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

了解植物如何调节它们对食草动物的脆弱性，是了解生物多样性和生态系统功能模式的核心。许多植物都有身体防御，如刺、刺或刺，以保护它们免受大型哺乳动物草食动物(如大象、长颈鹿、鹿和麋鹿)的伤害；然而，生产和维护这些防御系统的能量成本很高。因此，长出更多刺和刺的植物不太容易受到草食性疾病的影响，但用于投资于生长和繁殖的资源也更少，而生长和繁殖是植物健康的两个关键组成部分。对于干旱或贫瘠的非洲大草原上的植物来说，这种权衡尤其严重，因为那里的资源(如水和养分)稀缺，大型食草动物被吃掉的风险很高。因此，理论预测将出现在最大限度地提高防御效果的同时降低成本的战略。两种这样的策略是诱导防御(对食草动物的破坏快速产生)和联合防御(减少因靠近戒备森严的邻居而产生的食草性疾病的发生率)。该项目的目标是评估这些反食草动物策略的相对有效性及其相互作用，并确定不同物种的植物之间的积极联合作用如何改变资源投资的模式。面临相同进化压力的植物经常聚集在具有防御特征的相似套件上，即所谓的防御综合征。在非洲热带大草原，同一物种的个体可能会表现出强烈对比的防御综合征，这取决于他们与戒备森严的邻居的距离。例如，生长在多刺树冠下的植物，与生长在开放栖息地的同种植物相比，产生的刺更少，对模拟草食的诱导反应减弱。研究人员假设，这种差异是由支配植物防御性投资的环境线索的差异保持的，并将使用肯尼亚姆帕拉研究中心大型食草动物围栏内外对重点植物物种进行的移植实验来验证这一假说。研究人员还将对多个物种进行调查，以评估防御综合征在植物类群中的种内变异有多常见。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，本研究将阐明不同的反草食动物策略对植物适合性的独立和交互影响，并有助于为非洲大草原牧场的管理和本土植被的保护提供信息。

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.