Data from: Fluff-thieving birds sabotage seed dispersal

Characterizing many species interactions as mutualisms can be misleading because some members of the interaction derive greater fitness benefits at the expense of other members. We provide detailed natural history data on a suspected bird-plant mutualism in South Africa where many species of birds use fluffy Eriocephalus seed material to construct their nest, potentially dispersing seeds for the plant. We focus on a common bird, Prinia maculosa, which invests heavily in gathering Eriocephalus material. Prinias spent 5 of their median 6-day nest construction period adding seed material to their nests and frequently travelled outside their territory boundary to gather Eriocephalus material. Yet, prinias gathered primarily Eriocephalus fluff and actively avoided gathering seeds. The average prinia nest contained only 6.6 seeds, but contained fluff from 579 seeds. These data suggest that prinias provide limited dispersal benefits to Eriocephalus plants. In contrast, the large amounts of Eriocephalus fluff in prinia nests, and the effort that prinias invest in gathering it, suggest that prinias benefit from constructing their nests with Eriocephalus material. We end by outlining hypotheses for possible fitness benefits that Eriocephalus material could provide prinias and other birds.

将诸多物种间的相互作用界定为互利共生（mutualism）可能存在误导性，因为此类相互作用中的部分成员会以牺牲其他成员为代价，获取更高的适合度收益。我们针对南非一处疑似鸟类-植物互利共生的场景，提供了详尽的自然历史数据：当地多种鸟类会借助蓬松的Eriocephalus种子材料构筑巢穴，该行为或可帮助该植物完成种子传播。我们将研究重点聚焦于一种常见鸟类——斑鹪莺（Prinia maculosa），该物种会大量收集Eriocephalus材料。斑鹪莺的筑巢周期中位数为6天，其中会花费5天时间向巢内添加种子材料，且时常越出自身领地边界以收集Eriocephalus材料。然而，斑鹪莺主要采集的是Eriocephalus的种絮，且会主动避开种子。单个斑鹪莺巢穴平均仅含6.6颗种子，但却带有来自579颗种子的种絮。上述数据表明，斑鹪莺仅能为Eriocephalus植物带来有限的种子传播收益。与之形成鲜明对比的是，斑鹪莺巢穴中大量存在的Eriocephalus种絮，以及该物种为收集材料所投入的大量精力，均显示出斑鹪莺可通过使用Eriocephalus材料构筑巢穴而获益。我们在文末提出了若干假说，以阐释Eriocephalus材料可为斑鹪莺及其他鸟类带来的潜在适合度收益。