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

了解植物调节其对食草动物的脆弱性的方式对于了解生物多样性和生态系统功能的模式至关重要。许多植物具有物理防御，如刺，刺或刺，以保护它们免受大型哺乳动物食草动物（例如，大象、长颈鹿、鹿和麋鹿）;然而，生产和维护这些防御系统在能量上是昂贵的。因此，产生更多刺和刺的植物不太容易受到草食动物的攻击，但也有更少的资源投资于生长和繁殖，这是植物健康的两个关键组成部分。这种权衡对于干旱或贫瘠的非洲稀树草原上的植物尤其严重，那里的资源（例如，水和养分）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最大化防御效果的策略的出现。两种这样的策略是诱导防御（对食草动物的损害迅速作出反应）和联合防御（在靠近防御良好的邻居的地方生长，减少食草动物的发生率）。该项目的目标是评估这些反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会聚集在类似的防御特征上，称为防御综合征。在非洲热带稀树草原上，同一物种的个体可以表现出强烈对比的防御综合征，这取决于它们与防御良好的邻居的接近程度。植物生长在多刺的树冠下，例如，产生较少的刺，并表现出减少诱导反应，模拟草食动物相对于同种在开放的栖息地。研究人员假设，这种差异是由管理植物防御性投资的环境线索的差异所维持的，并将使用在肯尼亚Mpala研究中心大型食草动物围栏内外进行的焦点植物物种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。通过调查的生物和/或非生物的力量，保持离散种内防御综合征，本研究将阐明独立和相互作用的影响，不同的抗草食动物的策略对植物的健身和帮助通知牧场的管理和非洲稀树草原的原生植被的保护。

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.