Fowler Simon V
Department of Biology, University of York, Heslington, YO1 5DD, York, UK.
Oecologia. 1984 Jun;62(3):387-392. doi: 10.1007/BF00384272.
Two factors determining plant anti-herbivore defence investment fitness loss due to herbivory and the probability of herbivory occurring in the field were quantified for birch seedlings and trees. Fitness loss due to defoliation (assumed to be related to loss of growth increment compared to controls) appeared to be greater in seedlings compared to trees, but the result was equivocal. In contrast, seedling foliage at the field site - a typical habitat for birch - suffered much less natural defoliation than tree foliage, suggesting that seedlings are markedly less apparent to most birch herbivores than trees. This low apparency should result in lower investment in anti-herbivore defences by seedlings compared to trees - and being a strong effect, should outweigh the possibly greater growth loss suffered by seedlings, which in isolation would tend to increase their optimum defence investment compared to trees. This prediction was tested using palatability trials with a wide range of common birch herbivores and by direct quantification of anti-herbivore defences. Problems and assumptions inherent in these approaches are discussed, but it seems that birch seedlings are genuinely unapparent to herbivores, and consequently do not need the degree of defence investment required by trees.
针对桦树幼苗和成年树，对决定植物抗食草动物防御投入的两个因素进行了量化，这两个因素分别是因食草作用导致的适合度损失，以及在野外发生食草作用的概率。与成年树相比，因落叶造成的适合度损失（假定与对照相比生长增量的损失有关）在幼苗中似乎更大，但结果并不明确。相比之下，在野外环境（桦树的典型栖息地）中，幼苗叶片遭受的自然落叶比成年树叶片少得多，这表明与成年树相比，大多数桦树食草动物明显不太容易发现幼苗。这种低显眼度应导致幼苗相比成年树在抗食草动物防御方面的投入更低——而且由于这是一个显著的影响，应超过幼苗可能遭受的更大生长损失，单独来看，这种生长损失往往会使幼苗相比成年树增加其最佳防御投入。通过对多种常见桦树食草动物进行适口性试验以及直接量化抗食草动物防御来检验这一预测。讨论了这些方法中固有的问题和假设，但似乎桦树幼苗对食草动物确实不显眼，因此不需要成年树所需的防御投入程度。
