Data from: Stability and generalization in seed dispersal networks: a case study of frugivorous fish in Neotropical wetlands

When species within guilds perform similar ecological roles, functional redundancy can buffer ecosystems against species loss. Using data on the frequency of interactions between fish and fruit, we assessed whether co-occurring frugivores provide redundant seed dispersal services in three species-rich Neotropical wetlands. Our study revealed that frugivorous fishes have generalized diets; however, large-bodied fishes had greater seed dispersal breadth than small species, in some cases, providing seed dispersal services not achieved by smaller fish species. As overfishing disproportionately affects big fishes, the extirpation of these species could cause larger secondary extinctions of plant species than the loss of small specialist frugivores. To evaluate the consequences of frugivore specialization for network stability, we extracted data from 39 published seed dispersal networks of frugivorous birds, mammals and fish (our networks) across ecosystems. Our analysis of interaction frequencies revealed low frugivore specialization and lower nestedness than analyses based on binary data (presence–absence of interactions). In that case, ecosystems may be resilient to loss of any given frugivore. However, robustness to frugivore extinction declines with specialization, such that networks composed primarily of specialist frugivores are highly susceptible to the loss of generalists. In contrast with analyses of binary data, recently developed algorithms capable of modelling interaction strengths provide opportunities to enhance our understanding of complex ecological networks by accounting for heterogeneity of frugivore–fruit interactions.

当功能群（guilds）内的物种承担相似的生态角色时，功能冗余（functional redundancy）可缓冲生态系统，抵御物种丧失带来的负面影响。本研究借助鱼类与果实间的互作频率数据，评估了3个物种丰富的新热带湿地中，共存的食果动物是否能够提供冗余的种子传播服务。
研究结果显示，食果性鱼类拥有泛化食谱；但体型较大的鱼类相较于小型物种，具备更广的种子传播广度，在部分场景下可提供小型鱼类无法实现的种子传播服务。由于过度捕捞对大型鱼类的影响不成比例，相较于丧失小型特食性食果动物，这类大型物种的灭绝可能引发更大规模的植物次级灭绝事件。
为评估食果动物特化程度对互作网络稳定性的影响，我们从覆盖多种生态系统的39份已发表的食果鸟类、哺乳类及鱼类种子传播互作网络（本研究数据集网络）中提取了相关数据。针对互作频率的分析显示，相较基于二元数据（binary data，即互作的存在-缺失情况）的分析，本研究中的食果动物特化程度更低，嵌套性（nestedness）也更弱。在此情形下，生态系统对任意单一食果动物的丧失均具备恢复力。然而，食果动物灭绝的鲁棒性会随特化程度提升而下降，即主要由特食性食果动物构成的网络，对泛化物种（generalists）的丧失高度易感。
与二元数据分析方法不同，新近开发的可建模互作强度的算法，通过考量食果动物-果实互作的异质性，为我们深入理解复杂生态网络提供了新的研究路径。