Boundaries between vegetation types, known as ecotones, can be dynamic in response to climatic changes. The North American Great Plains includes a forest-grassland ecotone in the southcentral United States that has expanded and contracted in recent decades in response to historical periods of drought and pluvial conditions. This dynamic region also marks a western distributional limit for many passerine birds that typically breed in forests of the eastern United States. To better understand the influence that variability can exert on broad-scale biodiversity, we explored historical longitudinal shifts in the western extent of breeding ranges of eastern forest songbirds in response to the variable climate of the southern Great Plains. We used climatic niche modeling to estimate current distributional limits of nine species of forest-breeding passerines from 30-year average climate conditions from 1980 to 2010. During this time, the southern Great Plains experienced an unprecedented wet period without periodic multi-year droughts that characterized the region's long-term climate from the early 1900s. Species’ climatic niche models were then projected onto two historical drought periods: 1952–1958 and 1966–1972. Threshold models for each of the three time periods revealed dramatic breeding range contraction and expansion along the forest-grassland ecotone. Precipitation was the most important climate variable defining breeding ranges of these nine eastern forest songbirds. Range limits extended farther west into southern Great Plains during the more recent pluvial conditions of 1980–2010 and contracted during historical drought periods. An independent dataset from BBS was used to validate 1966–1972 range limit projections. Periods of lower precipitation in the forest-grassland ecotone are likely responsible for limiting the western extent of eastern forest songbird breeding distributions. Projected increases in temperature and drought conditions in the southern Great Plains associated with climate change may reverse range expansions observed in the past 30 years.

中文翻译：

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变降水导致林草交错带森林鸣禽的动态范围限制

植被类型之间的边界，称为生态带，可以随着气候变化而动态变化。北美大平原包括美国中南部的森林-草原交错带，近几十年来，该交错带因历史时期的干旱和多雨条件而扩大和收缩。这个充满活力的地区也标志着许多通常在美国东部森林中繁殖的雀类鸟类的西部分布限制。为了更好地了解变异对大范围生物多样性的影响，我们探索了东部森林鸣禽繁殖范围西部范围的历史纵向变化，以响应大平原南部的多变气候。我们使用气候生态位模型估计了 1980 年至 2010 年 30 年平均气候条件下 9 种森林繁殖雀科动物的当前分布范围。在此期间，大平原南部经历了前所未有的湿润期，没有出现周期性的多年干旱描述了该地区自 1900 年代初以来的长期气候。然后将物种的气候生态位模型预测到两个历史干旱时期：1952-1958 和 1966-1972。三个时间段中的每一个的阈值模型都揭示了沿着森林-草地交错带的急剧繁殖范围收缩和扩张。降水是决定这九种东部森林鸣禽繁殖范围的最重要的气候变量。在 1980 年至 2010 年的较新的雨洪条件下，范围限制向西延伸到大平原南部，并在历史干旱时期缩小。来自 BBS 的独立数据集用于验证 1966-1972 范围限制预测。森林-草地交错带中降水量较低的时期可能是限制东部森林鸣禽繁殖分布的西部范围的原因。与气候变化相关的南部大平原地区温度和干旱条件的预计增加可能会逆转过去 30 年观察到的范围扩大。森林-草地交错带中降水量较低的时期可能是限制东部森林鸣禽繁殖分布的西部范围的原因。与气候变化相关的南部大平原地区温度和干旱条件的预计增加可能会逆转过去 30 年观察到的范围扩大。森林-草地交错带中降水量较低的时期可能是限制东部森林鸣禽繁殖分布的西部范围的原因。与气候变化相关的南部大平原的温度和干旱条件的预计增加可能会逆转过去 30 年观察到的范围扩大。