Abstract North American deserts are warming and becoming more arid at rates that exceed global averages. Desert lizard populations are typically dependent on plant and arthropod food resources catalyzed by variations in aridity. Shifts in those lizard distributions coincident with increasing aridity therefore present an opportunity to document responses to modern climate change as it is happening. Here, we analyzed observation frequencies across an elevation gradient for seven lizard species, comparing a historical dataset (1958–1972) to recent observations (2014–2018) within Joshua Tree National Park, a landscape straddling the Mojave and Colorado Deserts in southern California. Phrynosoma platyrhinos, Aspidoscelis tigris, and Callisaurus draconoides, now appear to occupy new, higher elevation habitats compared to the historical baseline. Except for Sceloporus occidentalis, observation records for each species indicated shifts toward the upper elevations of their ranges. Observations for Uta stansburiana, C. draconoides and A. tigris each shifted their mean elevation upslope ≥10%. Phrynosoma platyrhinos and A. tigris shifted their maximum elevations by ≥15%. To assess whether those elevation shifts could then be corroborated with independent data, we compared the historic-recent observation data with plot-based surveys where we measured lizard densities varying with elevation and rainfall levels from 2014 to 2019. Those historical-recent shifts paralleled changes in lizard densities over the same elevation gradient, with statistical support for the upslope shifts identified for U. stansburiana, A. tigris and, S. magister. Additionally, despite increases in warming and aridity, we found species-specific elevations where local conditions are supporting higher population densities and that may represent climate refugia.

中文翻译：

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应对干旱加剧：约书亚树国家公园 50 年间蜥蜴范围变化的证据

摘要 北美沙漠正在以超过全球平均水平的速度变暖并变得更加干旱。沙漠蜥蜴种群通常依赖于干旱变化催化的植物和节肢动物食物资源。这些蜥蜴分布的变化与干旱的增加同时发生，因此提供了记录对正在发生的现代气候变化的反应的机会。在这里，我们分析了七种蜥蜴物种在海拔梯度上的观测频率，将历史数据集（1958-1972）与最近在约书亚树国家公园内的观测（2014-2018）进行了比较，这是一个横跨加利福尼亚南部莫哈韦沙漠和科罗拉多沙漠的景观。与历史基线相比，Phrynosoma platyrhinos、Aspidoscelis tigris 和 Callisaurus draconoides 现在似乎占据了新的、海拔更高的栖息地。除 Sceloporus occidentalis 外，每个物种的观察记录都表明向其分布范围的较高海拔移动。对 Uta stansburiana、C. draconoides 和 A. tigris 的观察均将其平均海拔上升了 10% 以上。Phrynosoma platyrhinos 和 A. tigris 将它们的最大海拔移动了≥15%。为了评估这些海拔变化是否可以用独立数据证实，我们将历史最近的观察数据与基于地块的调查进行了比较，在这些调查中，我们测量了 2014 年至 2019 年随海拔和降雨量水平变化的蜥蜴密度。这些历史最近的变化与变化平行在同一海拔梯度上的蜥蜴密度中，统计支持为 U. stansburiana、A. tigris 和 S. magister 确定的上坡位移。此外，尽管气候变暖和干旱加剧，