It is predicted that climate change will cause species extinctions and distributional shifts in coming decades, but data to validate these predictions are relatively scarce. Here, we compare recent and historical surveys for 48 Mexican lizard species at 200 sites. Since 1975, 12% of local populations have gone extinct. We verified physiological models of extinction risk with observed local extinctions and extended projections worldwide. Since 1975, we estimate that 4% of local populations have gone extinct worldwide, but by 2080 local extinctions are projected to reach 39% worldwide, and species extinctions may reach 20%. Global extinction projections were validated with local extinctions observed from 1975 to 2009 for regional biotas on four other continents, suggesting that lizards have already crossed a threshold for extinctions caused by climate change.

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During climate change, species are often assumed to shift their geographic distributions (geographic ranges) in order to track environmental conditions – niches – to which they are adapted. Recent work, however, suggests that the niches do not always remain conserved during climate change but shift instead, allowing populations to persist in place or expand into new areas. We assessed the extent of range and niche shifts in response to the warming climate after the Last Glacial Maximum (LGM) in the desert horned lizard (Phrynosoma platyrhinos), a species occupying the western deserts of North America. We used a phylogeographic approach with mitochondrial DNA sequences to approximate the species range during the LGM by identifying populations that exhibit a genetic signal of population stability versus those that exhibit a signal of a recent (likely post-LGM) geographic expansion. We then compared the climatic niche that the species occupies today with the niche it occupied during the LGM using two models of simulated LGM climate. The genetic analyses indicated that P. platyrhinos persisted within the southern Mojave and Sonoran deserts throughout the latest glacial period and expanded from these deserts northwards, into the western and eastern Great Basin, after the LGM. The climatic niche comparisons revealed that P. platyrhinos expanded its climatic niche after the LGM towards novel, warmer and drier climates that allowed it to persist within the southern deserts. Simultaneously, the species shifted its climatic niche towards greater temperature and precipitation fluctuations after the LGM. We concluded that climatic changes at the end of the LGM promoted both range and niche shifts in this lizard. The mechanism that allowed the species to shift its niche remains unknown, but phenotypic plasticity likely contributes to the species ability to adjust to climate change.

We derived physiological models that accurately predicted extinctions of Mexican and other lizards. Clusella-Trullas and Chown argue that global forecasts are unreliable without incorporating variance in microenvironmental temperatures, T e . Here, we show that T e variance is small relative to T e increases from climate warming. Thus, extinction forecasts are reliable ( R 2 ¼ 0:72) even without T e variance data. W e predicted extinctions of MexicanSceloporus lizards by deriving physiological models based on field (T b ) and preferred body temperatures (T p ), maximum daily air temperatures (T max ), and activity-time restrictions during reproduction, h r = cumulative hours/day when T e > T p (1). Clusella-Trullas and Chown (2) assert that our failure to include spatial heterogeneity in microenvironmental temperatures (T e )-and thus assess thermal opportunities at local population scales-overestimates h r , thereby inflating extinction forecasts. Contrary to their assertions, we did not simply apply h r , T max , and T b relations [equation S2 in (1)] to lizard families. We computed family-specific h r values using T b and T max -based distributional limits, adjusting h r [thereby scaling equation S2 in (1)] to each family. We also cross-validated h r estimates with available behavioral data [e.g., h r = 1.83, Liolaemus lutzae, table S7A in (1)]. Finally, we validated predicted extinctions derived from family-specific h r calibrations with observed extinctions across four other continents, including 192 species spanning seven families, not the single species implied by Clusella-Trullas and Chown (2).If local T e variation is biologically relevant, as Clusella-Trullas and Chown argue, then our model should poorly predict observed extinctions. In fact, the model derived for México accurately predicted other extinctions on four continents and across seven lizard families, explaining 72% of the variation (Table 1). Including additional moments of ectotherm temperature distributions (T e , T p , and T b ), as suggested by Clusella-Trullas and Chown (2), could refine predictions, but note that relatively little variation (28%) remains unexplained. More informative refinements would involve adding other climate data-such as duration, frequency, and intensity of warm spells, cloud cover (3, 4) ( Fig. 1), and precipitationand linking these to demography. To illustrate this point, we highlight data on S. mucronatus (5), which ceased reproduction at Zoquiapan in 1998, the year when four nearby weather stations recorded the highest T max during April through June [table S2 in (1)]. Based on historical reconstructions of T e and T max (Fig. 1), this 3-month warm spell greatly elevated T e at adjacent sites and caused reproductive arrest of S. mucronatus (5); S. mucronatus went extinct at two adjacent sites shortly thereafter [table S1 in (1)].To what extent does local T e variation affect extinction forecasts relative to historical T e excursions? Even when T e distributions exhibit skew or variance, the fraction of therma...