Zammit Charles, Westoby Mark
Ecology. 1987 Dec;68(6):1984-1992. doi: 10.2307/1939889.
Banksia ericifolia is killed by fire and so depends upon seeds for persistence. In contrast, B. oblongifolia can persist after fire by resprouting from protected buds, as well as by recruiting seedlings. These serotinous species coexist in the fire-prone scrublands of the Sydney Basin. Here we report experiments that compared seed release from cones retained in the canopy, seed germination, and seedling establishment in these two species. B. oblongifolia seeds were released more quickly than B. ericifolia seeds after a fire, and B. oblongifolia follicles opened and shed seeds after exposure to lower temperatures than those of B. ericifolia. B. oblongifolia seeds germinated more quickly than those of B. ericifolia. The relative growth rates and leaf mass ratios (mean ratio of leaf dry mass to plant dry mass over sequential harvests) of the two species did not differ. Root : shoot ratios were significantly large and biomass allocation to roots was faster in B. oblongifolia seedlings. B. ericifolia seedlings survived low and intermediate levels of droughting better than B. oblongifolia under greenhouse conditions. In a field experiment in which water was not limiting, large B. oblongifolia seedlings had the highest survival rate. These results suggest that selection has acted on B. ericifolia to minimize the chance of zero seedling survival by distributing the risks over more than one germination episode. There was no consistent evidence to support the hypothesis that selection on this species has increased its probability of seedling survival during any one germination opportunity relative to its congener.
橙黄银桦会被火烧死，因此依赖种子来延续种群。相比之下，长叶银桦在火灾后可通过受保护的芽进行萌蘖以及通过幼苗补充来延续种群。这些具迟裂果的物种共存于悉尼盆地易发生火灾的灌丛中。在此我们报告了一些实验，这些实验比较了这两个物种树冠中留存球果的种子释放、种子萌发及幼苗定植情况。火灾后，长叶银桦的种子比橙黄银桦的种子释放得更快，并且长叶银桦的蓇葖果在暴露于比橙黄银桦更低的温度后就会打开并散落种子。长叶银桦的种子比橙黄银桦的种子萌发得更快。这两个物种的相对生长速率和叶质量比（连续收获过程中叶干质量与植株干质量的平均比值）没有差异。长叶银桦幼苗的根冠比显著更大，且根系生物量分配更快。在温室条件下，橙黄银桦幼苗在低水平和中等水平干旱情况下的存活情况比长叶银桦更好。在一个水分不构成限制的田间实验中，大型长叶银桦幼苗的存活率最高。这些结果表明，自然选择作用于橙黄银桦，通过在多个萌发阶段分散风险，将幼苗零存活的几率降至最低。没有一致的证据支持这样的假说，即相对于同属植物，对该物种的自然选择增加了其在任何一次萌发机会中幼苗存活的概率。
