Why do pollinators visit proportionally fewer flowers in large patches?

Pollinators collect resources that are patchy., since flowers are usually a ggregated on several spatial scales. Empirical studies have established tha t pollinators almost invariably visit a smaller proportion of Bowers as pat ch size increases. This has not been adequately explained. Here I present d ata on the payoff curve achieved by bumblebees, Bombus lapidarius, when vis iting patches containing different numbers of inflorescences, and use the m arginal value theorem to predict the optimum duration of stay within patche s. The data demonstrate that visiting a declining proportion of inflorescen ces as patch size increases is an optimal strategy, if we assume that bees are attempting to maximise their rate of reward acquisition. I argue that t his occurs because starching for the remaining unvisited inflorescences is easier in a small patch. On large patches, bees visited more inflorescences per patch than predicted (although still visiting a declining proportion). I suggest that this may occur because bees are using simple departure rule s which result in near-optimal behaviour. I show that a departure rule base d on two successive encounters with empty inflorescences closely predicts o bserved behaviour.