Data from: Coevolution and the architecture of mutualistic networks

Although coevolution is widely recognized as an important evolutionary process for pairs of reciprocally specialized species, its importance within species-rich communities of generalized species has been questioned. Here we develop and analyze mathematical models of mutualistic communities, such as those between plants and pollinators or plants and seed-dispersers to evaluate the importance of coevolutionary selection within complex communities. Our analyses reveal that coevolutionary selection can drive significant changes in trait distributions with important consequences for the network structure of mutualistic communities. One such consequence is greater connectance caused by an almost invariable increase in the rate of mutualistic interaction within the community. Another important consequence is altered patterns of nestedness. Specifically, interactions mediated by a mechanism of phenotype matching tend to be anti-nested when coevolutionary selection is weak and even more strongly anti-nested as increasing coevolutionary selection favors the emergence of reciprocal specialization. In contrast, interactions mediated by a mechanism of phenotype differences tend to be nested when coevolutionary selection is weak, but less nested as increasing coevolutionary selection favors greater levels of generalization in both plants and animals. Taken together, our results show that coevolutionary selection can be an important force within mutualistic communities, driving changes in trait distributions, interaction rates, and even network structure.

尽管协同进化（coevolution）作为互惠特化的物种种对的重要进化过程已得到广泛认可，但其在物种丰富的泛化物种群落中的重要性却备受质疑。本文构建并分析了互惠群落（mutualistic communities，即植物与传粉者、植物与种子传播者之间的互作群落）的数学模型，以评估协同进化选择在复杂群落中的重要性。我们的分析显示，协同进化选择可显著改变群落内的性状分布，进而对互惠群落的网络结构产生关键影响。其中一类影响为：群落内互惠互作速率近乎恒定提升，由此带来更高的群落连接度。另一项重要影响则是嵌套性（nestedness）的模式发生改变。具体而言，由表型匹配（phenotype matching）机制介导的物种互作，在协同进化选择较弱时往往呈现反嵌套结构；随着协同进化选择强度提升、互惠特化现象逐步显现，其反嵌套程度会进一步加深。与之相反，由表型差异（phenotype differences）机制介导的物种互作，在协同进化选择较弱时通常呈现嵌套结构，但随着协同进化选择增强，动植物双方愈发倾向泛化互作，其嵌套程度会有所降低。综上，本研究结果表明，协同进化选择可成为互惠群落中的重要进化驱动力，推动群落性状分布、互作速率乃至网络结构发生改变。