Data from: Resilient networks of ant-plant mutualists in Amazonian forest fragments

BACKGROUND: The organization of networks of interacting species, such as plants and animals engaged in mutualisms, strongly influences the ecology and evolution of partner communities. Habitat fragmentation is a globally pervasive form of spatial heterogeneity that could profoundly impact the structure of mutualist networks. This is particularly true for biodiversity-rich tropical ecosystems, where the majority of plant species depend on mutualisms with animals and it is thought that changes in the structure of mutualist networks could lead to cascades of extinctions. METHODOLOGY/PRINCIPAL FINDINGS: We evaluated effects of fragmentation on mutualistic networks by calculating metrics of network structure for ant-plant networks in continuous Amazonian forests with those in forest fragments. We hypothesized that networks in fragments would have fewer species and higher connectance, but equal nestedness and resilience compared to forest networks. Only one of the nine metrics we compared differed between continuous forest and forest fragments, indicating that networks were resistant to the biotic and abiotic changes that accompany fragmentation. This is partially the result of the loss of only specialist species with one connection that were lost in forest fragments. CONCLUSIONS/SIGNIFICANCE: We found that the networks of ant-plant mutualists in twenty-five year old fragments are similar to those in continuous forest, suggesting these interactions are resistant to the detrimental changes associated with habitat fragmentation, at least in landscapes that are a mosaic of fragments, regenerating forests, and pastures. However, ant-plant mutualistic networks may have several properties that may promote their persistence in fragmented landscapes. Proactive identification of key mutualist partners may be necessary to focus conservation efforts on the interactions that insure the integrity of network structure and the ecosystems services networks provide.背景： 物种互作网络（如参与互利共生（mutualism）的动植物）的组织方式，可深刻影响共生伙伴群落的生态学特征与演化进程。生境破碎化（habitat fragmentation）是一种全球广泛分布的空间异质性形式，能够对互利共生网络的结构产生深远影响，这一点在生物多样性富集的热带生态系统中尤为显著——该类生态系统中绝大多数植物物种依赖与动物的互利共生关系，且学界普遍认为，互利共生网络结构的改变可能引发灭绝级联效应。 方法与主要发现： 本研究通过对比亚马逊连续林与森林片段中蚁-植物（ant-plant）互利共生网络的结构指标，评估了生境破碎化对互利共生网络的影响。我们提出假设：相较于连续林内的共生网络，片段林内的网络物种数更少、连接度（connectance）更高，但嵌套性（nestedness）与恢复韧性（resilience）与之相当。在我们对比的9项指标中，仅1项在连续林与森林片段间存在显著差异，表明共生网络对伴随破碎化出现的生物与非生物改变具有抗性。这一结果的部分成因是，森林片段中仅丢失了仅具有单一连接的特化物种。 结论与意义： 本研究发现，形成时长25年的森林片段中的蚁-植物互利共生网络，与连续林内的网络结构相似，这表明此类互作关系对生境破碎化带来的有害改变具有抗性，至少在由破碎化林块、恢复林与牧场构成的景观中是如此。不过，蚁-植物互利共生网络可能具备多种可促进其在破碎化景观中存续的特性。为了将保护工作聚焦于能够保障网络结构完整性及其所提供生态系统服务的互作关系，主动识别关键共生伙伴或属必要之举。