Journal of Ecology ( IF 5.3 ) Pub Date : 2024-08-22 , DOI: 10.1111/1365-2745.14401 Norbert Helm 1, 2 , Kryštof Chytrý 1, 2 , Karl Hülber 1 , Dietmar Moser 1 , Johannes Wessely 1 , Andreas Gattringer 1 , Johannes Hausharter 1, 2 , Harald Pauli 2 , Manuela Winkler 3 , Patrick Saccone 3 , Andrea Lamprecht 3 , Martin Rutzinger 4 , Andreas Mayr 4 , Andreas Kollert 4 , Stefan Dullinger 1
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1 INTRODUCTION
The world is warming rapidly and high mountains experience even above-average rates of temperature increase (Pepin et al., 2015). As a consequence, species of the alpine flora must either adapt to the new climatic conditions, follow their suitable climatic niche or face extinction (Dullinger et al., 2012; Engler et al., 2011; Graae et al., 2018). Indeed, resurvey studies have noted increased colonization and extinction rates at upper and lower limits of species' local distribution ranges indicating an already ongoing redistribution of alpine species (Pauli et al., 2012; Rumpf et al., 2018; Steinbauer et al., 2020; Wiens, 2016). However, several studies demonstrated that this redistribution is lagging behind the pace of climate change, likely due to other assembly factors besides environmental filtering (Rumpf et al., 2019; Vittoz et al., 2009). In fact, climate-driven redistribution requires that species reach and establish in sites that become suitable and go extinct at sites which no longer match their requirements. The consequent delays in redistribution suggest that the distribution of alpine species is co-determined by limitations in dispersal, resistance against establishment by resident communities, as well as strategies that allow persistence under unsuitable conditions (Alexander et al., 2018; Dullinger et al., 2012; Von Holle et al., 2003). More generally, the lagged response to climate change highlights that the assembly of alpine plant communities is co-determined by environmental sorting, biotic interactions and dispersal limitation. Although the joint impact of these three factors on community assembly is generally acknowledged (Vellend, 2010), they do not have received comparable attention in alpine plant ecology yet.
The long history of alpine plant ecology has put a strong focus on environmental sorting, emphasizing the role of meso- and microscale variation in snow cover, ambient temperature, nutrient and water supply (Billings & Mooney, 1968; Blonder et al., 2018; Körner, 2021; Leuschner & Ellenberg, 2017). More recently, the impact of biotic interactions on alpine plant communities was highlighted, especially the role of facilitation among neighbour plants (Anthelme et al., 2014; Cavieres et al., 2008, 2014; Choler et al., 2001), respectively the interplay between environmental sorting and plant–plant interactions (Bektaş et al., 2023; Callaway et al., 2002). By contrast, the role of neutral processes has received less attention, although seed sowing and transplantation experiments suggested that dispersal limitation might be an important determinant of species distribution at the landscape-scale (Dullinger & Hülber, 2011), and modelling studies indicated that, despite occasional long-distance dispersal events, the vast majority of plant propagules only move over very short distances (Tackenberg & Stöcklin, 2008). Vice versa, alpine plant populations far below the tree line, e.g. in avalanche paths or along riverbeds (Malanson & Butler, 1984) suggest that populations may persist under warmer conditions if either competition pressure is reduced and/or propagules are supplied at a sufficient rate, i.e. via source-sink dynamics. Taken together, evidence suggest that biotic interactions and dispersal limitation are vital for the assembly of alpine plant communities, or their re-assembly in a changing climate. Nevertheless, studies that explicitly compare the relative roles of dispersal and biotic interactions versus environmental sorting for alpine plant community assembly are largely lacking so far.
The interest in climate change effects on mountain plant communities has motivated the establishment of the Global Observation Research Initiative in Alpine Environments (Pauli et al., 2005) which aims to monitor long-term changes in alpine plant communities. The oldest monitoring site of GLORIA was established in 1994 at the alpine-nival ecotone of Mt. Schrankogel in the Austrian Alps and has been resurveyed every 10 years since. The resurvey in 2014 revealed a slow transformation of communities towards a more warmth-demanding and drought-tolerant species composition (Lamprecht et al., 2018). However, while the imprint of climate warming on species turn-over across monitored plots is clearly detectable, the relative contributions of environmental conditions, propagule supply and biotic interactions to the re-assembly of the individual communities have not yet been analysed. Here, we used this dataset to examine the impact of these three factors on colonization and extirpation events of 31 vascular plant species in 492 permanent plots in the alpine-nival ecotone over 20 years of monitoring. We therefore coupled the data from these permanent plots with those of 899 additional 1 m2 plots sampled across the entire above-tree line vegetation of Mt. Schrankogel in 2021/2022, which we used for fine-scale habitat suitability modelling. We then applied the fitted models to the 492 permanent plots and used the projected probability of occurrence as a metric for environmental suitability. We combined this suitability metric with a spatial kernel of source plant density, as an indicator of propagule pressure, and an estimate of the resident community's biomass as a proxy of plant–plant interaction intensity and used R2 statistic to compare their relative effects on changes in plant occurrences. We hypothesized that (1) the likelihood of colonizations will increase, and the likelihood of extirpations decrease with increasing habitat suitability; (2) colonizations will positively, and extirpations negatively correlate with propagule pressure; and (3) higher plant biomass values will have a positive effect on both colonization and persistence due to facilitative effects of neighbours under the harsh conditions of the alpine–nival ecotone. With respect to the relative strength of these effects we had no clear a-priori expectation. Nevertheless, we generally hypothesized that both dispersal limitation and species interactions would significantly improve the predictability of both colonizations and extirpations as compared to considering environmental sorting, i.e. habitat suitability, alone.
