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 length) ; 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 template, the competition box. 2. Thresholds of depth, cost and temperature can be identified for each species of bee, delimiting domains within the box compatible with foraging by each bee species. 3. Changes through a day in temperature and in the depth and sugar content of nectar define the nectar trajectory through the box for a flower species in relation to microclimate and bee activity. 4. This approach allows systematic appraisal of the roles of accessibility, energy content and temperature in interspecific competition among bees for nectar, and draws attention to situations in which additional factors may be important. 5. By superimposing a bee-species-specific template on a representative nectar trajectory for a given flower species in a given situation, it is possible to make reasoned guesses about the expected interactions of foraging bee species with a novel flower species and with each other in a novel situation. Such guesses are required for evaluating the expected impact of honey-bees and other introduced pollinators on the pollination system of crops and natural vegetation. 6. Use of the competition box is illustrated in relation to dawn-to-dusk studies involving measurements of nectar concentration and volume, microclimate, flower form, and the tongue lengths and foraging activity of bees of different species.