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 nests, 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. By 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，因为相互作用中的部分成员会以牺牲其他成员为代价，获得更高的适合度收益。我们针对南非一处疑似鸟-植物互利共生关系提供了详细的自然历史数据：当地多种鸟类利用Eriocephalus属（Eriocephalus）植物的种子绒毛搭建巢穴，理论上可协助该植物完成种子传播。本研究聚焦于一种常见鸣禽——斑鹪莺（Prinia maculosa），该物种会投入大量精力收集Eriocephalus属植物的筑巢材料。斑鹪莺的筑巢周期中位数为6天，其中会花费5天时间向巢穴中添加种子绒毛材料，且经常飞出自身领地边界以收集Eriocephalus属植物的绒毛。然而，斑鹪莺主要收集的是Eriocephalus属植物的绒毛，会主动避开收集种子。平均每个斑鹪莺巢穴仅含6.6颗种子，但却包含来自579颗种子的绒毛。上述数据表明，斑鹪莺能为Eriocephalus属植物提供的种子传播收益十分有限。与之形成鲜明对比的是，斑鹪莺巢穴中大量的Eriocephalus属植物绒毛，以及其为收集该材料所投入的精力，均说明使用Eriocephalus属材料搭建巢穴能为斑鹪莺带来显著收益。本研究最后将提出若干假说，以阐释Eriocephalus属植物材料可为斑鹪莺及其他鸟类提供的潜在适合度收益。