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）作为互惠特化物种种对的重要进化过程已得到广泛认可，但在由泛化物种构成的物种丰富群落中，其重要性却备受质疑。本研究构建并分析了互利共生群落（mutualistic community）的数学模型——例如植物与传粉者（pollinator）、植物与种子传播者（seed-disperser）之间的互利群落——以评估复杂群落内协同进化选择的重要性。我们的分析结果表明，协同进化选择可显著改变群落的性状分布（trait distribution），并对互利共生群落的网络结构产生重要影响。其中一项影响是群落内互利交互速率近乎恒定的提升，进而带来更高的群落连接度（connectance）。另一项重要影响则是嵌套性（nestedness）模式的改变。具体而言，当协同进化选择较弱时，由表型匹配（phenotype matching）机制介导的交互往往呈现反嵌套（anti-nested）特征；随着协同进化选择强度增加，互惠特化逐渐形成，反嵌套特征会愈发显著。与之相反，由表型差异（phenotype difference）机制介导的交互在协同进化选择较弱时通常呈现嵌套特征，但随着协同进化选择强度提升，动植物双方均倾向于更高水平的泛化（generalization），此时嵌套性会随之降低。综合来看，我们的研究结果证实，协同进化选择可作为互利共生群落内的重要进化动力，推动性状分布、交互速率乃至群落网络结构发生改变。