Decision

Fig. 3.1. Diagram of the honeybee's decision-making process. The rate of 180┬░turns of the honeybee's round dance is used to quantify the subjective evaluation of objective information such as nectar concentration. The subjective values are used by the bees as the direct guide to choice behavior.

increased (this reflects von Frisch's "vigor"), and the rate of the dance decreased as flight costs increased. Rate of the dance was quantified as the number of 180┬░ changes in direction per minute. Thus, bees assessed and integrated both foraging costs and gains, then revealed their evaluation in the dance.

We since have used rate of the dance to quantify the functional relationship between costs and sucrose concentration and the bees' assessments, or subjective evaluations, of them. We discovered the following relationships. First, the relationship between sugar concentration and subjective concentration is non-linear (Waddington & Kirchner 1992); the dance rate increases with increasing concentration, but at a decreasing rate (Fig. 3.2). This is qualitatively consistent with the Weber-Fechner law of perception that generally describes the non-linear relationships between perception and the magnitude of stimuli (Carterette & Friedman 1974; see discussion in Perez & Waddington 1996).

Second, costs are subjectively weighted in relation to gains (Waddington 1985). That is, some incremental change in gains (e.g., joules obtained per flower visit) results in a lesser change in the dance rate than the same incremental change in cost (joules expended per flower visit for flight and handling).

More recently, we investigated whether bees make absolute or relative assessments of objective information (Raveret-Richter & Waddington

Fig. 3.2. Relationship between dance rate and sucrose concentration. (After Waddington & Kirchner 1992, Fig. 1A. Reprinted by permission of Blackwell Wissenschafts-Verlag, Berlin.)

Sucrose concentration (%)

Fig. 3.2. Relationship between dance rate and sucrose concentration. (After Waddington & Kirchner 1992, Fig. 1A. Reprinted by permission of Blackwell Wissenschafts-Verlag, Berlin.)

1993). Most foraging models assume the former (Shafir 1994). We allowed bees to forage at artificial flowers for solutions of various sugar concentrations. The concentrations were offered to the same bees sequentially in increasing order of concentration (i.e., 10%, 20%, ..., 60%; weight of solute per weight of solution) on the first day of foraging, and in decreasing order, starting at 60%, on the second day. We then analyzed the dance after each foraging trip. The question was whether the bees' assessment, as indicated by dance rate, was always the same whether visiting a particular concentration of sugar solution in increasing or decreasing order (indicating absolute assessment) or different (indicating a relative evaluation). The bees' assessments of a concentration clearly varied with context (Fig. 3.3). For example, the dance rate after feeding on the 40% solution placed in an increasing sequence was higher (15 reversals/min) than when placed in a decreasing sequence of concentrations (7 reversals/min). The results suggest that losses (decreasing sequence) are subjectively weighted in relation to increases because of the different magnitudes of change in dance rate with increases and decreases in concentration. Analogous phenomena are well known in human beings (Tversky & Kahneman 1981). In order to understand the meaning of these relationships to the attractiveness of flowers to pollinators in the field, it will be c j=

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