School of Biological Sciences, Georgia Institute of Technology, Atlanta, GA, USA.
Department of Biology, University of Maryland, College Park, MD, USA.
Nat Commun. 2024 Mar 7;15(1):2105. doi: 10.1038/s41467-024-46165-3.
Photosynthesis fuels primary production at the base of marine food webs. Yet, in many surface ocean ecosystems, diel-driven primary production is tightly coupled to daily loss. This tight coupling raises the question: which top-down drivers predominate in maintaining persistently stable picocyanobacterial populations over longer time scales? Motivated by high-frequency surface water measurements taken in the North Pacific Subtropical Gyre (NPSG), we developed multitrophic models to investigate bottom-up and top-down mechanisms underlying the balanced control of Prochlorococcus populations. We find that incorporating photosynthetic growth with viral- and predator-induced mortality is sufficient to recapitulate daily oscillations of Prochlorococcus abundances with baseline community abundances. In doing so, we infer that grazers in this environment function as the predominant top-down factor despite high standing viral particle densities. The model-data fits also reveal the ecological relevance of light-dependent viral traits and non-canonical factors to cellular loss. Finally, we leverage sensitivity analyses to demonstrate how variation in life history traits across distinct oceanic contexts, including variation in viral adsorption and grazer clearance rates, can transform the quantitative and even qualitative importance of top-down controls in shaping Prochlorococcus population dynamics.
光合作用为海洋食物网的基础提供初级生产力。然而，在许多海洋表面生态系统中，昼夜驱动的初级生产与每日损失紧密耦合。这种紧密的耦合提出了一个问题：在更长的时间尺度上，哪些自上而下的驱动因素在维持持久稳定的微微型蓝藻种群中占主导地位？受北太平洋亚热带环流（NPSG）中高频地表水测量的启发，我们开发了多营养层次模型，以研究底层和上层控制原绿球藻种群平衡的机制。我们发现，将光合作用生长与病毒和捕食者诱导的死亡率结合起来，足以重现原绿球藻丰度的日常波动与基线群落丰度。这样，我们推断在这种环境中，尽管病毒粒子的密度很高，但食草动物仍然是主要的自上而下的因素。模型与数据的拟合也揭示了光依赖性病毒特征和非典型因素对细胞损失的生态相关性。最后，我们利用敏感性分析来证明不同海洋环境中生命史特征的变化，包括病毒吸附和食草动物清除率的变化，如何改变自上而下的控制对原绿球藻种群动态的定量甚至定性影响。
