Data from: Geographical variation in the heterogeneity of mutualistic networks

Plant-animal mutualistic networks are characterized by highly heterogeneous degree distributions. The majority of species interact with few partner species, while a small number are highly connected to form network hubs that are proposed to play an important role in community stability. It has not been investigated, however, if or how the degree distributions vary among types of mutualisms or communities, or between plants and animals in the same network. Here, we evaluate the degree distributions of pollination and seed dispersal networks, which are two major types of mutualistic networks that have often been discussed in parallel, using an index based on Pielou’s evenness. Among 56 pollination networks we found strong negative correlation of the heterogeneity between plants and animals, and geographical shifts of network hubs from plants in temperate to animals in tropics. For 28 seed-dispersal networks, in contrast, the correlation was positive, and there is no comparable geographical pattern. These results may be explained by evolution towards specialization in the presence of context-dependent costs that occur if plants share the animal species as interaction partner. How the identity of network hubs affects the stability and resilience of the community is an important question for future studies.

动-植物互利共生网络以高度异质性的度分布为典型特征。绝大多数物种仅与少量伙伴物种发生交互作用，而极少数物种拥有极高连接度，形成网络枢纽（network hubs），这类枢纽被认为在群落稳定性中发挥关键作用。然而，现有研究尚未探明：不同类型的互利共生或不同群落间的度分布是否存在差异，以及同一网络内动植物间的度分布差异规律。本研究基于皮卢均匀度指数（Pielou’s evenness），对两类常被并行讨论的主要互利共生网络——传粉网络与种子传播网络的度分布进行评估。在56个传粉网络中，我们发现动植物间的异质性呈现显著负相关，且网络枢纽的地理分布存在偏移：温带网络的枢纽多为植物，而热带网络的枢纽则多为动物。与之相对，在28个种子传播网络中，二者的相关性为正相关，且未观测到类似的地理分布模式。上述结果可通过以下机制解释：当植物共享同一动物物种作为交互伙伴时，会产生依赖于环境的成本，进而推动物种向特化方向演化。网络枢纽的身份如何影响群落的稳定性与恢复力，是未来研究亟待解答的重要科学问题。