Data from: Why are some plant-pollinator networks more nested than others?

1. Empirical studies have found that the mutualistic interactions forming the structure of plant-pollinator networks are typically more nested than expected by chance alone. Additionally, theoretical studies have shown a positive association between the nested structure of mutualistic networks and community persistence. Yet, it has been shown that some plant-pollinator networks may be more nested than others, raising the interesting question of which factors are responsible for such enhanced nested structure. 2. It has been argued that ordered network structures may increase the persistence of ecological communities under less predictable environments. This suggests that nested structures of plant-pollinator networks could be more advantageous under highly seasonal environments. While several studies have investigated the link between nestedness and various environmental variables, unfortunately, there has been no unified answer to validate these predictions. Here, we move from the problem of describing network structures to the problem of comparing network structures. We develop comparative statistics, and apply them to investigate the association between the nested structure of 59 plant-pollinator networks and the temperature seasonality present in their locations. 3. We demonstrate that higher levels of nestedness are associated with a higher temperature seasonality. We show that the previous lack of agreement came from an extended practice of using standardized measures of nestedness that cannot be compared across different networks. 4. Importantly, our observations complement theory showing that more nested network structures can increase the range of environmental conditions compatible with species coexistence in mutualistic systems, also known as structural stability. This increase in nestedness should be more advantageous and occur more often in locations subject to random environmental perturbations, which could be driven by highly changing or seasonal environments. This synthesis of theory and observations could prove relevant for a better understanding of the ecological processes driving the assembly and persistence of ecological communities.

1. 已有实证研究表明，构成植物-传粉者网络（plant-pollinator networks）结构的互利相互作用（mutualistic interactions），其嵌套程度通常高于随机过程单独作用下的预期水平。此外，理论研究已证实，互利网络的嵌套结构与群落持久性（community persistence）呈正相关关系。然而，部分植物-传粉者网络的嵌套性（nestedness）高于其他网络，这引出了一个颇具研究价值的科学问题：究竟是哪些因素促成了这种增强的嵌套结构？
2. 有研究提出，有序的网络结构可提升生态群落在不可预测环境中的存续能力。这意味着植物-传粉者网络的嵌套结构在高度季节性的环境中可能更具优势。尽管已有多项研究探讨了嵌套性与各类环境变量之间的关联，但目前尚未有统一的结论能够验证上述预测。本研究从描述网络结构的问题转向比较网络结构的问题，我们构建了比较统计量，并将其应用于分析59个植物-传粉者网络的嵌套结构与其所在区域的温度季节性（temperature seasonality）之间的关联。
3. 本研究证实，更高的嵌套性水平与更强的温度季节性呈正相关。同时，我们发现此前研究未能达成统一结论的原因在于，学界长期沿用了无法在不同网络间进行比较的标准化嵌套性度量方法。
4. 尤为关键的是，本研究的观测结果补充了相关理论：在互利系统中，更复杂的嵌套结构可扩大物种共存（species coexistence）所需的环境条件范围，即结构稳定性（structural stability）。这种嵌套性的提升在易受随机环境扰动的区域（如环境剧烈变化或季节性显著的区域）应更具优势，且出现频率更高。本次理论与观测结果的结合，有望为深入理解驱动生态群落组装与存续的生态过程提供新的理论支撑与参考依据。