Trapline foraging by bumble bees: III. Temporal patterns of visitation and foraging success at single plants

Abstract

We analyzed the temporal structure of visitation by bumble bee workers to a single Penstemon strictus plant growing in an array of conspecifics. When tested against a null distribution using a randomization model, the observed pattern of arrivals for the whole group of bees was random, but departures were clustered in time. Certain individuals visited the plant repeatedly and frequently throughout the day. These showed significantly regular arrival and departure schedules, which were likely produced by traplining. We explored whether these more frequent and regular foragers gained a higher reward than random or incidental plant visitors. Using an analytical model, Possingham predicted that a dominating forager that visited a simple, renewing resource in a regular pattern would garner higher and less variable rewards than random visitors. Inspired by these results, but interested in plant-level visitation, we constructed a simulation model of resource dynamics for a multiflowered plant with high visitation. The model incorporates the observed visitation schedules of all bees and independent reward dynamics for each flower on the plant. We calculated the rewards that observed bees would have collected given a range of resource-renewal parameters. More frequent visitors did not return to the plant when whole-plant resource levels were higher, but these visitors did get greater rewards. Their increased reward resulted from greater foraging efficiency, primarily through selecting (on average) more rewarding flowers than those selected by less frequent, random visitors.