Evolutionary Logic is bad logic

A study have recently found that mothers eating a calorie rich diet are more likely to have boys than those of a low calorie diet. In short, high energy diet = boys; low energy diet = girls.

("Mother's Diet Influences Infant Sex: High Energy Intake Linked To Conception Of Sons" at http://www.sciencedaily.com/releases/2008/04/080422194553.htm)

The summary from this, according to Dr. Fiona Mathews:

"Potentially, males of most species can father more offspring than females, but this can be strongly influenced by the size or social status of the male, with poor quality males failing to breed at all. Females, on the other hand, reproduce more consistently. If a mother has plentiful resources then it can make sense to invest in producing a son because he is likely to produce more grandchildren than would a daughter. However, in leaner times having a daughter is a safer bet."

But shouldn't it be the other way around. Since one male can father many children, the specie really only need one male and alot of females. In short, the number of offspring is limited to the number of avialable females. Thus in times of plenty the specie needs alot of females (to give birth) and a few males. In time of scaricity the specie should have few females (which limits the number of births) and many males.