Rarity of microalgae in macro, meso, and microhabitats

Climate change and human-induced habitat degradations result in loss of species diversity in natural ecosystems. While the extinction of macroscopic organisms has been well documented in the scientific literature and public media, we have only limited knowledge on the loss of microscopic elements of the ecosystems. Because rarity coincides with the increased risk of extinction, we investigated the commonness and rarity of microalgae in the Pannonian ecoregion. We reviewed the published literature of microalgal research in Hungary over the last 140 years and created a species-by-site matrix containing 2489 algae species and 1145 localities. Analysing this dataset, we found that although the core-satellite hypothesis suggests a bimodal site occupancy distribution, microalgae displayed a unimodal pattern with a high number of rarely occurring species. We also demonstrated that the well-known negative relationship between body size of organisms and number of occupied habitats holds for microalgae. Rarity values of taxa have a phylogenetic signal indicating that in terms of rarity, closely related species (desmids, dinoflagellates, euglenophytes) show considerable similarities. The various habitat types showed differences in the number of rare taxa. Small- and medium-sized habitats (bog lakes, streams, oxbows) hosted the majority of rare species. These results highlight the conservation importance of small habitats in preserving microbial diversity.气候变化与人类活动引发的生境退化，导致自然生态系统的物种多样性丧失。尽管大型生物的灭绝在科学文献与公共媒体中已有充分记载，但我们对生态系统中微型生物类群的丧失却知之甚少。鉴于稀有性与灭绝风险升高呈正相关，我们针对潘诺尼亚生态区（Pannonian ecoregion）内微藻的常见性与稀有性展开了调查。我们梳理了过去140年间匈牙利境内有关微藻研究的已发表文献，构建了包含2489个藻类物种与1145个样地的物种-样地矩阵。通过对该数据集的分析，我们发现：尽管核心-卫星假说（core-satellite hypothesis）预测样地占有分布应呈双峰模式，但微藻却呈现出单峰格局，且包含大量稀有种。我们还证实，生物体型与占据生境数量之间的公认负相关关系，同样适用于微藻类群。类群的稀有性数值存在系统发育信号，这表明在稀有性层面，亲缘关系相近的物种（鼓藻类（desmids）、甲藻类（dinoflagellates）与裸藻类（euglenophytes））展现出显著的相似性。不同生境类型的稀有类群数量存在差异。中小型生境（泥炭湖、溪流与牛轭湖）承载了绝大多数稀有物种。上述研究结果凸显了小型生境在保护微生物多样性方面的重要保育价值。