Data from: Direct and plant trait-mediated effects of the local environmental context on butterfly oviposition patterns

Variation in the intensity of plant-animal interactions over different spatial scales is widespread and might strongly influence fitness and trait selection in plants. Differences in traits among plant individuals have been shown to influence variation in interaction intensities within populations, while differences in environmental factors and community composition are shown to be important for variation over larger scales. However, little is still known about the relative importance of the local environmental context vs. plant traits for the outcome of interactions within plant populations. We investigated how oviposition by the seed-predator butterfly Phengaris alcon on its host plant Gentiana pneumonanthe was related to host plant traits and to local environmental variation, as well as how oviposition patterns translated into effects on host plant fruit set. We considered the local environmental context in terms of height of the surrounding vegetation and abundance of the butterfly’s second host, Myrmica ants. The probability of oviposition was higher in plants that were surrounded by lower vegetation, and both the probability of oviposition and the number of eggs increased in early-flowering and tall plants with many flowers in the three study populations. Flowering phenology, shoot height and flower production were, in turn, related to higher surrounding vegetation. Myrmica abundance was correlated with vegetation height, but had no effect on oviposition patterns. Oviposition and subsequent seed predation by the caterpillars strongly reduced host plant fruit set. Our results show that plant-animal interactions are context-dependent not only because the context influences the abundance or the behavior of the animal interactor, but also because it influences the expression of plant traits that affect the outcome of the interaction. The results also demonstrate that heterogeneity in environmental conditions at a very local scale can be important for the outcomes of interactions.动植物相互作用（plant-animal interactions）强度在不同空间尺度上的变异普遍存在，且可能对植物的适合度（fitness）与性状选择产生强烈影响。已有研究表明，植物个体间的性状差异会影响种群内交互作用强度的变异，而环境因子与群落组成的差异则对更大尺度上的变异具有重要作用。然而，目前对于植物种群内交互作用结果而言，局域环境背景与植物性状的相对重要性仍知之甚少。本研究探究了食籽蝶霾灰蝶（Phengaris alcon）在其寄主植物沼生龙胆（Gentiana pneumonanthe）上的产卵行为与寄主植物性状及局域环境变异的关联，同时分析产卵模式如何转化为对寄主植物坐果率（fruit set）的影响。本研究从周边植被高度与该蝶类第二寄主红蚁属（Myrmica）蚂蚁的种群多度两个维度表征局域环境背景。在周边植被更低矮的植株上，产卵概率更高；在三个研究种群中，开花更早、株高更高且花朵数量更多的植株，其产卵概率与卵粒数均有所提升。反过来，周边植被高度越高，植株的开花物候、株高以及花朵产量均受到显著影响。红蚁属蚂蚁的种群多度与植被高度相关，但对产卵模式并无影响。产卵以及随后幼虫的食籽行为会大幅降低寄主植物的坐果率。本研究结果表明，动植物相互作用具有背景依赖性，这不仅是因为背景会影响交互动物的多度或行为，还因为背景会调控影响交互结果的植物性状表达。本研究结果同时证实，极小尺度下的环境条件异质性对交互作用结果具有重要意义。