Minchinton Todd E
Institute for Conservation Biology and School of Biological Sciences, University of Wollongong, Wollongong, NSW 2522, Australia.
Oecologia. 2006 May;148(1):70-80. doi: 10.1007/s00442-005-0351-6. Epub 2006 Feb 1.
Herbivores may enhance plant recruitment, but such positive interactions may be overlooked in favour of obvious negative effects of herbivory on propagules. My objective was to determine whether larval insects that feed and develop within fruit of the mangrove Avicennia marina act as mutualist herbivores by increasing the dispersal of propagules without affecting their viability and emerging successfully as adults following dispersal of the propagule by water. Surveys revealed that frugivory is common throughout the mangrove forest, and fruit had up to six exit holes where larvae had emerged as adults. Larval insects did not affect the flotation of propagules with pericarps, a thin structure that provides buoyancy for dispersal by water. In contrast, after simulating germination by removing the pericarp, the majority of propagules with three exit holes floated on average for 20 h longer than those without exit holes, which sank immediately. Based on this evidence that frugivory could increase the dispersal potential of propagules, I predicted that propagules consumed by larval insects should disperse farther than undamaged propagules, and this was tested by quantifying the potential viability of propagules stranded on beaches at increasing distances (up to 20 km) from mangrove forests. Flies and moths emerged as adults after being transported tens of kilometres within mangrove propagules, revealing a novel mode of dispersal. Proportionally fewer potentially viable propagules were supplied to beaches at increasing distances from mangrove forests, however, indicating that larval insects negatively affect recruitment and are thus not acting as mutualist herbivores. Nevertheless, when transported back to the mangrove forest, seedlings established from propagules damaged by larval insects and stranded on beaches. Therefore, although frugivory does not preclude mangrove recruitment, its negative effects in the pre-dispersal environment may be intensified with increasing dispersal distance, thus limiting the long-distance supply of propagules and recruitment of mangroves.
食草动物可能会促进植物繁殖体的传播，但是这种积极的相互作用可能会被忽视，因为人们更关注食草动物对繁殖体的明显负面影响。我的目标是确定在红树林白骨壤果实内取食和发育的幼虫是否通过增加繁殖体的传播而成为互利共生的食草动物，同时不影响其活力，并在繁殖体通过水传播后成功羽化为成虫。调查显示，在整个红树林中，果实被取食的现象很常见，果实上有多达六个幼虫羽化后留下的出口孔。幼虫不会影响带有果皮的繁殖体的漂浮，果皮是一种薄结构，为通过水传播提供浮力。相反，在去除果皮模拟萌发后，大多数有三个出口孔的繁殖体平均漂浮时间比没有出口孔的繁殖体长20小时，没有出口孔的繁殖体会立即下沉。基于食果现象可以增加繁殖体传播潜力的证据，我预测被幼虫取食的繁殖体应该比未受损的繁殖体传播得更远，通过量化搁浅在距离红树林不同距离（最远20公里）海滩上的繁殖体的潜在活力对这一预测进行了测试。苍蝇和蛾子在红树林繁殖体中被运输数十公里后羽化为成虫，揭示了一种新的传播方式。然而，随着距离红树林越来越远，被供应到海滩的潜在可行繁殖体比例越来越少，这表明幼虫对繁殖有负面影响，因此不是互利共生的食草动物。尽管如此，当被带回红树林时，由幼虫损坏并搁浅在海滩上的繁殖体培育出了幼苗。因此，虽然食果现象并不妨碍红树林的繁殖，但它在传播前环境中的负面影响可能会随着传播距离的增加而加剧，从而限制了繁殖体的远距离供应和红树林的繁殖。
