Després Laurence, Ibanez Sébastien, Hemborg Asa M, Godelle Bernard
Laboratoire d'Ecologie Alpine, Université J. Fourier, CNRS UMR 5553, BP 53, 38041 Grenoble, France.
Oecologia. 2007 Aug;153(1):69-79. doi: 10.1007/s00442-007-0705-3. Epub 2007 Mar 21.
Interspecific interactions can vary within and among populations and geographical locations, and this variation can influence the nature of the interaction (e.g. mutualistic versus antagonistic) and its evolutionary stability. Globeflowers are exclusively pollinated by flies whose larvae feed only on their seeds. Here we document geographical 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 are 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 some pay more than 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 plant (positive relationship between numbers of seeds 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、种群之间以及地理位置之间可能会有所不同，这种变化会影响相互作用的性质（例如互利共生与拮抗）及其进化稳定性。金莲花仅由蝇类授粉，而蝇类幼虫仅以其种子为食。在这里，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蝇类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，如蝇类密度和花头间的卵分布；（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能释放，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。这种竞争表现为随着幼虫数量增加，每个幼虫吃掉的种子数量急剧减少，并且由于种群内金莲花之间卵分布不均匀而加剧。金莲花的心皮数差异很大（范围为10 - 69），蝇类在大花中产卵更多。一个种群中的大多数植物都为传粉者的养育做出贡献，但有些贡献更多。大金莲花因传粉者幼虫损失的种子更多，但也比小金莲花释放更多的种子。蝇类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）在控制花大小后显示出隐藏的利益冲突。
