Honeybees (Apis mellifera) and bumblebees (Bombus spp.) often undergo exploitative competition for shared floral resources, which can alter their foraging behaviour and flower choice, even causing competitive exclusion. This may be strongest in summer, when foraging conditions are most challenging for bees, compared to other times of the year. However, the seasonal dynamics of competition between these major pollinator groups are not well understood. Here, we investigate whether the strength of exploitative competition for nectar between honeybees and bumblebees varies seasonally, and whether competitive pressure is greatest in summer months. We carried out experimental bee exclusion trials from May to late September, using experimental patches of lavender, variety Grosso, in full bloom. In each trial, we compared the numbers of honeybees (HB) foraging on patches from which bumblebees had been manually excluded (bumblebee excluded, BBE) versus control (CON) patches, HB(BBE-CON). This measure of exploitative competition varied significantly with season. As expected, mean HB(BBE-CON) was significantly greater in summer trials than in spring or autumn trials. This was despite high nectar standing crop volumes in BBE patch flowers in spring and autumn trials. Mean HB(BBE-CON) was not different between spring and autumn trials. Our results show that nectar competition between honeybees and bumblebees varies seasonally and is stronger in summer than spring or autumn, adding to current understanding of the seasonality of resource demand and competition between bee species. This information may also help to inform conservation programs aiming to increase floral resources for bees by showing when these resources are most needed.

中文翻译：

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蜜蜂和大黄蜂之间剥削竞争的季节性变化。

蜜蜂和大黄蜂经常遭受共享花卉资源的剥削竞争，这可能会改变其觅食行为和花朵选择，甚至引起竞争性排斥。与一年中其他时间相比，夏季的觅食条件对蜜蜂最具挑战性，因此夏季可能最强。但是，人们对这些主要授粉媒介之间竞争的季节性动态知之甚少。在这里，我们调查蜜蜂和大黄蜂之间对花蜜的开发竞争强度是否随季节变化，并且在夏季月份竞争压力是否最大。我们从5月至9月下旬进行了实验性蜜蜂排除试验，使用了盛开的薰衣草品种Grosso进行实验。在每次审判中 我们比较了手动排除大黄蜂（排除大黄蜂，BBE）与对照（CON），HB（BBE-CON）的斑块上觅食的蜜蜂（HB）数量。剥削性竞争的衡量标准随季节而变化很大。不出所料，夏季试验中的平均HB（BBE-CON）明显大于春季或秋季试验。尽管在春季和秋季的试验中，BBE补丁花中的花蜜常备作物量很高。春季和秋季试验之间的平均HB（BBE-CON）没有差异。我们的结果表明，蜜蜂和大黄蜂之间的花蜜竞争随季节而变化，夏季比春季或秋季强，这加深了人们对资源需求的季节性和蜂种之间竞争的了解。