Data from: Foraging strategy predicts foraging economy in a facultative secondary nectar robber

In mutualistic interactions, the decision whether to cooperate or cheat depends on the relative costs and benefits of each strategy. In pollination mutualisms, secondary nectar robbing is a facultative behavior employed by a diverse array of nectar-feeding organisms, and is thought to be a form of cheating. Primary robbers create holes in floral tissue through which they feed on nectar, whereas secondary robbers, which often lack chewing mouthparts, feed on nectar through existing holes. Because primary robbers make nectar more readily available to secondary robbers, primary robbers facilitate the behaviors of secondary robbers. However, the net effect of facilitation on secondary robber fitness has not been empirically tested: it is unknown whether the benefit secondary robbers receive is strong enough to overcome the cost of competing with primary robbers for a shared resource. We conducted foraging experiments using the bumble bee Bombus bifarius, which can alternatively forage ‘legitimately’ (from the floral opening) or secondary-rob. We measured the relative foraging efficiencies (handling time per flower, flowers visited per minute, proportion of foraging bout spent consuming nectar) of these alternative behaviors, and tested whether the frequency of primary robbing and nectar standing crop in primary-robbed flowers of Linaria vulgaris (Plantaginaceae) affected foraging efficiency. Surprisingly, there was no effect of primary robbing frequency on the foraging efficiency of secondary-robbing B. bifarius. Instead, foraging strategy was a major predictor of foraging efficiency, with legitimate foraging being significantly more efficient than secondary robbing. Legitimate foraging was the more common strategy used by B. bifarius in our study; however, it is rarely used by B. bifarius foraging on L. vulgaris in nature, despite indications that it is more efficient. Our results suggest the need for deeper investigations into why bees adopt secondary robbing as a foraging strategy, specifically, the environmental contexts that promote the behavior.在互利共生交互中，个体选择合作或是欺骗的策略，取决于不同策略对应的相对成本与收益。在传粉互利共生体系中，次级盗蜜（secondary nectar robbing）是一类由多种取食花蜜的生物所采用的兼性行为，通常被视为一种欺骗策略。初级盗蜜者会在花组织上钻孔以取食花蜜，而次级盗蜜者往往缺乏咀嚼式口器，只能通过已存在的孔洞取食花蜜。由于初级盗蜜者会让次级盗蜜者更易获取花蜜，因此初级盗蜜者会促进次级盗蜜行为的发生。然而，这种促进作用对次级盗蜜者适合度（fitness）的净效应尚未经过实证检验：目前尚不清楚次级盗蜜者所获得的收益，是否足以抵消其与初级盗蜜者共享资源时的竞争成本。我们以双条熊蜂（Bombus bifarius）为对象开展觅食实验，该物种可选择采用“合法觅食”（从花开口处取食）或是次级盗蜜的行为模式。我们测定了这两种行为模式下的相对觅食效率，包括单花处理时间、每分钟访花数、觅食过程中用于消耗花蜜的时间占比，并检验了柳穿鱼（Linaria vulgaris，车前科Plantaginaceae）的初级盗蜜频率与被盗蜜花朵的花蜜存量是否会影响觅食效率。令人意外的是，初级盗蜜频率并未对次级盗蜜的双条熊蜂的觅食效率产生显著影响。相反，觅食策略是觅食效率的主要预测因子，合法觅食的效率显著高于次级盗蜜。在本实验中，合法觅食是双条熊蜂更常采用的策略；但在自然环境下，双条熊蜂极少会以柳穿鱼为对象开展合法觅食，尽管已有证据表明该策略效率更高。本研究结果表明，有必要深入探究熊蜂为何会将次级盗蜜作为一种觅食策略，尤其是明确驱动该行为产生的环境背景。