Tomecek John M, Pierce Brian L, Reyna Kelly S, Peterson Markus J
Department of Wildlife and Fisheries Sciences, Texas A&M University, College Station, TX, USA.
Texas A&M Natural Resources Institute, Texas A&M University, College Station, TX, USA.
PeerJ. 2017 Aug 18;5:e3709. doi: 10.7717/peerj.3709. eCollection 2017.
Ecologists have long recognized the influence that environmental conditions have on abundance and range extent of animal species. We used the northern bobwhite (; hereafter bobwhite) as a model species for studying how microclimates serve as refuge against severe weather conditions. This species serves as an indicator or umbrella species for other sensitive ground-nesting, grassland obligate species. We conducted a mensurative field experiment in the rolling plains of Texas, USA, a semi-arid ecosystem on the southwestern periphery of bobwhite range, to determine whether native bunch grasses, apparently suitable for bobwhite nesting, could reduce ambient temperature below levels harmful for eggs. During the nesting season, we compared temperature and relative humidity readings at daily heat maxima (i.e., the 3 h during each day with highest temperatures) during the nesting season over the course of two years at 63 suitable nest sites paired with 63 random locations ( = 126) using two sensors at ∼10 and ∼60 cm above ground level. Mean temperature at nest height was 2.3% cooler at nest sites (35.99 °C ± 0.07 SE) compared to random locations (36.81 °C ± 0.07 SE); at ambient height, nest sites were slightly cooler (32.78 °C ± 0.06 SE) than random location (32.99 °C ± 0.06 SE). Mean relative humidity at nest sites was greater at nest height (34.53% ± 0.112 SE) and ambient height (36.22% ± 0.10 SE) compared to random locations at nest (33.35% ± 0.12 SE) and ambient height (35.75% ± 0.10 SE). Based on these results, cover at sites that appear visually suitable for nesting by bobwhites and other ground nesting birds provided adequate thermal refuge in the rolling plains by maintaining cooler, moister microclimates than surrounding non-nesting locations. Post-hoc analyses of data revealed that habitat conditions surrounding suitable nest sites strongly influenced thermal suitability of the substrate. Given that eggs of bobwhites and probably other species would experience lethal temperatures without these thermal refuges in the context of proper habitat condition, nesting vegetation is a critical component of niche space for bobwhites and other ground nesting birds in semi-arid regions. Many contemporary land uses, however, degrade or destroy bunch grasses and grassland systems, and thus decrease landscape inhabitability. Conservationists working with obligate grassland species that require bunch grasses in semi-arid regions should develop land management strategies that maximize the availability of these thermal refuges across space and time.
长期以来，生态学家们一直认识到环境条件对动物物种数量和分布范围的影响。我们以北部白喉鹑（以下简称白喉鹑）作为模式物种，来研究小气候如何为抵御恶劣天气提供庇护。该物种是其他敏感的地面筑巢、专性草地物种的指示物种或伞护物种。我们在美国得克萨斯州的起伏平原（白喉鹑分布范围西南边缘的一个半干旱生态系统）进行了一项测量性野外实验，以确定看似适合白喉鹑筑巢的原生丛生禾本科植物是否能将环境温度降低到对卵无害的水平以下。在筑巢季节，我们在两年时间里，于63个合适的筑巢地点及与之配对的63个随机地点（共126个），使用两个分别位于离地面约10厘米和60厘米高度的传感器，比较了筑巢季节每日高温时段（即每天温度最高的3小时）的温度和相对湿度读数。筑巢地点巢高的平均温度（35.99℃±0.07标准误）比随机地点（36.81℃±0.07标准误）低2.3%；在环境高度，筑巢地点（32.78℃±0.06标准误）比随机地点（32.99℃±0.06标准误）略低。与巢和环境高度的随机地点相比，筑巢地点巢高（34.53%±0.112标准误）和环境高度（36.22%±0.10标准误）的平均相对湿度更高，巢处随机地点为（33.35%±0.12标准误），环境高度为（35.75%±0.10标准误）。基于这些结果，在视觉上看似适合白喉鹑和其他地面筑巢鸟类筑巢的地点所提供的植被覆盖，通过维持比周围非筑巢地点更凉爽、更湿润的小气候，在起伏平原上提供了充足的热庇护。对数据的事后分析表明，合适筑巢地点周围的栖息地条件强烈影响了基质的热适宜性。鉴于在适当的栖息地条件下，如果没有这些热庇护，白喉鹑以及可能其他物种的卵会经历致死温度，筑巢植被是半干旱地区白喉鹑和其他地面筑巢鸟类生态位空间的关键组成部分。然而，许多当代土地利用方式会使丛生禾本科植物和草地系统退化或遭到破坏，从而降低景观的宜居性。与半干旱地区需要丛生禾本科植物的专性草地物种打交道的保护主义者，应制定土地管理策略，以在空间和时间上最大限度地提供这些热庇护。
