Q1.
What is the approximate success rate of the common strategies — wind pollination and insect pollination — with respect to the seed formation?
Answer
Measured as seeds formed per pollen grain released, wind pollination succeeds about once in 6,000 grains and insect pollination about once in 33 grains — insect pollination is roughly 180 times more efficient per grain. The figures come straight from Table 11.3.
success rate = seeds formed ÷ pollen grains released
Wind (maize, wheat): mid-values → pollen = (5,00,000 + 10,00,000) ÷ 2 = 7,50,000; seeds = (50 + 200) ÷ 2 = 125
success rate = 125 ÷ 7,50,000 = 1.7 × 10−4 = 0.017%, i.e. about 1 seed per 6,000 grains
Insect (sunflower): mid-values → pollen = (20,000 + 40,000) ÷ 2 = 30,000; seeds = (800 + 1,000) ÷ 2 = 900
success rate = 900 ÷ 30,000 = 3.0 × 10−2 = 3.0%, i.e. about 1 seed per 33 grains
ratio of efficiencies = 3.0% ÷ 0.017% ≈ 180 times
Wind (maize, wheat): mid-values → pollen = (5,00,000 + 10,00,000) ÷ 2 = 7,50,000; seeds = (50 + 200) ÷ 2 = 125
success rate = 125 ÷ 7,50,000 = 1.7 × 10−4 = 0.017%, i.e. about 1 seed per 6,000 grains
Insect (sunflower): mid-values → pollen = (20,000 + 40,000) ÷ 2 = 30,000; seeds = (800 + 1,000) ÷ 2 = 900
success rate = 900 ÷ 30,000 = 3.0 × 10−2 = 3.0%, i.e. about 1 seed per 33 grains
ratio of efficiencies = 3.0% ÷ 0.017% ≈ 180 times
Why wind is so wasteful: the wind does not know where it is going. A grain released from a wheat anther travels wherever the air happens to move; the chance that it lands on a stigma of its own species is tiny. An insect, in contrast, visits one kind of flower after another of the same kind, because that is where it has learnt the nectar is — so the pollen stuck to its body is delivered almost to the right address. Accuracy is what the plant is buying when it spends on petals, scent and nectar.