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Exploitative competition and displacement mediated by eusocial bees: experimental evidence in a wild pollinator community
Behavioral Ecology and Sociobiology ( IF 2.3 ) Pub Date : 2020-11-27 , DOI: 10.1007/s00265-020-02924-y
Veronica R. Wignall , Matthew Brolly , Cassandra Uthoff , Kala E. Norton , Hannah M. Chipperfield , Nicholas J. Balfour , Francis L. W. Ratnieks

Eusocial bees are likely to be ecologically important competitors for floral resources, although competitive effects can be difficult to quantify in wild pollinator communities. To investigate this, we excluded honeybees (HBE treatment), bumblebees (BBE) or both (HB&BBE) from wild-growing patches of bramble, Rubus fruticosus L. agg., flowers in two eight-day field trials at separate locations, with complementary mapping of per-site local floral resource availability. Exclusions increased per-flower volume of nectar and visitation rates of non-excluded bees, compared to control patches with no bee exclusions (CON). There was a large increase in average nectar standing crop volume both at Site 1 (+ 172%) and Site 2 (+ 137%) in HB&BBE patch flowers, and no significant change in HBE or BBE, compared to CON patches. Foraging bee responses to exclusion treatments were more pronounced at Site 2, which may be due to lower local floral resource availability, since this is likely to increase the degree of exploitative competition present. Notably, at Site 2, there was a 447% increase in larger-bodied solitary (non-Apis/Bombus) bees visiting HB&BBE patches, suggesting ecological release from competition. Hoverflies showed no response to bee removals. Numbers of other non-bee insect groups were very small and also showed no clear response to exclusions. Our findings reveal patterns of competitive exclusion between pollinator groups, mediated by resource depletion by eusocial bees. Possible long-term implications of displacement from preferred flowers, particularly where alternative forage is reduced, are discussed. Understanding patterns of exploitative competition and displacement is necessary for pollinator conservation, particularly for vulnerable or threatened species. In this research, experimental methods reveal underlying patterns of resource competition exerted by eusocial bees in a wild pollinator community. We show that honeybees and bumblebees competitively displace each other and particularly solitary (non-Apis/Bombus) bees from bramble, an important native nectar and pollen source. Effects were stronger where local floral resource availability was identified to be limited. Notably, following experimental exclusion of both honey- and bumblebees from flowers, visitation by solitary bees increased by up to 447%, strongly suggesting ecological release from competition. These results highlight the need for informed landscape management for pollinator wellbeing, including appropriate honeybee stocking densities and improved floral resource availability.

中文翻译:

由真社会蜜蜂介导的剥削性竞争和流离失所:野生传粉媒介社区的实验证据

真社会性蜜蜂很可能是花卉资源的生态上重要的竞争者,尽管在野生传粉媒介群落中竞争效应难以量化。为了对此进行调查,我们在不同地点的两次为期八天的田间试验中,从野生生长的荆棘斑块(Rubus fruticosus L. agg.)中排除了蜜蜂(HBE 处理)、大黄蜂(BBE)或两者(HB&BBE),并进行了补充每个站点本地花卉资源可用性的映射。与没有蜜蜂排除 (CON) 的对照斑块相比,排除增加了每朵花的花蜜量和非排除蜜蜂的访问率。与 CON 斑块相比,HB&BBE 斑块花的站点 1 (+ 172%) 和站点 2 (+ 137%) 的平均花蜜直立作物量均大幅增加,而 HBE 或 BBE 没有显着变化。在站点 2,觅食蜜蜂对排斥处理的反应更为明显,这可能是由于当地花卉资源可用性较低,因为这可能会增加存在的剥削性竞争程度。值得注意的是,在站点 2,访问 HB&BBE 斑块的体型较大的独居(非蜜蜂/野蜂)蜜蜂增加了 447%,表明竞争中的生态释放。飞蝇对蜜蜂的清除没有反应。其他非蜜蜂昆虫群体的数量非常少,并且对排除也没有表现出明确的反应。我们的研究结果揭示了传粉者群体之间的竞争排斥模式,这是由真社会蜜蜂的资源消耗所介导的。讨论了替代首选花卉的可能长期影响,特别是在替代草料减少的情况下。了解剥削性竞争和流离失所的模式对于传粉媒介保护是必要的,特别是对于脆弱或受威胁的物种。在这项研究中,实验方法揭示了真社会性蜜蜂在野生传粉媒介群落中所施加的资源竞争的潜在模式。我们表明蜜蜂和大黄蜂竞争性地取代彼此,特别是来自荆棘的孤独(非蜜蜂/熊蜂)蜜蜂,荆棘是一种重要的本地花蜜和花粉来源。在确定当地花卉资源可用性有限的情况下,效果更强。值得注意的是,在实验中将蜜蜂和大黄蜂从花朵中排除后,独居蜜蜂的访问量增加了 447%,强烈表明竞争中的生态释放。
更新日期:2020-11-27
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