Data from: Seedling resistance, tolerance and escape from herbivores: insights from co-dominant canopy tree species in a resource-poor African rain forest

Although plants can reduce the impacts of herbivory in multiple ways, these defensive traits are often studied in isolation and an understanding of the resulting strategies is incomplete. In the study reported here, empirical evidence was simultaneously evaluated for the three main sets of traits available to plants: (1) resistance through constitutive leaf traits, (2) tolerance to defoliation, and (3) escape in space, for three caesalpiniaceous tree species Microberlinia bisulcata, Tetraberlinia bifoliolata and T. korupensis, which co-dominate groves within the lowland primary rain forest of Korup National Park (Cameroon). Mesh cages were placed around individual wild seedlings to exclude insect herbivores at 41 paired canopy-gap and understorey locations. After following growth and survival for c. 2 yr, caged and control treatments were removed, leaves harvested to determine nutrient and phenolic concentrations, leaf mass per area estimated, and seedling performance in gaps followed for a further c. 2 yr to quantify tolerance to the leaf harvesting. The more nutrient-rich leaves of the weakly shade-tolerant M. bisulcata were damaged much more in gaps than the two strongly shade-tolerant Tetraberlinia species, which had higher leaf mass per area and concentrations of total phenols. Conversely, the faster-growing M. bisulcata was better able to tolerate defoliation in terms of height growth (re-flushing capacity), but not at maintaining overall leaf numbers, than the other two species. Across gaps, insect-mediated Janzen-Connell effects were most pronounced for M. bisulcata, less so for T. korupensis, and not detectable for T. bifoliolata. The three species differed distinctly in their secondary metabolic profiles. Taken together, the results suggested a conceptual framework linking the three sets of traits, one in which the three co-dominant species adopt different strategies towards herbivore pressure depending on their different responses to light availability. This study is one of the first in a natural forest ecosystem to examine resistance to, tolerance of, and escape from herbivory among a group of co-occurring tropical tree species.

尽管植物可通过多种途径降低植食作用（herbivory）的负面影响，但现有研究常孤立地探讨各类防御性状，学界对植物演化出的综合防御策略仍缺乏完整认知。本研究同时针对植物三类核心防御性状展开实证评估：① 组成型叶片性状介导的抗生性；② 对叶片取食导致落叶的耐受性；③ 空间逃逸策略。研究对象为喀麦隆科鲁普国家公园低地原始雨林林丛中的三种云实科（Caesalpiniaceae）树种：双槽微柏林木（Microberlinia bisulcata）、四叶柏林木（Tetraberlinia bifoliolata）以及T. korupensis，三者共同构成该林丛的共优势种。研究人员在41对林窗-林下配对样地的野生幼苗周边架设网笼，以排除昆虫植食者的取食。在连续监测约2年的幼苗生长与存活情况后，移除网笼组与对照组样地的所有装置，采集叶片以测定其养分与酚类物质含量，同时估算单位叶面积干重（leaf mass per area）；随后继续监测林窗中幼苗的生长表现约2年，以量化其对叶片移除的耐受性。弱耐阴物种双槽微柏林木（M. bisulcata）的叶片养分含量更高，但其在林窗中的叶片受虫害损伤程度远高于另外两种强耐阴的四叶柏林木属（Tetraberlinia）物种，而后者具有更高的单位叶面积干重与总酚类物质含量。反之，生长速率更快的双槽微柏林木在株高生长（即新芽萌发能力）方面对落叶胁迫的耐受性更强，但在维持总叶数方面则不及另外两个物种。在所有林窗样地中，昆虫介导的詹曾-康奈尔效应（Janzen-Connell effect）在双槽微柏林木中最为显著，T. korupensis次之，而T. bifoliolata中未检测到该效应。三个物种的次生代谢产物谱存在显著差异。综合来看，本研究结果提出了一个连接三类防御性状的概念框架：三种共优势树种针对植食压力采取的防御策略各不相同，且这种策略差异与其对光照可获得性的响应特征直接相关。本研究是自然森林生态系统中，首次针对一组共分布热带树种同时探讨抗生性、耐受性与植食逃逸策略的研究之一。