Department of Civil and Environmental Engineering, MIT, Cambridge, MA, USA.
Department of Biology, Ecology and Evolution, University of Fribourg, Fribourg, Switzerland.
J Anim Ecol. 2017 Oct;86(6):1417-1424. doi: 10.1111/1365-2656.12749. Epub 2017 Sep 28.
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. 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. 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. 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.
实证研究发现，形成植物-传粉者网络结构的互利相互作用通常比仅靠机会形成的相互作用更为嵌套。此外，理论研究表明，互利网络的嵌套结构与群落持久性之间存在正相关关系。然而，已经表明，一些植物-传粉者网络可能比其他网络更具嵌套性，这就提出了一个有趣的问题，即哪些因素导致了这种增强的嵌套结构。有人认为，有序的网络结构可以在环境变化较大的情况下提高生态群落的持久性。这表明，植物-传粉者网络的嵌套结构在高度季节性的环境下可能更具优势。尽管有几项研究调查了嵌套性与各种环境变量之间的联系，但遗憾的是，目前还没有一个统一的答案来验证这些预测。在这里，我们从描述网络结构的问题转向比较网络结构的问题。我们开发了比较统计学，并将其应用于调查 59 个植物-传粉者网络的嵌套结构与它们所在位置的温度季节性之间的关联。我们证明，更高水平的嵌套性与更高的温度季节性相关。我们表明，以前缺乏一致性是由于广泛使用标准化的嵌套性度量标准，这些标准不能在不同的网络之间进行比较。重要的是，我们的观察结果补充了理论，表明更嵌套的网络结构可以增加在互利系统中物种共存兼容的环境条件范围，也称为结构稳定性。这种嵌套性的增加在受到随机环境干扰的地方应该更有利，也更常见，这些干扰可能是由变化剧烈或季节性的环境驱动的。这种理论和观察的综合可以证明对于更好地理解驱动生态群落组装和持久性的生态过程是相关的。
