Theory 090/Food & Agriculture /Pollination ecology
Pollination Is Flower Density
Pollination is counted in bees per hectare. The bee may be counting flowers per visit.
Pollination success is set by flower density rather than by pollinator abundance, so a field with many pollinators and sparse flowers can set less fruit than one with few pollinators and dense flowers.
01The evidence
Fruit set varies widely at similar pollinator densities, and the variation tracks floral display density.
02The tension
Pollination deficits are attributed to pollinator declines, which predict fruit set from visitor numbers and miss the density effect on foraging efficiency.
03The mechanism
A pollinator foraging in a sparse patch spends more time travelling and less time visiting, and it may leave for a richer patch. Density sets the reward per unit effort.
That makes flower density the determinant, and predicts fruit set should track it better than visitor counts.
04What this is not
Those models predict from visitor numbers. This predicts from floral density, which explains deficits in well-pollinated fields.
05Predictions
- P1Fruit set should track flower density.
- P2Dense sparse-pollinator fields should outperform sparse dense ones.
- P3Density should predict better than abundance.
06Refutation
Fruit set tracking abundance at controlled density would restore the visitor model.
07What it changes
It would change planting design for pollination.