Trapline foraging by bumble bees: VII. Adjustments for foraging success following competitor removal

Animals collecting food from renewable resource patches scattered in space often establish small foraging areas to which they return faithfully. Such area fidelity offers foraging advantages through selection of profitable patches, route minimization, and regular circuit visits to these patches ("trapline foraging"). Resource distribution under field conditions may often vary in time, however, especially when competitors suddenly vanish and a number of patches become available for their neighbors. Previous studies suggested that site-faithful foragers of bumble bees quickly respond to such unexpected events by readjusting their foraging areas, although it is not clear how much their foraging performance was improved, beyond the simple relaxation of competitive pressure, or how they manifest such flexibility while persistently using certain foraging areas or paths. Here, we conducted indoor flight-cage experiments with bumble bees and found that a bee, when encountering a loss of its competitor, improved its foraging performance to a greater extent than expected from a simple relaxation of competitive pressure by increasing the size of its foraging area. Moreover, bees with better-established traplines achieved greater foraging areas after the loss of competitors, suggesting that bees do not necessarily need to "sample" neighboring patches to monitor temporal changes in environments. We discuss how periodical returns and route memory associated with accurate reward values could allow inherently conservative trapliners to make flexible adjustments, by effectively monitoring their circumstances and quickly readjusting to detected changes.