The relationship between a flowering plant species and its pollinators may be regarded as one of energetics. The plant offers an energy reward in the form of nectar-and in some cases pollen-to attract foraging animals. Both food quality and quantity are crucial: the reward must be sufficiently nutritious and plentiful to induce visitation by flower-constant species, yet sufficiently limited to minimize the plant's energy expenditure and, more importantly, to force foragers to visit other flowers of the same species, and so to effect cross-pollina tion.
