|Roulston, T'ai - AUBURN UNIVERSITY|
Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: April 1, 2000
Publication Date: N/A
Interpretive Summary: Some pollinators, notably all bees, depend upon pollen for all of their dietary needs for protein, fats and minerals, yet pollen so resists degradation that it is commonly used by paleontologists for reconstructing plant communities million of years old. This chapter surveys the nutritional qualities of pollen and reviews how animals digest pollen, with a focus on those species that accomplish the feat efficiently. Many animals digest pollen efficiently, bees especially so, and since the protein content of pollen ranges 10-fold, up to 60% dry weight, it seems reasonable to conclude that the nutritional value of the pollen that bees choose to collect strongly influences their reproductive success. The nutritional value of pollen will be an important consideration in the selection of flowering species for "bee pasture" when producing bees of agricultural value.
Technical Abstract: This chapter reviews the literature concerning digestion and nutrient content of pollen. Four topics are addressed in detail: 1) The mechanism of pollen digestion by animals; 2) The efficiency of mechanical and digestive removal of pollen content by various animals; 3) Range and taxonomic distribution of pollen nutrients, and 4) Adaptive hypotheses proposed to associate pollen chemistry with pollinator reward. Studies on the mechanism(s) of pollen digestion remain inconclusive, but suggest that differences in digestibility among pollen types may reflect differences in pollen wall porosity, thickness, and composition. Although hummingbirds reportedly digest pollen very poorly, most animals studied, including those that do not regularly consume pollen, can digest 50-100% of ingested grains. Overlooked and recent research of pollen protein content shows that pollen grains may contain over 60% protein, double the amount cited in some studies of pollen-feeding animals. Adaptive hypotheses that associate pollen starch and pollen caloric content with pollinator reward remain unsubstantiated when critically viewed through the lens of phylogeny.