Després Laurence, Ibanez Sébastien, Hemborg Asa M, Godelle Bernard
Laboratoire d'Ecologie Alpine, CNRS UMR 5553, Université J. Fourier, BP 53, 38041, Grenoble, France.
Oecologia. 2007 Mar;151(2):240-50. doi: 10.1007/s00442-006-0578-x. Epub 2006 Oct 18.
Interspecific interactions can vary within and among populations and geographic locations, and this variation can influence the nature of the interaction (e.g. mutualistic vs. antagonistic) and its evolutionary stability. Globeflowers are exclusively pollinated by flies, whose larvae feed only on their seeds. Here we document geographic variability in costs and benefits in globeflowers in sustaining their pollinating flies throughout the range of this arctic-alpine European plant over several years. A total of 1,710 flower heads from 38 populations were analysed for their carpel, egg and seed contents. Individual and population analyses control for the confounding influences of variation in both: (1) population traits, such as fly density and egg distribution among flower heads; and (2) individuals traits, such as carpel and egg numbers per flower head. Despite considerable variation in ecological conditions and pollinator densities across populations, large proportions (range 33-58%) of seeds were released after predation, with a benefit-to-cost ratio of 3, indicating that the mutualism is stable over the whole globeflower geographical range. The stability of the mutualistic interaction relies on density-dependent competition among larvae co-developing in a flower head. This competition is revealed by a sharp decrease in the number of seeds eaten per larva with increasing larval number, and is intensified by non-uniform egg distribution among globeflowers within a population. Carpel number is highly variable across globeflowers (range 10-69), and flies lay more eggs in large flowers. Most plants within a population contribute to the rearing of pollinators, but the costs are greater for some than for others. Large globeflowers lose more seed to pollinator larvae, but also release more seed than smaller plants. The apparent alignment of interests between fly and plants (positive relationship between numbers of seed released and destroyed) is shown to hide a conflict of interest found when flower size is controlled for.
种间相互作用在种群内部、种群之间以及不同地理位置可能会有所不同，这种变化会影响相互作用的性质（例如互利共生与拮抗作用）及其进化稳定性。金莲花完全由苍蝇授粉，而苍蝇的幼虫仅以其种子为食。在此，我们记录了多年来在这种北极 - 高山欧洲植物的整个分布范围内，金莲花在维持其授粉苍蝇方面成本和收益的地理变异性。对来自38个种群的总共1710个花头的心皮、卵和种子含量进行了分析。个体和种群分析控制了以下两方面变异的混杂影响：（1）种群特征，如苍蝇密度和花头之间的卵分布；（2）个体特征，如花头的心皮数和卵数。尽管不同种群的生态条件和传粉者密度存在相当大的差异，但很大比例（范围为33% - 58%）的种子在被捕食后仍被释放，收益成本比为3，这表明这种互利共生关系在金莲花的整个地理分布范围内是稳定的。互利共生相互作用的稳定性依赖于在一个花头中共同发育的幼虫之间的密度依赖性竞争。随着幼虫数量的增加，每个幼虫吃掉的种子数量急剧减少，这揭示了这种竞争，并且种群内金莲花之间卵分布不均匀会加剧这种竞争。金莲花的心皮数变化很大（范围为10 - 69），苍蝇会在大花中产更多的卵。一个种群中的大多数植物都有助于传粉者的养育，但有些植物的成本比其他植物更高。大金莲花因传粉者幼虫而损失的种子更多，但也比小金莲花释放更多的种子。当控制花的大小后发现，苍蝇和植物之间明显的利益一致性（释放和被破坏的种子数量之间的正相关关系）隐藏了利益冲突。
