Ontogenetic changes in insect herbivory in birch (Betula pubesecens): the importance of plant apparency

1. Several theories aim at predicting changes in the interactions between plants and herbivores over the lifetime of a plant. Hypotheses based on ontogenetic changes in resource allocation to plant defence and in plant apparency lead to partly opposing predictions regarding the differences in levels of herbivory between juvenile and mature plant individuals. 2. We tested these predictions by measuring background foliar losses to insects in saplings and mature trees of downy birch (Betula pubescens) in ten sites along a latitudinal gradient from 60 to 69ºN in boreal forests of Northern Europe. 3. The percentage of consumed leaf area increased, and the variation in the levels of herbivory among plant individuals decreased, for tree sizes ranging from small saplings (2−12 cm tall) to large saplings (13−80 cm tall) and then to mature trees (3−18 m tall). 4. Small saplings had higher foliar quality for insects, as indicated by better performance of leafmining larvae of Eriocrania semipurpure...1. 现有多项理论旨在预测植物整个生命周期内，其与植食性动物（herbivore）之间的互作动态。基于植物防御的资源分配以及植物可见性（plant apparency）的个体发育（ontogenetic）变化所提出的各类假说，针对幼龄与成熟植株间的植食水平（herbivory）差异，得出了部分相悖的预测结果。 2. 本研究通过测量北欧寒带森林中沿北纬60°至69°纬度梯度分布的10个样地内垂枝桦（Betula pubescens）幼树（sapling）与成熟植株上的昆虫背景性叶片损失（foliar losses）量，对上述预测进行了验证。 3. 随着树体尺寸从小型幼树（株高2~12cm）过渡至大型幼树（株高13~80cm），再到成熟树木（株高3~18m），被取食的叶面积占比逐渐升高，而不同植株间的植食水平差异则逐步降低。 4. 小型幼树的叶片对于昆虫而言具备更高的品质，这一点可通过紫边潜蛾（Eriocrania semipurpurea）潜叶幼虫的生长表现更佳得到印证（原文内容未完整呈现）。