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.研究背景：参与互利共生（mutualism）的动植物等相互作用物种的网络组织，对共生伙伴群落的生态学与进化过程具有显著调控作用。生境破碎化（habitat fragmentation）是一种全球广泛分布的空间异质性（spatial heterogeneity）形式，可深刻改变互利共生网络（mutualistic network）的结构。这一点在生物多样性丰富的热带生态系统中尤为突出：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互作，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。 研究方法与主要发现：本研究通过计算亚马孙连续森林与森林片段生境中蚁-植物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。我们提出如下假说：与连续森林中的网络相比，片段生境中的网络物种丰富度更低、连接度（connectance）更高，但嵌套性（nestedness）与恢复力（resilience）与之相当。最终，在我们对比的9项指标中，仅1项在连续森林与片段生境的网络间存在显著差异，表明此类网络对伴随生境破碎化出现的生物与非生物变化具有抗性。这一结果部分源于片段生境中仅丢失了仅具有单一联结的特化物种（specialist species）。 结论与意义：本研究发现，25年生的森林片段中的蚁-植物互利共生网络与连续森林中的同类网络结构相似，表明这些种间互作对生境破碎化带来的有害变化具有抗性——至少在由片段生境、恢复林与牧场构成的镶嵌式景观中是如此。不过，蚁-植物互利共生网络可能具备若干可促进其在破碎化景观中存续的特性。若要将保育工作聚焦于保障网络结构完整性及其所提供的生态系统服务（ecosystem services）的互作关系，主动识别关键互利共生伙伴或许是必要的。