School of Biological Sciences, The University of Queensland, Brisbane, Qld 4072, Australia.
Am J Bot. 2013 Jun;100(6):1127-36. doi: 10.3732/ajb.1200115. Epub 2013 May 27.
Plants that invest in large, heavy seeds and colorful, fleshy fruits or analogous structures seem adapted for dispersal by large vertebrates. Some such plants, like Australian cycads in the genus Macrozamia, do not disperse well, which could be explained by seed-dispersal relationships with megafauna that are rare or extinct in contemporary ecosystems. Such plants provide an opportunity to investigate the ecological consequences of low seed-dispersal distances. •
We investigated seed dispersal of Macrozamia miquelii in Central Queensland by tracking the fate of marked seeds, identifying the dispersal fauna and quantifying population demography and spatial structure. •
We found that 70-100% of marked seeds remained within 1 m of maternal females (cycads are dioecious). Of the 812 seeds recovered (from 840 originally marked) only 24 dispersed >1 m from maternal females, the greatest observed dispersal being 5 m. We found an average of 2.2 seedlings and 0.7 juveniles within 1.5 m of mature females, which suggests that most seeds that remain in the vicinity of maternal females perish. Within-stand densities ranged between 1000 and 5000 plants/ha. The brushtail possum Trichosurus vulpecula was the only animal observed to move the seeds. •
Macrozamia are adapted for dispersal by megafauna that are rare or absent in contemporary ecosystems. We argue that Macrozamia are "grove forming" plants that derive ecological benefit from existing as high-density, spatially discrete populations, the function of megafaunal dispersal adaptations being the infrequent dispersal of seeds en masse to establish new such groves in the landscape.
投资于大型、重型种子和色彩鲜艳、肉质果实或类似结构的植物，似乎适合通过大型脊椎动物传播。一些这样的植物，如澳大利亚的麦克罗泽亚苏铁属植物，传播效果不佳，这可以用与现代生态系统中罕见或已灭绝的巨型动物的种子传播关系来解释。这些植物为研究低种子传播距离的生态后果提供了机会。
我们通过追踪标记种子的命运、识别传播动物、量化种群动态和空间结构，调查了昆士兰中部麦克罗泽亚苏铁的种子传播。
我们发现，标记种子中有 70-100%留在母株雌性个体（苏铁是雌雄异株）周围 1 米以内。在回收的 812 颗种子中（最初标记了 840 颗），只有 24 颗种子从母株雌性个体传播超过 1 米，观察到的最大传播距离为 5 米。我们发现，在成熟雌性个体周围 1.5 米范围内平均有 2.2 株幼苗和 0.7 株幼树，这表明大多数留在母株附近的种子都会死亡。林内密度在 1000 到 5000 株/公顷之间。唯一观察到移动种子的动物是帚尾袋貂。
麦克罗泽亚苏铁适应于大型动物传播，而这些大型动物在现代生态系统中罕见或不存在。我们认为，麦克罗泽亚苏铁是“林状”植物，从高密度、空间离散的种群中获得生态效益，大型动物传播适应的功能是将种子大规模偶然传播到景观中的新林状植物中。
