Stratton Donald A
Department of Ecology and Evolution, State University of New York, Stony Brook, NY, 11794, USA.
Evolution. 1992 Feb;46(1):92-106. doi: 10.1111/j.1558-5646.1992.tb01987.x.
The magnitude and direction of phenotypic selection on emergence date and seedling size in Erigeron annuus was measured to determine the heterogeneity of selection among sites and the proportion of fitness variance explained by seedling size and emergence date. Three disturbance treatments (open, annual vegetation, perennial vegetation) were imposed to test the hypothesis of stronger selection on seedlings in competitive environments. Selection was most heterogeneous early in the life cycle, with significant spatial heterogeneity in the magnitude of selection on a local scale. The disturbance treatments affected only fecundity selection gradients and selection was strongest in open plots. Significant variation in the sign of selection differentials on emergence date was observed for establishment and fall viability selection episodes; at later stages selection varied in magnitude but not direction. Seedlings in the earliest cohort experienced high mortality during establishment, but increased size and fecundity later in the life cycle. Both stabilizing and disruptive selection on emergence date were observed during establishment, but in general selection was purely directional. At Stony Brook most selection on emergence date operated indirectly through seedling size, whereas at the Weld Preserve direct selection was stronger. There were persistent effects of both seedling emergence date and rosette diameter on adult fitness components, and October rosette diameter explained 18% of the total phenotypic variance in fecundity. Overall, viability fitness components were much more important than fecundity selection. Winter survivorship was the single most important episode of selection.
为了确定不同地点间选择的异质性以及由幼苗大小和出苗日期所解释的适合度方差比例，对一年蓬出苗日期和幼苗大小的表型选择强度及方向进行了测定。设置了三种干扰处理（开阔地、一年生植被、多年生植被），以检验在竞争环境中对幼苗选择更强这一假设。选择在生命周期早期最为异质，在局部尺度上选择强度存在显著的空间异质性。干扰处理仅影响繁殖力选择梯度，且在开阔地块中选择最强。在定植和秋季存活力选择阶段，观察到出苗日期选择差的符号存在显著变化；在后期阶段，选择强度有所不同，但方向不变。最早一批幼苗在定植期间死亡率很高，但在生命周期后期大小和繁殖力增加。在定植期间观察到对出苗日期既有稳定选择也有分裂选择，但总体而言选择是纯粹定向的。在石溪，对出苗日期的大多数选择是通过幼苗大小间接起作用的，而在韦尔德保护区直接选择更强。幼苗出苗日期和莲座直径对成体适合度成分都有持续影响，10月莲座直径解释了繁殖力总表型方差的18%。总体而言，存活力适合度成分比繁殖力选择重要得多。冬季存活率是最重要的单一选择阶段。
