal history and with time scale, complicating their use for predicting responses to thermal extremes. Third, we describe several recent case studies showing how infrequent extreme events can have outsized effects on the evolution of performance curves and heat tolerance. A key issue is whether thermal extremes affect reproduction or survival, and how these combine to determine overall fitness. We argue that a greater focus on tails-in the distribution of environmental extremes, and in the upper ends of performance curves-is needed to understand the consequences of extreme events.This article is part of the themed issue 'Behavioural, ecological and evolutionary responses to extreme climatic events'.

Evolution caused by extreme events

“…How organisms respond to extreme environmental conditions depends in part on their behaviour, prior exposure to extremes, how phenotypically plastic they are, the degree to which they are genetically variable in fitness-related traits, and demographic factors such as lifespan and dispersal (gene flow) [25], as well as the magnitude of deviations from average environmental conditions and on how long these conditions persist relative to the lifespan of organisms. The rate and duration of environmental change in extreme conditions may be more important than the magnitude of change in determining whether the outcome is extinction, a shift in geographical distribution or local evolution and persistence [20,[26][27][28].…”

Behavioural, ecological and evolutionary responses to extreme climatic events: challenges and directions

“…For example, climate extremes may cause adaptations in thermal tolerance to evolve (e.g. [35]), while climate variability may lead to the evolution of bet-hedging strategies. As another example, population biologists have long known that key metrics like the long-term population growth rate, extinction risk and fitness are affected by both the mean and variability in the annual performance [36,37].…”

“…Another goal was to invite contributions from different fields that synthesize the ecological [2,18] and evolutionary literature on ECEs [7,35] and combine this with research papers that illustrate ways to make progress in answering important and interesting conceptual questions. The inclusion of contributions from such disparate fields as behavioural plasticity [23], community ecology [18] and evolution of thermal tolerance [35] was specifically chosen to highlight that these fields deal with similar challenges (e.g. they study events that are rare with respect to the duration of most studies in the wild), but also to illustrate that they can provide parallel insights (see later this section).…”

“…A literature review shows that single event studies using experimental or opportunistic studies tend to be short-term, while only long-term observational studies that accidentally experienced an ECE investigated delayed responses. Moreover, besides the obvious difficulty of estimating the biological response from a single event, another limitation is that it prevents assessment on how any response depends on the state of the study system (see §3 this study, [35]). They propose a data-and theory-driven pathway for how single event studies may improve our understanding of ECEs, but for the former pathway the required information for meta-analysis is typically not reported, while for the latter rstb.royalsocietypublishing.org Phil.…”

“…Another major parallel among studies in this theme issue appears to be that responses are highly idiosyncratic, indicating that generalization of ECE impacts is difficult and predictability low. For example, evolutionary responses in thermal tolerance in response to extremes can depend on the climatic history and amount of variability organisms previously experienced [35], and evolutionary change is often strongly mediated by changes in species interactions, which vary widely among ecosystems [7]. Behaviourally plastic responses may depend on the habitat type individuals live in [23] or on their energy reserves [20], while demographic responses can be highly age-dependent [34].…”