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.

传粉者对花卉密度的响应，对植物生物学具有重要意义。具体而言，低密度条件下传粉者访问量的下降可引发植物种群出现阿利效应（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。已有实证研究者报道了花卉或植物密度与传粉者访问率之间的多种关联模式。本文构建并验证了一个可解释该多样性的理论模型。该模型假设：传粉者会在焦点花卉斑块与周边环境之间分配自身的觅食活动，以最大化觅食成功率。由此推导得到的单花访问率与焦点斑块花卉密度的关联呈非线性特征：在低花卉密度下呈现正向效应，而在较高密度下效应减弱或转为负向。该关联模式同时受周边环境的花卉密度、以及植物与传粉者双方的功能性状的影响。在一项野外实验中，Holocarpha virgata ssp. virgata的花卉密度对单花访问率具有非线性影响，这一结果与模型的预测基本一致。本模型基于生物学合理的假设提出了可验证的假说，可为解释植物-传粉者互利共生的重要方面提供基础研究起点。