Exploring the `Harperian' paradox: Leaving descendants in a crowded plant world

近邻之间的竞争通常被认为是自然选择中最激烈的力量之一，它塑造了植物功能性状的进化和多样性。大多数传统的理论为植物的成功进化策略在资源限制（竞争能力）是基于一个“大小优势”的假设，其中优势通常涉及更大的成功，在吸收/消耗有争议的资源，因此通常与更大的增长积累和更大的最大潜在的身体大小（MAX）。然而，我最近的研究指出了一种涉及“生殖经济优势”假设的替代解释，即在严重拥挤的社区内，生殖成功通常更大，而不是具有较大最大值的物种，而是具有较高“生殖力分配”的物种，即单位时间每单位亲本植物大小产生更多后代（有性或克隆）。本研究将利用温室研究、自然植被的田间试验和加拿大安大略东部地区植物群的大规模普查，确定开花植物生殖力分配的主要组成部分，从而确定开花植物的生殖经济能力。重点将放在有风险的物种和与农业边际土地（如老田地）的生态系统服务有关的植被上。主要的预测是，高繁殖力分配是由四个潜在的大小度量促进的：（i）相对较小的MIN（产生种子或克隆后代的最低阈值亲本体型）;（ii）相对较高的地上体重密度（每单位物理空间占用的干质量）;（iii）相对小的种子大小-即，在所有其他条件相同的情况下，产生较小种子的植物每单位植物体大小可以产生更多的种子;以及（iv）相对较小的叶尺寸-即，对于给定的支持营养组织的身体尺寸，产生较小叶的植物可以产生更多的叶（较高的“叶化强度”），这使得更大的腋生“芽库”（每单位身体大小）可用于作为克隆和/或有性生殖分生组织的部署。有一个更大的芽库，我们可以预测，也意味着更多的分生组织可用于战略部署在建筑/生长形式的可塑性（例如，在可变的光制度下的分支强度）的表达，或作为一个“储备”的生存和补偿后，组织损失食草动物或干扰。 这些项目为期五年，将涉及培训2名博士生、4-5名硕士生和10名本科论文生-平均每年有3-4名研究生和2名学士（荣誉）论文生/暑期学生技术人员在我的实验室工作。

Competition between near neighbours is conventionally regarded as one of the most intense forces of natural selection that has shaped the evolution and diversity of functional traits in plants. Most of the traditional theory for evolved strategies of success in plants under resource limitation (competitive ability) is based on a `Size Advantage' hypothesis, where superiority involves generally greater success in uptake/depletion of contested resources, typically associated therefore with greater growth accumulation and larger maximum potential body size (MAX). My recent research however points to an alternative interpretation involving a `Reproductive Economy Advantage' hypothesis, where reproductive success within severely crowded neighbourhoods is generally greater, not for species with larger MAX, but for species with higher `fecundity allocation', i.e. production of a larger number of offspring (sexual or clonal) per unit parent plant size per unit time. The research proposed here will use greenhouse studies, field experiments in natural vegetation, and large scale census surveys of the regional flora in eastern Ontario, Canada to identify the major components of fecundity allocation and hence capacity for reproductive economy in flowering plants. Emphasis will be placed on species at risk and vegetation associated with ecosystem services of marginal lands for agriculture (e.g. old fields). The main predictions are that high fecundity allocation is promoted by four potential size metrics: (i) relatively small MIN (minimum threshold parental body size for producing seed or clonal offspring); (ii) relatively high above-ground body mass density (dry mass per unit of physical space occupancy); (iii) relatively small seed size - i.e. all else being equal, a plant that makes smaller seeds, can make more of them per unit plant body size; and (iv) relatively small leaf size - i.e. a plant that makes smaller leaves can make more leaves for a given body size of supporting vegetative tissue (a higher `leafing intensity'), which enables a larger axillary `bud bank' (per unit body size) available for deployment as clonal and/or sexual reproductive meristems. Having a larger bud bank, we can predict, also means that more meristems are available for strategic deployment in the expression of architectural/growth-form plasticity (e.g. for branching intensity under variable light regimes), or as a `reserve' for survival and compensation following tissue loss to herbivores or disturbance.  These projects, over five years, will involve training for 2 PhD students, 4-5 MSc students, and 10 undergraduate thesis students - with an average of 3-4 graduate students and 2 BSc (Hons) thesis students / summer student technicians working in my lab each year.