捕食者对榕-蜂共生系统稳定性的影响及其机制研究

Mutualistic interactions often involve tens or hundreds of species that form complex networks, which is regarded as the architecture of biodiversity. Partition of niche, spatial heterogeneity and host punishment hypothesizes, have been proposed, yet, neither of them can fully explain the stability of mutualistic systems. Recently, a few studies have suggested that trophic cascade induced by predators play crucial role in change species composition and abundance in mutualistic systems. Trophic cascade induced by predator might be a new mechanism that could maintain the stability of mutualistic systems. However, this hypothesis needs data support. Fig-fig wasp system is an ideal model to study the role of predator induced trophic cascade on maintaining cooperative relationship in a mutualistic system. In this system, ants can prey on fig wasps and indirectly influence reproduction of figs and all the fig wasp species develop in the syconia of figs forming a fig wasp community. In this grant proposal, we plan to use Ficus racemosa-pollinating wasp mutualistic system to explore effects of predation on fig wasp community structure and fitness of figs from a view of whole community. We will use analytic methods such as: analysis of similarity, non-metric multi-dimensional scaling, and similarity percentages, to compare the community structure of fig wasps and uncover the underlying reasons which cause the dissimilarity. We also aim at exploring procedure of trophic cascade by studying behavior of ants and fig wasps using a wide array of behavioral bioassays and methods in chemical ecology. Finally, we test trophic cascade in this system by means of an exclosure experiment. The results of this work will shed new light on theory of maintenance of cooperative systems and serve as a guide to implement biological control.

揭示互利共生系统稳定性维持机制是理解生物多样性的产生和生态系统稳定性的基础。传统的生态位分化、生存空间异质性及寄主的"惩罚"理论都不能很好的解释共生系统稳定性维持，而捕食者能以营养级联的方式改变低营养级物种的组成和丰度，可能是一种新的机制。蚂蚁-榕小蜂-榕树系统是从整体群落的角度研究营养级联效应对共生系统稳定性影响的理想模型。本研究以聚果榕-榕小蜂共生系统为对象，探讨捕食小蜂的黄猄蚁和游举腹蚁对该共生系统的营养级联效应及其机理。使用基于群落整体差异的分析方法检验捕食者对小蜂整体群落的影响并解析其原因，使用化学生态学手段证明营养级联作用的过程，最后通过野外控制实验进行验证。其结果将为共生系统稳定性维持的理论研究提供新思路，并对以天敌为手段的生防策略的使用具有指导意义。

互利共生的物种与生境中其他物种形成了互作的网络，构成了生物多样性的基础。揭示互利共生系统稳定性维持机制是理解生物多样性的产生和生态系统稳定性的前提之一。天敌能以营养级联的方式改变低营养级物种的组成和丰度，可能是一种新共生系统稳定性维持机制。蚂蚁-榕小蜂-榕树系统是从整体群落的角度研究营养级联效应对共生系统稳定性作用机理的理想模型。本研究以西双版纳地区常见的聚果榕-榕小蜂共生系统为对象，探讨捕食小蜂的蚂蚁对榕-蜂共生系统的营养级联效应及其机理。同时阐明该体系中，与蚂蚁共生的同翅目昆虫角蝉（Homoptera: Membracoidea）基于化学信号模拟的自我保护机制。.研究结果表明，黄猄蚁（Oecophylla smaragdina）是聚果榕上主要的蚂蚁种类。黄猄蚁能在非传粉小蜂产卵时捕食非传粉小蜂，而对传粉小蜂的捕食较少。与未隔离蚂蚁的对照相比，人为隔离了蚂蚁之后榕果上产卵的非传粉小蜂数量较多，非传粉小蜂的产卵孔数量较多，而进入榕果产卵的传粉小蜂数量减少。对野外的榕树小蜂群落进行调查结果表明，那些有黄猄蚁栖息的榕树上小蜂子代群落以传粉小蜂为主，榕果种子产量较大；而那些没有黄猄蚁栖息的榕树上，榕果产生的小蜂以非传粉小蜂为主，榕果的种子产量低。.在榕树的果枝上黄猄蚁与角蝉的数量呈现显著的正相关关系。化学分析的结果表明，在与聚果榕树枝、传粉榕小蜂、非传粉榕小蜂以及蚂蚁的表皮化学物质的比较中，角蝉的体表物质与榕树树枝的表皮物质最为接近。当通过实验除去角蝉的体表物质后，黄猄蚁对角蝉的取食增加了。但是，当我们将树枝的表皮物质包裹在除去体表物质的角蝉身体上后，蚂蚁的捕食降低了。蚂蚁对榕树树枝、角蝉、传粉小蜂以及非传粉小蜂的体表物质都表现出行为上的趋向性。.综上所述，蚂蚁作为榕树上重要的捕食者通过其对榕小蜂的捕食以及与角蝉的共生对榕树上的昆虫群落产生了重要的影响，这种影响能以营养级联的方式传递到宿主榕树。在由蚂蚁-角蝉以及榕树-榕小蜂共同组成的这一复杂系统中，食物网的调节和化学信号调节共同作用，构成了该系统中物种稳定共存的能量和信息基础。