Flower constancy, insect psychology, and plant evolution

Individuals of some species of pollinating insects tend to restrict their v isits to only a few of the available plant species, in the process bypassin g valuable food sources. The question of why this flower constancy exists i s a rich and important one with implications for the organization of natura l communities of plants, floral evolution, and our understanding of the lea rning processes involved in finding food. Some scientists have assumed that newer constancy is adaptive per se. Others argued that constancy occurs be cause memory capacity for floral features in insects is limited, but attemp ts to identify the limitations often remained rather simplistic. We elucida te now different sensory and motor memories from natural foraging tasks are stored and retrieved, using concepts from modern learning science and visu al search, and conclude that newer constancy is likely to have multiple cau ses. Possible constraints favoring constancy are interference sensitivity o f short-term memory, and temporal limitations on retrieving information fro m long-term memory as rapidly as from short-term memory, but further empiri cal evidence is needed to substantiate these possibilities. In addition, re trieving memories mall be slower and more prone to errors when there are se veral options than when an insect copes with only a single task. In additio n to memory limitations, we also point out alternative explanations for new er constancy. We then consider the way in which floral parameters, such as interplant distances, nectar rewards, flower morphology, and floral color ( as seen through bees' eyes) affect constancy. Finally, we discuss the impli cations of pollinator constancy for plant evolution. To date there is no ev idence that flowers have diverged to favor constancy, although the appropri ate tests may not have yet been conducted. However, there is good evidence against the notion that pollinator constancy is involved in speciation or m aintenance of plant species integrity.