Monitoring Flower Visitation Networks and Interactions between Pairs of Bumble Bees in a Large Outdoor Flight Cage

Pollinators, such as bees, often develop multi-location routes (traplines) to exploit subsets of flower patches within larger plant populations. How individuals establish such foraging areas in the presence of other foragers is poorly explored. Here we investigated the foraging patterns of pairs of bumble bees (Bombus terrestris) released sequentially into an 880m2 outdoor flight cage containing 10 feeding stations (artificial flowers). Using motion-sensitive video cameras mounted on flowers, we mapped the flower visitation networks of both foragers, quantified their interactions and compared their foraging success over an entire day. Overall, bees that were released first (residents) travelled 37% faster and collected 77% more nectar, thereby reaching a net energy intake rate 64% higher than bees released second (newcomers). However, this prior-experience advantage decreased as newcomers became familiar with the spatial configuration of the flower array. When both bees visited the same flower simultaneously, the most frequent outcome was for the resident to evict the newcomer. On the rare occasions when newcomers evicted residents, the two bees increased their frequency of return visits to that flower. These competitive interactions led to a significant (if only partial) spatial overlap between the foraging patterns of pairs of bees. While newcomers may initially use social cues (such as olfactory footprints) to exploit flowers used by residents, either because such cues indicate higher rewards and/or safety from predation, residents may attempt to preserve their monopoly over familiar resources through exploitation and interference. We discuss how these interactions may favour spatial partitioning, thereby maximising the foraging efficiency of individuals and colonies.传粉者（Pollinators）如蜜蜂，通常会演化出多位点觅食路线（巡游路线，traplines），以利用大种群植物中的部分花簇。目前学界对觅食者在存在同类其他个体的情况下，如何建立此类觅食区域的问题，尚缺乏充分探索。本研究针对成对先后被释放至880平方米室外飞行笼内的大地熊蜂（Bombus terrestris）的觅食模式展开了调查，该飞行笼内设有10个饲喂站（人工花）。通过安装在花上的运动敏感型摄像机，我们绘制了两只熊蜂的访花网络（flower visitation networks），量化了二者的互动行为，并对比了它们全天的觅食成功率。总体而言，先被释放的熊蜂（定居者）的飞行速度比后释放的熊蜂（新来者）快37%，采集的花蜜量多77%，因此其净能量摄入率比新来者高出64%。然而，随着新来者逐渐熟悉花阵列的空间布局，这种先验经验优势会逐渐减弱。当两只熊蜂同时访问同一朵花时，最常见的结果是定居者驱逐新来者。在极少数情况下，若新来者成功驱逐定居者，二者都会增加对该花的回访频率。这类竞争性互动虽仅实现了部分空间重叠，但仍使成对熊蜂的觅食模式间产生了显著的空间重叠。尽管新来者最初可能会借助社会线索（如足部留下的嗅觉印记，olfactory footprints）来利用定居者已访问过的花——这类线索或许预示着更高的花蜜报酬和/或更安全的捕食环境——但定居者会试图通过资源利用竞争与干扰竞争，保住自己对熟悉资源的独占权。我们讨论了这类互动如何促进空间分隔，从而最大化个体及蜂群的觅食效率。