Floral density and co-occurring congeners alter patterns of selection in annual plant communities

While the evolution and diversification of flowers is often attributed to pollinator-mediated selection, interactions between co-occurring plant species can alter patterns of selection mediated by pollinators and other agents. The extent to which both floral density and congeneric species richness affect patterns of net and pollinator-mediated selection on multiple co-occurring species in a community is unknown and is likely to depend on whether co-occurring plants experience competition or facilitation for reproduction. We conducted an observational study of selection on four species of Clarkia (Onagraceae) and tested for pollinator-mediated selection on two Clarkia species in communities differing in congeneric species richness and local floral density. When selection varied with community context, selection was generally stronger in communities with fewer species, where local conspecific floral density was higher, and where local heterospecific floral density was lower. These patterns suggest that intraspecific competition at high densities and interspecific competition at low densities may affect the evolution of floral traits. However, selection on floral traits was not pollinator-mediated in C. cylindrica or C. xantiana, despite variation in pollinator visitation and the extent of pollen limitation across communities for C. cylindrica. As such, interactions between co-occurring species may alter patterns of selection mediated by abiotic agents of selection.
Methods
All procedures for data collection and processing are listed in the manuscript. The units for each variable are in the datadescriptors.csv file.

尽管花卉的演化与多样化通常被归因于传粉者介导的选择（pollinator-mediated selection），但同域共存的植物物种间的相互作用，能够改变传粉者与其他作用因子所介导的选择模式。目前尚不清楚，在一个群落中，花卉密度以及同属物种丰富度（congeneric species richness）究竟会在多大程度上影响多个共生物种的净选择（net selection）模式与传粉者介导的选择，且这一影响程度大概率取决于共生物种在繁殖过程中是经历竞争还是促进作用。我们针对克拉克花属（Clarkia）的4个物种（柳叶菜科Onagraceae）开展了选择效应的观测研究，并在同属物种丰富度与局域花卉密度（local floral density）存在差异的群落中，检验了2个克拉克花属物种的传粉者介导选择。当选择效应随群落背景发生变化时，其通常在物种更少、局域同种花卉密度更高、局域异种花卉密度更低的群落中表现得更强。上述模式表明，高密度下的种内竞争（intraspecific competition）与低密度下的种间竞争（interspecific competition），或许会影响花卉性状的演化。然而，尽管不同群落间的传粉者访花频率与C. cylindrica的花粉限制（pollen limitation）程度存在差异，但C. cylindrica与C. xantiana的花卉性状选择并未受到传粉者介导。由此可见，共生物种间的相互作用或许会改变非生物选择因子（abiotic agents of selection）所介导的选择模式。
方法
所有数据采集与处理流程均已在论文手稿中列明。各变量的单位详见datadescriptors.csv文件。