Patterns of reproductive effort in male and female shrubs of Oemleria cerasiformis: a 6-year study

1 We monitored flowering and fruiting of individual male and female plants of Oemleria cerasiformis over a 6-year period in a population in western Canada, and calculated fruit set (percentage of pistils maturing) and reproductive effort (RE) (gram of reproductive tissue per gram of leaf).
2 Over 6 years, male O. cerasiformis had on average much lower total RE, but much higher RE at flowering, than females.
3 In males, strong correlations between RE and light suggested that investment in reproduction was largely determined by light levels. There were strong positive correlations of RE between years, with no evidence of periodic fluctuations.
4 In females, in contrast to males, RE at flowering was not related to light. However, fruit set was strongly correlated with light. Flowering RE and fruit set were uncorrelated in females, indicating that these are affected by different factors.
5 Correlations of RE between years in females, although often significant, were lower than in males, indicating that RE fluctuates more between years in females than in males and may respond to past levels of RE. Flowering may reflect adjustments in response to past reproduction, or may be controlled by resources other than light. Fruit set was not significantly related to previous RE.
6 The greater total RE of females and their limited ability to adjust fruit set are probably major factors contributing to the greater mortality rates of females and the male-biased sex ratios in O. cerasiformis .