Department of Animal Ecology and Tropical Biology, Biocenter, University of Würzburg, Würzburg, Germany.
Université Paris-Saclay, CNRS, IRD, UMR Évolution, Génomes, Comportement et Écologie, Gif-sur-Yvette, France.
Ecology. 2022 Jul;103(7):e3712. doi: 10.1002/ecy.3712. Epub 2022 Apr 27.
Environmental gradients generate and maintain biodiversity on Earth. Mountain slopes are among the most pronounced terrestrial environmental gradients, and the elevational structure of species and their interactions can provide unique insight into the processes that govern community assembly and function in mountain ecosystems. We recorded bumble bee-flower interactions over 3 years along a 1400-m elevational gradient in the German Alps. Using nonlinear modeling techniques, we analyzed elevational patterns at the levels of abundance, species richness, species β-diversity, and interaction β-diversity. Though floral richness exhibited a midelevation peak, bumble bee richness increased with elevation before leveling off at the highest sites, demonstrating the exceptional adaptation of these bees to cold temperatures and short growing seasons. In terms of abundance, though, bumble bees exhibited divergent species-level responses to elevation, with a clear separation between species preferring low versus high elevations. Overall interaction β-diversity was mainly caused by strong turnover in the floral community, which exhibited a well-defined threshold of β-diversity rate at the tree line ecotone. Interaction β-diversity increased sharply at the upper extreme of the elevation gradient (1800-2000 m), an interval over which we also saw steep decline in floral richness and abundance. Turnover of bumble bees along the elevation gradient was modest, with the highest rate of β-diversity occurring over the interval from low- to mid-elevation sites. The contrast between the relative robustness bumble bee communities and sensitivity of plant communities to the elevational gradient in our study suggests that the strongest effects of climate change on mountain bumble bees may be indirect effects mediated by the responses of their floral hosts, though bumble bee species that specialize in high-elevation habitats may also experience significant direct effects of warming.
环境梯度在地球上产生并维持生物多样性。山坡是最明显的陆地环境梯度之一，物种的海拔结构及其相互作用可以为理解控制山地生态系统群落组装和功能的过程提供独特的视角。我们在德国阿尔卑斯山的 1400 米海拔梯度上，连续 3 年记录了熊蜂-花的相互作用。我们使用非线性建模技术，分析了丰度、物种丰富度、物种β多样性和相互作用β多样性的海拔模式。虽然花卉丰富度表现出中海拔峰值，但熊蜂丰富度随海拔升高而增加，在最高处达到稳定，这表明这些蜜蜂对低温和短生长季节具有特殊的适应能力。然而，就丰度而言，熊蜂对海拔的物种水平响应表现出不同的趋势，低海拔和高海拔的物种之间存在明显的分离。总的来说，相互作用β多样性主要是由花卉群落的强烈更替引起的，在森林线生态交错带表现出β多样性率的明确阈值。在海拔梯度的上极端（1800-2000 米），相互作用β多样性急剧增加，在这个区间，我们还看到花卉丰富度和丰度的急剧下降。熊蜂沿着海拔梯度的更替幅度适中，β多样性的最高速率发生在低海拔到中海拔之间的区间。本研究中，熊蜂群落相对稳健而植物群落对海拔梯度敏感的对比表明，气候变化对山地熊蜂的影响可能主要是间接的，通过其花卉宿主的反应来介导，尽管专门适应高海拔生境的熊蜂物种也可能受到变暖的直接影响。
