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The distributional patterns of six bumble bee (Bombus) species in discrete subalpine meadows in Utah were studied over the course of a summer. Data on the movements of individuals were obtained through mark—recapture studies of queens during nest initiation and of workers later in the summer. Censuses of the species and abundance of bumble bees and flowers in sample quadrats of 20 meadows revealed patterns of diversity, colony extinction (inferred from the absence of a species after it had been previously recorded in the meadow), and production of new reproductives. The results suggest that the number and diversity of queens that colonize a meadow in early summer is a function of meadow area. In mid to late season, after nest sites have been chosen and colonies established, meadow floristics (flower composition) governs within—meadow Bombus species composition and the persistence, ontogeny, and reproduction of bumble bee colonies. Workers appear not to utilize flowers outside the meadow where their colony is located. Specific results were that (1) mid— to late—summer bumble bee diversity was best correlated with meadow floristics, (2) flower compositions in meadows where local extinctions of Bombus occurred differed markedly from those where all species persisted, (3) the distribution of new reproductives among the meadows was independent of bombus species composition, and (4) late—season reproductive timing of Bombus flavifrons appeared to be a function of floristic composition and, particularly, nectar availability. These results underscore the importance of flower resources while downplaying the role of interactions among Bombus colonies and species in accounting for patterns of species persistence and colony reproduction.
Michael A. Bowers (Sat,) studied this question.