三种鼠尾草属植物开花特征及群落属性对熊蜂传粉和盗蜜行为转换的影响

It has been observed that bumble bees, one of the most important pollinators, displayed mixed foraging strategies between legitimate visiting and nectar robbing in many case studies. Based on analyses of recent literatures, I found two hypotheses were used to explain the switch between legitimate visiting and nectar robbing, namely, hypothesis of nectar intake efficiency and hypothesis of interspecific competition for limited nectar. The former one supposes that to obtain nectar more efficiently, bumble bees may switch their foraging behaviors from legitimate visiting to nectar robbing; while the latter one suggests that switch of the mixed foraging behaviors may help to avoid strong interspecific competition for limited nectar among different floral visitors. However, both hypotheses were not supported by experimental evidence. My earlier studies indicated the three Salvia species from Northwest Yunnan provided an ideal system to study the switch of mixed foraging behaviors between legitimate visiting and nectar robbing. All the three species were exclusively pollinated and robbed by bumble bees and moreover, some of the bumble bees were found to forage flowers in both ways. In addition, there were substantial variations of intensity of nectar robbing, floral traits and community characteristics among those species and populations from the same species. The present project will use three to five populations of each of the species to establish a comparative study system. I will test the hypothesis of nectar intake efficiency in study of population level. Some floral traits such as corolla tube length and width, nectar volume and sugar concentration will be calculated in each population of those species, and then, to link those parameters to the switch of mixed foraging behaviors between legitimate visiting and nectar robbing. The hypothesis of interspecific competition for limited nectar will be tested in study of community level. I will obtain some community characteristics such as floral identity and diversity, composition and abundance of floral visitors to detect whether these factors influence the switch of mixed foraging behaviors for bumble bees of the population from a given community. The results of this project will help us to understand the mechanism of occurrence of nectar robbing and moreover, enrich our knowledge of plant-pollination-nectar robbing system in this changing world.

野外观测发现，重要的传粉动物熊蜂在很多情况下兼具传粉和盗蜜的混合觅食策略；通过文献的系统分析显示有两种假说被用来解释该行为的发生，即觅食效率和资源竞争假说。前者是指熊蜂会调整觅食策略来获得更高收益，后者则认为是为了规避对群落中有限花蜜的竞争；但均缺乏必要的实验研究支撑。项目申请人前期工作显示，滇西北地区由熊蜂传粉和盗蜜的三种鼠尾草属植物提供了研究该问题的绝佳体系。它们之间及各自不同居群之间存在明显的盗蜜程度差异。本项目拟选取这三种植物的居群各3-5个，构建丰富的实验参考体系，通过居群水平的研究探测有关花部特征（如花冠开口和管长、花蜜量和浓度等）是否诱使熊蜂由正常传粉者转化为盗密者，验证觅食效率假说；通过群落水平实验研究有关群落因子（如花的多样性和访花者构成等）与访花行为转换的联系，验证资源竞争假说。相关研究结果将能帮助人们认识盗蜜发生机制，并丰富对于植物-传粉-盗蜜相互作用体系的全面认识。

盗蜜是自然界常见的一种欺骗性访花行为，前人研究发现盗蜜发生存在明显的时空变异，但是很少有研究揭示其发生规律及其驱动因素。本研究围绕预期目标开展了两部分内容，一方面关注居群季节内的盗蜜动态变化，选取了5个居群，连续两年根据花期进展进行多次调查，主要收集伴生植物及熊蜂种类及多样性，熊蜂觅食行为，盗蜜率，甘西鼠尾草开花特征，座果率、结实率等数据，结果显示盗蜜率随着花期发展有明显的下降趋势，盗蜜率与盗蜜熊蜂的丰度呈正相关，与群落中非盗蜜熊蜂丰度和伴生植物多样性呈负相关。另一方面关注居群间盗蜜变异规律，选取了20个居群，主要收集群落盗蜜率，熊蜂及开花植物丰度及多样性，以及不同尺度（500m、750m、1000m、1500m、2000m、2500m）的景观结构和景观配置等相关指标，结果显示不同景观因子对熊蜂多样性及丰度的影响随空间尺度变化，群落局部因素是影响熊蜂丰度的主要因素，其中伴生植物开花丰度以及丰富度与熊蜂丰度呈正相关，盗蜜率与群落中盗蜜熊蜂的丰度及群落的熊蜂多样性呈正相关；景观尺度下则是随着草地覆盖率的增大盗蜜率增加，而森林和人工地表覆盖率以及景观的异质性与盗蜜率呈负相关。另外，我们在研究中发现在试验区域的甘西鼠尾草有很普遍的蝗虫啃食叶片现象，我们在本项目的研究中期临时调整增加了此部分的研究内容。通过连续两年的蝗虫叶片啃食控制实验，结果显示，叶片啃食会改变甘西鼠尾草的花蜜的质量与数量从而影响传粉进而影响其繁殖成功，且人工模拟啃食与蝗虫啃食对甘西鼠尾草造成的影响不同。甘西鼠尾草对叶片啃食产生了耐性的防御策略，且耐性的程度因为传粉环境不同，在传粉丰度低的年份其耐受性防御策略更高。项目资助发表SCI论文1篇，待发表SCI论文4篇。培养硕士研究生2名，均在读。项目直接经费25万元，支出21.5844万元，各项支出基本与预算相符。剩余经费3.4156万元，将用于本项目的后续研究。