鸟类取食活动对桑树种子传播和萌发的影响

Effect of Bird Predation on Dissemination and Germination of Mulberry Seeds

种子(果实)作为桑树(Morus L.)的有性繁殖体,其传播和萌发关系到桑属植物种群延续以及动态更新,而食果鸟类在桑树种子的传播和萌发过程中发挥的作用以及与桑树种群之间形成的生态互利关系值得探讨。在调查实生桑植株的生长、结实,种子传播、萌发和幼苗存活等特性的基础上,对鸟类取食桑椹、传播桑种子的行为进行观察。结果如下:桑树植株间的形态、果实大小和单果种子数量等特征存在较大差异,表明桑树个体间的种子繁殖和传播能力存在差异;自然环境中桑树的果实基本散落在树冠范围内(直径<5 m),随着散落距离的增加,地表果实数量和种子萌发数量减少,但种子萌发率增加(2.6%~7.9%),而种子成苗率和次年存活率均没有差异(分别为18.8%和2.7%);鸟类对桑种子的传播距离远远大于桑树自身散落的距离,含有桑种子的鸟类粪便64%着落在适宜种子萌发和种群定居的水源区;鸟类未消化并通过粪便排泄桑种子的萌发率与去除果肉(皮)的桑种子萌发率没有显著差异(萌发率均>75.0%),但显著高于未经处理桑种子的萌发率(46.7%)。上述结果提示,桑树果实为食果鸟类提供了食物,鸟类取食活动不仅扩大了桑树种子的传播距离,而且促进了种子的萌发,这也是食果鸟类与桑树种群互利共生的证据之一。

Seed （fruit） is the propagule of mulberry （Morus L.）. Its dissemination and germination influence maintenance and regeneration of Morus plant populations. It is necessary to study the role of frugivorous birds in mulberry seed dissemi- nation and germination and to uncover the ecological meaning of mutual benefits between frugivorous birds and mulberrypopulation. In this study, characteristics of mulberry plant growth, fruit bearing, seed dispersal, seed germination and seedling survival were investigated. Meanwhile, be- haviors of birds feeding mulberry fruit and spreading mul- berry seeds were observed. The results showed that： （ 1 ） Remarkable differences between individual mulberry plants existed in traits such as plant shape, fruit size and seed number per fruit, suggesting that seed reproduction and dissemination of individual mulberry plants differed witheach other. （2） Under natural condition, mulberry fruits were mainly disseminated within the range of plant canopy （d〈5 m）. With the increase of dissemination distance, the number of fruits and germinated seeds on the ground was decreased, but seed germination rate was increased （2.6%-7.9%）, while emergence rate （18.8%） and the-second-year survival rate （2.7%） of seedlings had no difference. （3） Distance of seeds spread by birds was much longer than that by mulberry trees. Sixty-four percent of bird-defecated mulberry seeds were distributed in water-source area which is suitable for seed germination and population establishment. （4） Germination rate of bird-defecated seeds did not differ with that of pulp/ peel-removed mulberry seeds （germination rates 〉 75.0%）, but was significantly higher than that of untreated intact seeds （46.7%）. Our results demonstrate that mulberry fruit provides food source for frugivorous birds, and feeding activity of birds not only increases dissemination distance but also promotes seed germination of mulberry seeds. This relationship provides one of the evidences for mutual benefits between frugivorous birds and mulberry population.