中文翻译：
精细高山植物群落组装：环境排序、扩散过程和物种相互作用的相对作用
1 引言
世界正在迅速变暖，高山地区的温度上升速度甚至高于平均水平（Pepin et al.， 2015）。因此，高山植物群的物种必须适应新的气候条件，遵循合适的气候生态位，否则将面临灭绝（Dullinger 等人，2012 年;Engler 等人，2011 年;Graae et al.， 2018）。事实上，重新调查研究指出，物种局部分布范围上限和下限的定殖和灭绝率增加，这表明高山物种的重新分布已经在进行中（Pauli 等人，2012 年;Rumpf et al.， 2018;Steinbauer等人，2020 年;Wiens，2016 年）。然而，几项研究表明，这种再分配落后于气候变化的步伐，这可能是由于环境过滤以外的其他组装因素（Rumpf et al.， 2019;Vittoz et al.， 2009）。事实上，气候驱动的再分配要求物种到达并定居在变得合适的地点，并在不再符合其要求的地点灭绝。随之而来的再分布延迟表明，高山物种的分布是由传播的限制、对常驻群落建立的抵抗以及允许在不合适的条件下持续存在的策略共同决定的（Alexander et al.， 2018;Dullinger 等人，2012 年;Von Holle et al.， 2003）。更一般地说，对气候变化的滞后响应突出表明，高山植物群落的组装是由环境分类、生物相互作用和扩散限制共同决定的。尽管这三个因素对群落组装的共同影响被普遍承认（Vellend，2010），但它们在高山植物生态学中尚未得到同等的关注。
高山植物生态学的悠久历史使得环境分类受到强烈关注，强调中尺度和微观尺度变化在积雪覆盖、环境温度、营养和水供应中的作用（Billings & Mooney， 1968;Blonder et al.， 2018;Körner，2021 年;Leuschner & Ellenberg，2017 年）。最近，强调了生物相互作用对高山植物群落的影响，特别是邻近植物之间的促进作用（Anthelme et al.， 2014;Cavieres 等人，2008 年、2014 年;Choler等人，2001 年），分别研究了环境分类和植物-植物相互作用之间的相互作用（Bektaş 等人，2023 年;Callaway et al.， 2002）。相比之下，中性过程的作用受到的关注较少，尽管种子播种和移植实验表明，在景观尺度上，传播限制可能是物种分布的重要决定因素（Dullinger & Hülber， 2011），并且建模研究表明，尽管偶尔会发生长距离传播事件，但绝大多数植物繁殖体只能在非常短的距离内移动（Tackenberg & Stöcklin， 反之亦然，高山植物种群远低于树线，例如在雪崩路径或河床沿线（Malanson & Butler， 1984）表明，如果竞争压力降低和/或繁殖体以足够的速率供应，即通过源-汇动力学，种群可能会在温暖的条件下持续存在。综上所述，证据表明，生物相互作用和扩散限制对于高山植物群落的组装或它们在不断变化的气候中的重新组装至关重要。 然而，到目前为止，在很大程度上缺乏明确比较扩散和生物相互作用与环境分类对高山植物群落组装的相对作用的研究。
对气候变化对山地植物群落影响的兴趣促使建立了高山环境全球观测研究计划（Pauli et al.， 2005），旨在监测高山植物群落的长期变化。GLORIA 最古老的监测站点于 1994 年在奥地利阿尔卑斯山的 Schrankogel 山的阿尔卑斯-新世纪交错带建立，此后每 10 年重新调查一次。2014 年的重新调查显示，群落向更需要温暖和更耐旱的物种组成缓慢转变（Lamprecht 等，2018）。然而，虽然气候变暖对监测地块物种更替的影响是可以清楚地检测到的，但环境条件、繁殖体供应和生物相互作用对单个群落重新组装的相对贡献尚未得到分析。在这里，我们使用这个数据集来研究这三个因素对 20 年监测中 31 种维管束植物物种在高山-尼瓦尔交错带 492 个永久样地的定植和灭绝事件的影响。因此，我们将这些永久地块的数据与 2021/2022 年在施兰科格尔山整个树线上植被中采样的 899 个额外的 1 m 2 地块的数据相结合，我们将其用于精细的栖息地适宜性建模。然后，我们将拟合模型应用于 492 个永久地块，并使用预计的发生概率作为环境适宜性的指标。 我们将该适宜性指标与源植物密度的空间内核相结合，作为繁殖体压力的指标，并将常驻群落生物量的估计值作为植物-植物相互作用强度的代表，并使用 R 2 统计量来比较它们对植物发生变化的相对影响。我们假设 （1） 定植的可能性会增加，灭绝的可能性会随着栖息地适宜性的提高而降低;（2） 定殖与繁殖压力呈正相关，灭绝呈负相关;（3） 较高的植物生物量值将对定殖和持久性产生积极影响，因为在阿尔卑斯-尼瓦尔交错带的恶劣条件下，邻居的促进作用。关于这些影响的相对强度，我们没有明确的先验期望。尽管如此，我们通常假设，与单独考虑环境排序（即栖息地适宜性）相比，扩散限制和物种相互作用都会显着提高定植和灭绝的可预测性。
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