Foraging Ecology of Bees in an Old Field

In an abandoned field near Ithaca, New York, bee species partitioned the available flower resources, primarily by foraging at different times of the season and by visiting different flower species. Honey bees (Apis mellifera) concentrated on different flower species than did native bees. In spring, most flowers bloomed along roadsides, in cultivated fields, or in forests. Many were clustered in spatial distribution and had short blooming times. Spring—flying native bees included many species adapted to forage on native flower species that bloom before the tree canopy closes. Apis mellifera, an introduced species, appeared to outcompete native bees at large clusters of attractive flower species such as apple and the crucifer Barbarea vulgaris. Blooming of introduced herbs increased in the field in early summer. This period of resource abundance was exploited primarily by primitively eusocial halictine bees. The multivoltine seasonal cycle of these bees allowed them to build populations over the season and to forage in large numbers in early and mid summer. Halictus ligatus was the most common early summer halictine. This species concentrated its foraging on different flowers than did other early summer bees, probably because of differences in innate flower preferences. A profuse bloom of native goldenrods in late summer was the seasonal peak of resource abundance. Honey bees partitioned goldenrod species with late summer native bees on the basis of flowering time. Native bees must complete their seasonal cycles and enter diapause before the killing frost. They therefore foraged on early—blooming goldenrod species such as Solidago juncea. In contrast, honey bees overwinter as active bees within their hives. They were most common on later—blooming goldenrods, where they collected much of the nectar required for overwintering. Competition among foraging bees was probably most important in the spring at this site. Partitioning of flower species and differences in seasonal flight times resulted primarily from differences in innate flower preferences, number of generations per season, and means of overwintering.