DISSERTATION RESEARCH: Plant defenses in African savannas: testing the effects of induced and associational defenses on plant phenotype, fitness and diversity

了解植物如何调节其对食草动物的脆弱性是理解生物多样性和生态系统功能模式的核心。许多植物都有物理防御，如刺、刺或刺，以保护它们免受大型食草哺乳动物（如大象、长颈鹿、鹿和麋鹿）的侵害；然而，生产和维持这些防御是非常昂贵的。因此，产生更多刺和刺的植物不太容易受到食草动物的侵害，但也有更少的资源用于生长和繁殖，这是植物适应性的两个关键组成部分。对于干旱或贫瘠的非洲稀树草原上的植物来说，这种权衡尤其严重，因为那里的资源（如水和营养物质）稀缺，被大型食草动物吃掉的风险很高。因此，理论预测了在降低成本的同时使防御效果最大化的战略的出现。两种这样的策略是诱导防御（对食草动物的损害迅速产生）和关联防御（由于在防御良好的邻居附近生长而减少草食的发生率）。该项目的目标是评估这些抗草食动物策略的相对有效性和相互作用，并确定不同物种植物之间的积极关联相互作用如何改变资源投资模式。面临相同进化压力的植物经常收敛于相似的防御特征，称为防御综合征。在非洲大草原上，同一物种的个体可以表现出强烈的防御综合症，这取决于它们与防御良好的邻居的距离。例如，与生长在开阔生境的同种植物相比，生长在多刺树冠下的植物产生的刺更少，对模拟草食的诱导反应也更弱。研究人员假设，这种差异是由控制植物防御性投资的环境线索的差异维持的，他们将在肯尼亚Mpala研究中心对大型食草动物保护区内外的焦点植物物种进行移植实验来验证这一假设。研究人员还将对多个物种进行调查，以评估防御综合征的种内变异在植物分类群中的普遍程度。通过研究维持离散种内防御综合征的生物和/或非生物力量，本研究将阐明不同抗食草动物策略对植物适应性的独立和相互作用，并有助于为非洲热带稀树草原的牧场管理和原生植被保护提供信息。

Understanding the ways in which plants modulate their vulnerability to herbivores is central to understanding patterns of biodiversity and ecosystem functioning. Many plants have physical defenses such as spines, thorns, or prickles that protect them against large mammalian herbivores (e.g., elephants, giraffes, deer, and elk); however, producing and maintaining these defenses is energetically costly. As a result, plants that produce more spines and thorns are less vulnerable to herbivory, but also have fewer resources to invest in growth and reproduction, two critical components of plant fitness. This tradeoff is particularly acute for plants in dry or infertile African savannas, where resources (e.g., water and nutrients) are scarce and the risk of being eaten by large herbivores is high. As a result, theory predicts the emergence of strategies that maximize the effectiveness of defenses while reducing their cost. Two such strategies are induced defenses (produced rapidly in response to damage by herbivores) and associational defenses (reduced incidence of herbivory derived from growing in close proximity to a well-defended neighbor). The goal of this project is to evaluate the relative effectiveness of, and interactions between, these anti-herbivore strategies and to determine how positive associational interactions among plants of different species alter patterns of resource investment. Plants facing the same evolutionary pressures frequently converge on similar suites of defensive characteristics, known as defense syndromes. In African savannas, individuals of the same species can exhibit strongly contrasting defense syndromes depending on their proximity to well-defended neighbors. Plants growing beneath thorny tree canopies, for example, produce fewer spines and exhibit a diminished induced response to simulated herbivory relative to conspecifics growing in open habitat. The researchers hypothesize that this difference is maintained by a disparity in the environmental cues that govern defensive investment in plants and will test this hypothesis using transplant experiments of focal plant species conducted inside and outside of large-herbivore exclosures in the Mpala Research Centre, Kenya. The researchers will also perform surveys of multiple species to evaluate how common intraspecific variation in defense syndrome is across plant taxa. By investigating the biotic and/or abiotic forces that maintain discrete intraspecific defense syndromes, this research will elucidate the independent and interactive effects of different anti-herbivore strategies on plant fitness and help inform the management of rangelands and the conservation of native vegetation in African savannas.