孑遗植物四合木(Tetraena mongolica)的濒危肇因与机制

The endangered characteristics and mechanism of the endemic relict shrub Tetraena mongolica Maxim

对我国特有单属种孑遗植物四合木(Tetraena mongolica Maxim)的地理分布、生境条件、种群数量动态、空间分布格局、种间关系、种群的生命表、生殖力表、有性生殖、无性繁殖和遗传变异等种群生态学特征及其濒危肇因进行了系统分析。研究结果表明:四合木种群为高群集分布,种群曲线属Leak凸型。年龄结构不合理,其存活曲线接近于Deevey毢型,且将演化为小种群,群落内的生境异质性显著,种群处于不稳定阶段。四合木从开花期到结果期,生殖分配(RA)呈下降的趋势,生殖过程中胚胎发生败育、种子向幼苗难以转化使其有性生殖受阻,生活史趋于断裂,是最终导致其濒危的重要内因。分布区城市化、工业化以及过度放牧等原因造成其种群孤立和生境破碎化是物种导致濒危的外因,四合木生态适应性和生境适宜性下降造成遗传多样性逐步丧失。同时提出对我国特有植物四合木进行异地保护的可能性与必然性。

The conservation biological study on the typical endangered plant species of Tetraena mongolica Maxim was carried out to examine endangered ecological process and characteristics in China from 1995 through 2006. The paper reviewed thoroughly the biological characteristics of tendency to endangered status, the geographic distribution, the habitat condition, the population dynamics, and the features of sexual reproduction and asexual propagation of T. mongolica. The authors also explained the modeling of the Leslie matrix, time series analysis for predicting population dynamics, fractal theory for describing population distribution pattern, and patterns of endangered population growth. Based on the comprehensive analysis, underlying endangered mechanisms and characteristics of T. mongolica were projected. T. mongolica distributes in confined west Erdos and the area is shrinking. Age structure indicates a population decline and spatial distribution follows a conglomeration pattern. The adaptation and living abilities demonstrate more weakness than the widespread species such as poorer species competition. The seed yields less and shows impotent. The percentage germination is lower and mortality of seedling higher. On the other hand, asexual propagation only functions limitedly as a kind of compensation after failure of sexual reproduction. In the community context, the favorable influence from other living organisms becomes weaker, whereas, the unfavorable influence stronger in natural situations as the result of disturbed ecological balance and reduced biodiversity. The endangered population of T. mongolica revealed a declining status with predicting model analysis. That eventually dues to both the internal factors, such as embryogenesis abortion, and feeble abilities of living, external factors such as and disturbances as well. Moreover, tougher disturbances would turn to the vital reason for T. mongolica to go extinct. In summary, the above endangered characteristics have accorded with the approved standards of ex situ conservation of relict plants. Therefore, T. mongolica should be protected with sufficient support of research.