Data Sheet 1_Habitat type controls microarthropod community changes across a Magellanic sub-Antarctic elevation gradient.docx

IntroductionElevation gradients are often used as a proxy for climate change as they allow comparisons of ecological responses over much larger temporal and spatial scales than is possible through experimental manipulations.
MethodsHere, we tested how microarthropod communities (Collembola and Acari) are affected by climatic differences between sea level and 600 m a.s.l. on Navarino Island, in the Magellanic sub-Antarctic ecoregion of southern Chile (mean annual temperatures of 5.6 vs 3.1°C, respectively). We quantified microarthropod abundance, richness and community trait characteristics in dominant moss (Racomitrium lanuginosum and Polytrichum strictum) and lichen (Usnea trachycarpa, Pseudocyphellaria freycinetii and Stereocaulon alpinum) vegetation growing at both elevations. These moss and lichen genera are characterized by large morphological differences and allow testing of how habitat characteristics affect microarthropod community response across elevation gradients.
ResultsCollembola and Acari community composition differed between the low and high elevation sites. Total abundance levels of Acari were maintained in each habitat across elevation, whereas Collembola richness strongly declined (50%) at high elevation in the moss habitats. Acari community differences across elevation were driven by relative abundance changes whereas the Collembola community lost species at higher elevation. An anticipated decline of smaller eudaphic Collembola at high elevation was only observed in the moss Racomitrium, reflecting potentially lower temperature buffering capacity and shelter options compared to Polytrichum. Lichens mostly supported larger epigeic species irrespective of elevation. There were no consistent patterns linking microarthropod communities with habitat water holding capacity or water loss rates across the studied habitats and elevation.
DiscussionHabitat type and the genus of moss or lichen were associated with microarthropod community changes across elevation, including examples of declines, increases and no change. These findings highlight that community responses across gradients may not always relate to the generally hypothesized environmental variables (e.g. temperature variability) and that habitat characteristics should be taken into account when using elevation as a proxy for climate change.

引言
海拔梯度常被用作气候变化的替代指标（proxy），因其可实现比人工实验操控更大时空尺度下的生态响应对比。

方法
本研究以智利南部麦哲伦亚南极生态区的纳瓦里诺岛为研究区域，探究了海平面与海拔600米处的气候差异对微型节肢动物（microarthropod）群落的影响，该群落包含弹尾纲（Collembola）与蜱螨目（Acari）两类群，两地年平均气温分别为5.6℃与3.1℃。我们对两处海拔生境内的优势苔藓与地衣开展了微型节肢动物丰度、类群丰富度及群落功能性状特征的量化分析，所涉及的优势苔藓包括丛毛网藓（Racomitrium lanuginosum）与直叶金发藓（Polytrichum strictum），优势地衣包括长毛松萝（Usnea trachycarpa）、弗雷西内假杯点衣（Pseudocyphellaria freycinetii）与高山柱衣（Stereocaulon alpinum）。上述苔藓与地衣属类形态差异显著，可用于探究生境特征如何影响海拔梯度下的微型节肢动物群落响应。

结果
低海拔与高海拔样地的弹尾纲与蜱螨目群落组成存在显著差异。两处海拔生境内的蜱螨目总丰度均保持稳定，而苔藓生境中的弹尾纲类群丰富度在高海拔处大幅下降（降幅达50%）。海拔梯度对蜱螨目群落的影响源于其相对丰度的变化，而高海拔处弹尾纲群落则出现物种丢失现象。此前预期的高海拔处小型真土栖弹尾纲类群丰度下降现象，仅在丛毛网藓（Racomitrium lanuginosum）生境中被观测到，这反映出相较于直叶金发藓（Polytrichum strictum），丛毛网藓的温度缓冲能力与庇护场所供给可能更低。无论海拔高低，地衣生境主要支撑大型表栖类群。在本次研究涉及的生境与海拔梯度中，未发现微型节肢动物群落与生境持水能力或失水速率间存在一致关联模式。

讨论
海拔梯度下的微型节肢动物群落变化与生境类型以及苔藓/地衣属类密切相关，其变化模式包括丰度下降、上升以及无显著变化三类。本研究结果表明，梯度下的群落响应并非总能与普遍假设的环境变量（如温度波动）相契合，在利用海拔梯度作为气候变化替代指标时，应充分考虑生境特征的影响。