Data from: Explaining variation in the effect of floral density on pollinator visitation

Pollinator responses to floral density have important implications for plant biology. In particular, a decline in pollinator visitation at low density can cause an Allee effect (a positive relation of fitness to density) in the plant population, which heightens that population's vulnerability to extinction. Empiricists have reported a variety of relations between flower or plant density and pollinator visitation rates. Here I develop and test a model that provides explanations for this diversity. The model assumes that pollinators distribute themselves between a focal patch of flowers and the surrounding environment so as to maximize foraging success. The resulting relation of per-flower visitation rate to focal patch floral density is non-linear, with positive effects at low floral densities and weaker or negative effects at higher densities. The relation is influenced by floral density in the surrounding environment and traits of both the plants and their pollinators. In a field experiment, floral density of Holocarpha virgata ssp. virgata had a non-linear effect on per-flower visitation that was largely consistent with the model's predictions. By producing testable hypotheses based on biologically reasonable assumptions, this model serves as a starting point for explaining an important facet of plant-pollinator mutualisms.

传粉者对花密度的响应对植物生物学研究具有重要意义。具体而言，低密度条件下传粉者访问量的减少，可在植物种群中诱发阿利效应（Allee effect，即适合度与种群密度呈正相关关系），进而加剧该种群的灭绝风险。已有实证研究报道了花或植物密度与传粉者访问率之间的多种关联模式。本文构建并检验了一个可解释该多样性的理论模型。该模型假设传粉者会在焦点花斑块与周边环境间分配其觅食活动，以实现觅食成功率的最大化。由此推导得到的单花访问率与焦点斑块花密度的关系呈非线性特征：在低花密度区间呈现正向效应，而在较高密度区间效应会减弱甚至转为负向。该关联模式受周边环境的花密度、植物自身及其传粉者的功能性状共同调控。田间试验结果表明，纤细黄金杯原亚种（Holocarpha virgata ssp. virgata）的花密度对单花访问率具有非线性影响，该结果与模型的预测大体一致。本模型基于符合生物学逻辑的合理假设生成可检验的假说，可为解释植物-传粉者互利共生的重要方面提供研究起点。