Effects of nectar variance on learning by bumble bees

Abstract. The variation in standing crops of nectar among flowers within a species is usually very high. This nectar variance may decrease a forager's ability to estimate the mean reward offered by alternative plant species. Consequently, learning performance under high nectar variance may be reduced. To examine this prediction, bumble bees were tested for their abilities to learn to discriminate rewarding from non-rewarding flowers under four levels of nectar variance. The learning rate of bumble bees was significantly lower with nectar variance than with no variance. However, learning rates did not differ among the three levels of nectar variance. The results suggest that under increasing nectar variance bees do not increase sampling period, but instead base their foraging decisions on the less reliable information from a certain maximum number of flowers sampled.