![]() ![]() Whilst recent theory underscores the importance of environmental predictability in determining the slope of the evolved reaction norm for a given trait (i.e., how much plasticity can occur), a hitherto neglected possibility is that the rate of plasticity might be a more dynamic component of this relationship than previously assumed. Although recent advances in the field provide indication of the aspects of environmental change where RPP rates may be of particular ecological relevance, we observe that current theoretical models do not consider the evolutionary potential of the rate of RPP. Here, we examine the potential for better understanding how organisms overcome environmental challenges within their own lifetimes by scrutinizing a somewhat overlooked aspect of RPP, namely the rate at which it can occur. With rapid and less predictable environmental change emerging as the 'new norm', understanding how individuals tolerate environmental stress via plastic, often reversible changes to the phenotype (i.e., reversible phenotypic plasticity, RPP), remains a key issue in ecology. The persistence of each population depends not just on the range of tolerance phenotypes in the species as a whole, but on the distribution of those phenotypes among and within populations (Redrawn from ). (b) With a narrower range of phenotypes within populations and local adaptation, neither population persists, although population II could persist with gene flow from population I. ![]() (a) With a broad range of phenotypes within populations and no local adaptation, both populations persist. Populations can persist if they have some tolerance values lying above the new threshold. Solid line shows current gradient dashed line shows the future gradient. In this simplified scenario, box plots show the hypothetical distribution of temperature-tolerance phenotypes in two populations lying along a latitudinal temperature gradient. Our results suggest that models assuming a uniform climatic envelope may greatly underestimate extinction risk in species with strong local adaptation.Ĭorrelative models of species' distributions may underestimate extinction risk if individual populations contain a narrower range of tolerance phenotypes than the species as a whole. Thus, plasticity and adaptation appear to have limited capacity to buffer these isolated populations against further increases in temperature. ![]() Finally, in four populations there was no increase in thermal tolerance between generations 5 and 10 of selection, suggesting that standing variation had already been depleted. Moreover, heat-tolerant phenotypes observed in low-latitude populations cannot be achieved in high-latitude populations, either through acclimation or 10 generations of strong selection. Tigriopus californicus exhibit striking local adaptation to temperature, with less than 1 per cent of the total quantitative variance for thermal tolerance partitioned within populations. We test the extent of such variation in the broadly distributed tidepool copepod Tigriopus californicus using laboratory rearing and selection experiments to quantify thermal tolerance and scope for adaptation in eight populations spanning more than 17° of latitude. Although recent discussions have questioned this assumption, few empirical studies have characterized intraspecific patterns of genetic variation in traits directly related to environmental tolerance limits. Most models predicting biological responses to environmental change assume that species' climatic envelopes are homogeneous both in space and time. The extent to which acclimation and genetic adaptation might buffer natural populations against climate change is largely unknown.
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