Connectivity loss in experimental pond networks leads to biodiversity loss in microbial metacommunities

Habitat fragmentation is among the most important global threats to biodiversity, however, the direct effects of its components including connectivity loss are largely unknown and still mostly inferred based on indirect evidence. Our understanding of these drivers is especially limited in microbial communities. Here, by conducting a four-month outdoor experiment with artificial pond (mesocosm) metacommunities, we studied the effects of connectivity loss on planktonic microorganisms, primarily focusing on pro- and microeukaryotes. Connectivity loss was simulated by stopping the dispersal among local habitats after an initial period with dispersal. Keeping the habitat amount constant and the abiotic environment homogeneous. allowed us to track the direct effects of the process of connectivity loss. We found that connectivity loss led to higher levels of extinction and a decrease in both local and regional diversity in microeukaryotes. In contrast, diversity patterns of prokaryotes remained largely unaffected, with some indications of extinction debt. Connectivity loss also led to lower evenness in microeukaryotes, likely through changes in biotic interactions with zooplankton grazers. Our results imply that connectivity loss can directly translate into species losses in communities and highlight the importance of conserving habitat networks with sufficient dispersal among local habitats.

生境破碎化是全球范围内对生物多样性最为重要的威胁之一，然而其组分（包括连通性丧失）的直接效应在很大程度上仍未明确，且大多仅能基于间接证据推演得出。我们对这些驱动因子的认知，在微生物群落中尤为匮乏。本研究依托一项为期四个月的人工池塘（中宇宙实验系统，mesocosm）集合群落（metacommunities）野外实验，探究了连通性丧失对浮游微生物的影响，重点关注原核生物（prokaryotes）与微真核生物（microeukaryotes）。连通性丧失的模拟方案为：在初始扩散阶段结束后，阻断局域生境间的扩散过程，同时保持生境总量恒定、非生物环境均质，以此精准追踪连通性丧失过程的直接效应。研究结果显示，连通性丧失会提升微真核生物的灭绝发生率，并降低其局域与区域多样性水平。与之形成鲜明对比的是，原核生物的多样性模式基本未受影响，仅存在部分与灭绝债务（extinction debt）相关的迹象。连通性丧失还会降低微真核生物的群落均匀度，这一现象可能由其与浮游动物牧食者间的生物互作改变所介导。本研究结果表明，连通性丧失可直接导致群落物种丧失，同时凸显了维持局域生境间具备充足扩散能力的生境网络的保护重要性。