DISSERTATION RESEARCH: Making the transition: Comparing avian biogeographic responses to climate change across biomes

该项目将研究气候变暖对莫哈韦沙漠、索诺兰沙漠和大盆地沙漠鸟类群落的影响。这些沙漠有着不同的气候、植被和动物群落，在过去的50年里，它们都经历了逐渐变暖的过程。这项研究将利用一种独特的资源：在当前变暖开始之前，对1904年至1945年发生的沙漠动物进行系统计数。这些调查提供了人类引起的生态变化之前的沙漠生态系统健康的早期视图。在大盆地的30个地点和莫哈韦的69个地点进行的重新调查将提供100多种鸟类当前丰度的数据。这项研究将评估持续变暖的索诺兰沙漠和莫哈韦沙漠的物种是否正在向变暖较少的大盆地沙漠扩张，或者两种类型的沙漠之间的区域是否成为物种从一种扩展到另一种的障碍。这项研究还将增加对单个物种的地理范围如何应对气候变化的认识，通过确定物种是否独立地改变它们的范围，从而导致鸟类群落的重组，或者如果物种做出类似的反应，导致整个物种共同移动它们的范围。在气候变化热点（西南沙漠），利用独特的历史资源（格林内尔时代的调查），允许在大空间尺度上检查殖民化和灭绝过程，本研究将量化20世纪的变暖和干燥对鸟类生物地理分布的影响。在气候显著变暖之前对大盆地沙漠30个地点进行的鸟类重新调查，将补充对莫哈韦沙漠69个沙漠地点的重新调查，莫哈韦沙漠南部与索诺兰沙漠过渡，北部与大盆地沙漠过渡。本研究考察了温暖沙漠（索诺兰沙漠和莫哈韦沙漠）和寒冷沙漠（大盆地）鸟类群落结构随时间和空间的变化，以及沙漠之间的过渡带如何影响对气候变化的生物地理响应。了解莫哈韦-大盆地过渡带的分布变化将有助于评估温暖沙漠的物种是否正在向寒冷沙漠扩张，或者过渡带是否是向北扩张的障碍。如果温暖沙漠物种的南部边界也在缩小，鸟类向北扩张的障碍可能会导致范围的缩小。

This project will examine the impact of warming climate on bird communities in the Mojave, Sonoran, and Great Basin Deserts. These deserts have different climates, vegetation, and animal communities, and all have experienced gradually warmer temperatures over the last fifty years. This study will make use of a unique resource: systematic counts of desert animals that occurred from 1904 to 1945, before the onset of current warming. These surveys provide an early view of desert ecosystem health prior to human-caused ecological changes. Re-surveys at 30 sites across the Great Basin and 69 sites across the Mojave will provide data on the current abundance of over 100 bird species. This study will evaluate whether species of the Sonoran and Mojave deserts, which continue to warm, are expanding into the Great Basin desert, which as warmed less, or whether the area between the two types of deserts acts as a barrier to expansion of species from one to the other. This study will also increase knowledge of how the geographic ranges of individual species respond to climate change by determining if species shift their ranges independently, resulting in a reshuffling of bird communities, or if species respond similarly, resulting in entire sets of species moving their ranges together.In a climate change hotspot (the desert southwest), using a unique historical resource (Grinnell-era surveys) that allows examination of colonization and extinction processes at a large spatial scale, this study will quantify how rapid 20th century warming and drying influence avian biogeographic distributions. Avian re-surveys at 30 sites in the Great Basin deserts originally visited prior to significant climate warming will complement re-surveys at 69 desert sites in the Mojave Desert, its southern transition with the Sonoran, and its northern transition with the Great Basin desert. This study examines how avian community structure varies over time and space across warm (Sonoran and Mojave) and cold (Great Basin) deserts, and how the transition zone between the deserts impacts the biogeographic response to climate change. Understanding distributional change at the Mojave-Great Basin transition zone will enable the evaluation of whether species of the warm deserts are expanding into the cold desert, or whether the transition zone is a barrier to northward expansion. Barriers to northward expansion for birds could result in range collapse if the southern limits of warm desert species are also contracting.