THE COMPETITION BOX - A GRAPHICAL AID TO FORECASTING POLLINATOR PERFORMANCE

1. Three major determinants of bees' nectar-foraging patterns are the maximum depth at which nectar is accessible (dependent on bee tongue l ength); the minimum profitable energy content per flower (dependent on foraging costs and hence on bee body mass); and the minimum threshold temperature for flight. These form the axes of a three-dimensional te mplate, the competition box. 2. Thresholds of depth, cost and temperat ure can be identified for each species of bee, delimiting domains with in the box compatible with foraging by each bee species. 3. Changes th rough a day in temperature and in the depth and sugar content of necta r define the nectar trajectory through the box for a flower species in relation to microclimate and bee activity. 4. This approach allows sy stematic appraisal of the roles of accessibility, energy content and t emperature in interspecific competition among bees for nectar, and dra ws attention to situations in which additional factors may be importan t. 5. By superimposing a bee-species-specific template on a representa tive nectar trajectory for a given flower species in a given situation , it is possible to make reasoned guesses about the expected interacti ons of foraging bee species with a novel flower species and with each other in a novel situation. Such guesses are required for evaluating t he expected impact of honey-bees and other introduced pollinators on t he pollination system of crops and natural vegetation. 6. Use of the c ompetition box is illustrated in relation to dawn-to-dusk studies invo lving measurements of nectar concentration and volume, microclimate, f lower form, and the tongue lengths and foraging activity of bees of di fferent species.