蟹类在互花米草入侵红树林过程中的生态作用和适应机制

Introduced plant populations lose interaction with enemies, competitors and mutualists from their native ranges, and gain interactions with new species, under new abiotic conditions. Differences in the assemblage of interacting species, as well as in abiotic conditions, may explain the demographic success of the introduced plant populations relative to conspecifics in their native range. Within invaded communities, the new interactions and conditions experienced by the invader may influence both its demographic success and its effects on native biodiversity. Spartina alterniflora (hereafter Spartina), which is invading the entire Chinese coast, occupying mudflats throughout this range and displacing mangroves in the upper intertidal of southern China, is bound to affect the biotic interactions, resulting in changes of community structure and ecological functions. Coastal wetlands in China have a great diversity of native burrowing crabs. As physical ecosystem engineers, crabs play important roles in the intertidal ecosystems. Crabs burrow into the sediment and introduce air and plant nutrients that are vital to the mangroves. Invasive Spartina is increasing the population of some crab species by providing novel habitat and food. Other crabs that depend on the mudflat habitat will be negatively affected by Spartina invasion. In previous research, we have found that the effect of herbivorous crabs on Spartina varies with invasion stage. Some crabs are able to slow the invasion of Spartina in the early stages (seeds and seedlings), but crabs are not able to suppress mature Spartina clones that are expanding vegetatively. The ecotone between mangroves and Spartina provides a useful study system for understanding the interaction between native burrowing crabs and exotic Spartina. In this project, we will monitor the distribution and community structure of crabs in different habitats along a salinity gradient in Zhangjiang Estuary, Fujian, China. We will conduct field manipulation experiments and laboratory feeding assays, in order to disentangle the roles of the biotic (vegetation, predator, food source, competition from other crab species) and abiotic (light, temperature, salinity, sediment) factors on the habitat selection of crabs. In order to understand the mechanism and ecological effects of crabs on Spartina, we will document the seedling establishment and clone expansion of Spartina with and without the herbivory, and will observe the burrowing activities of crabs in the different habitats. We will then synthesize the ecological function and adaptive mechanism of burrowing crabs in response to Spartina invasion in mangroves of China, and then explain how biotic interaction and abiotic conditions influence invader success. The results of this study will cast light onto coastal wetland biological invasion issues, as well as provide scientific support for restoration and protection of mangroves in China.

生物交互作用是入侵生态学的核心问题之一。蟹类是红树林湿地底栖动物中的优势类群，多数种类具有掘洞行为，对潮间带生态系统扰动最为深刻。互花米草入侵中国东南沿海红树林，已迅速改变潮间带植被分布格局，势必影响被入侵地物种间的相互作用，导致群落结构和生态系统功能发生变化。本项目选择福建漳江口"红树林--互花米草生态交错带"，通过野外调查、红外摄像记录，监测异质生境中蟹类种类和数量动态；采用野外控制实验、室内喂饲实验、稳定同位素技术和聚酯树脂浇塑法测定蟹洞形态等方法，辨析决定蟹类生境选择的生物和非生物因素；从个体、种群、群落到生态系统等层次深入探讨蟹类的摄食和掘穴行为，阐明蟹类和互花米草相互作用的特征、变化过程及其对环境变化的响应机制；并从天敌、竞争、互利等多因子角度探讨物种间相互作用对互花米草入侵红树林的影响及其后果。研究结果可为应对滨海湿地生物入侵提供理论基础，为我国红树林保护和恢复提供科学依据。

生物交互作用是入侵生态学的核心问题之一。互花米草入侵中国东南沿海红树林，已迅速改变潮间带植被分布格局，影响被入侵地物种间的相互作用，导致群落结构和生态系统功能发生变化。.本项目选择福建漳江口“红树林——互花米草生态交错带”，监测红树林、互花米草和光滩3种生境中优势蟹类的时空动态。结果表明：褶痕拟相手蟹主要分布在红树林和互花米草生境；而长足长方蟹则主要分布在光滩生境。野外控制实验表明植被是影响蟹类分布的关键因子，红树林和互花米草的遮荫降低了生境中光照和温度，从而影响到蟹类的分布。.在研究过程中，我们发现啮齿动物取食互花米草的现象，通过在红树林、林缘及光滩3种生境开展围网控制实验。结果表明：啮齿动物取食增强了红树林抵御互花米草入侵的能力，动物取食和植物竞争共同导致红树林生境中互花米草更新失败。.为了更好地理解互花米草入侵对红树植物生长分布的影响，我们采用野外水位梯度控制平台对比研究红树植物秋茄、无瓣海桑和互花米草对淹水时间的响应，结合刈割和保留互花米草处理，研究互花米草对红树植物的相互作用强度与潮位梯度的相关关系。结果表明：互花米草会对红树植物的存活、生长产生抑制效应，并且其种间相互作用的性质和强度会随着潮位梯度、物种的不同而发生变化，从而影响到“红树林—互花米草生态交错带”中植被的分布格局和演替动态。.基于野外大尺度纬度梯度观测，我们推测种源和环境因子及其交互作用均可能影响互花米草在入侵地中国的有性繁殖沿纬度的渐变格局。通过在高、中和低纬度开展多个同质园实验，我们验证了这一猜想：大部分表型性状的地理变异格局在同质园中消失了，但种子结实率这一有性繁殖性状在同质园中保持和野外观测相同的沿纬度渐变格局，同时在中、高纬度同质园中总体的结实率高于低纬度的同质园。这也确凿证明了互花米草入侵中国并沿大尺度纬度扩散分布定居后，其有性繁殖性状出现遗传分化。环境和遗传的共同作用决定了该性状随纬度的变化规律。