Hard and soft selection on phenology through seasonal shifts in the general and social environments: a study on plant emergence time

The timing of transition out of one life history phase determines where in the seasonal succession of environments the next phase is spent. Shifts in the general environment (e.g., seasonal climate) affect the expected fitness for particular transition dates. Variation in transition date also leads to temporal variation in the social environment. For instance, early transition may confer a competitive advantage over later individuals. If so, the social environment will impose frequency- and density-dependent selection components. In effect, the general environment imposes hard selection while the social environment imposes soft selection on phenology. We examined hard and soft selection on seedling emergence time in an experiment on Brassica rapa. In monoculture (uniform social environment), early emergence results in up to a 1.5-fold increase in seed production. In bi-cultures (heterogeneous social environment), early-emerging plants capitalized on their head start, suppressing their l...

生物从某一生活史阶段（life history phase）过渡的时机，决定了其下一阶段所处的环境季节演替序列中的位置。一般环境（如季节性气候）的变化，会影响特定过渡日期下的预期适合度（fitness）。过渡日期的变异同样会引发社会环境（social environment）的时间变异。例如，较早完成过渡的个体相较于较晚个体，可获得竞争优势。若果真如此，社会环境便会施加频率依赖与密度依赖选择（frequency- and density-dependent selection）组分。实际上，一般环境对物候（phenology）施加硬选择（hard selection），而社会环境则施加软选择（soft selection）。我们以芸薹（Brassica rapa）为实验材料，探究了幼苗出苗时间（seedling emergence time）所面临的硬选择与软选择。在单种培养（monoculture，均匀社会环境）条件下，提早出苗可使种子产量最高提升1.5倍。在双种培养（bi-cultures，异质社会环境）条件下，提早出苗的植株可利用其先发优势，抑制其……