Is there such a thing as a pollen dearth ?
Sure - that's why they store it. But, luckily pollen doesn't only come from seasonal flowers - pollen can be sourced from trees, hedges, and even from grass - ask any hay-fever sufferer !
There was a rather interesting 2010 Hungarian study in which the mineral content of pollen from sunflowers and willow was compared with pollen collected by honey-bees within that immediate area - which may be of some interest:
The following are figures given for mineral content (determined by atomic absorption spectroscopy), flower-pollen first, honeybee-collected pollen second (mg/kg):
Potassium: 7294.70 vs 4334.17
Calcium: 5492.78 vs 2020.23
Magnesium: 1764.86 vs 692.61
Zinc: 75.01 vs 35.83
Iron is a special case, with an unexceptional 325.29 vs 122.87 for willow, but a huge dilution of 2872.89 vs 27.42 for sunflowers. From studies conducted in other countries there appears to be little consensus regarding the normal range of honeybee pollen iron content - it varies wildly.
So it seems that honeybees are diluting mineral-rich pollens with (lower-grade ?) pollen from other sources. Make of that what you will.
LJ