The Effect of Ant Nests on Plant Nutrition and Selection for Extrafloral Nectaries

花外蜜腺（EFNs）是位于植物叶和茎上的器官；它们分泌糖和氨基酸。目前，对于efn的进化和维持，唯一被广泛接受的假设是它们将掠食性节肢动物（尤其是蚂蚁）引诱到植物组织上，从而减少了食草动物对植物组织造成的伤害。然而，支持efn这一解释的证据是混杂的。这项研究的目的是测试另一种假说，即营养假说，以解释这一特征的进化和维持。在北美灌木金合欢（Acacia constricta）中，efn似乎鼓励蚂蚁在植物的生根区筑巢，在那里蚂蚁可以提高土壤矿质养分浓度，并可能增加植物的适应性。一些金合欢树的基部有蚁巢，而另一些则没有。金合欢树下的巢是动态的，每年夏天都会重新形成。先前在研究地点的工作表明，蚁巢土壤富含营养物质，这些营养物质经常限制植物的繁殖。拟议的研究采用实地和实验室实验来测试营养和保护对缢蛏适应性相关因素的相对重要性。这项研究还测试了蚂蚁巢穴提供的植物营养是否会通过生产高质量的食物奖励来反馈给蚂蚁。这项研究的结果将为植物-食草动物相互作用的进化生态学模型系统提供重要的见解。该项目还将更广泛地研究蚂蚁在干旱和半干旱生态系统中营养分配和积累方面所起的作用。该项目将在实验室、温室（阿拉斯加费尔班克斯大学）和实地（亚利桑那州西南研究站）为一名博士生和几名本科生提供培训。将特别努力招收从未有机会到阿拉斯加州以外地区旅行的本地和农村本科生。该项目将通过向生态学学生介绍一个具有高度生物多样性的新生物群落，从而拓宽他们的视野，该生物群落的结构与他们的家乡不同。

Extrafloral nectaries (EFNs) are organs located on leaves and stems of plants; they secrete sugars and amino acids. Currently, the only well-accepted hypothesis for the evolution and maintenance of EFNs is that they lure predatory arthropods, especially ants, onto plant tissues and thereby reduce the damage caused by herbivores. Evidence supporting this explanation for EFNs is mixed, however. The goal of this study is to test an alternative hypothesis, the nutrition hypothesis, for the evolution and maintenance of the trait. In the North American shrub, Acacia constricta, EFNs appear to encourage ants to nest within the rooting zone of the plant, where ants can enhance soil mineral nutrient concentrations and may increase plant fitness. Some acacia individuals have ant nests at the base and others do not. Nests under acacia are dynamic, forming anew each summer. Previous work at the study site has demonstrated that ant nest soils are enriched in nutrients that frequently limit plant reproduction. The proposed research uses field and laboratory experiments to test the relative importance of nutrition and protection to correlates of fitness for A. constricta. The research also tests whether enhanced plant nutrition, provided by ant nests, feeds back to the ants through the production of high-quality food rewards. Results from this research will contribute important insights to a model system used in the evolutionary ecology of plant-herbivore interactions. The project also will contribute more generally to the role that ants play in nutrient distribution and accumulation in arid and semi-arid ecosystems. The project will provide training for a Ph.D. student and several undergraduates in the laboratory and greenhouse (University of Alaska Fairbanks) and in the field (Southwestern Research Station, Arizona). Special effort will be made to recruit native and rural undergraduates who have never had the opportunity to travel outside the state of Alaska. The project will broaden the view of ecology students by introducing them to a new biome with high biodiversity, structured by climatic challenges unlike those of their home state.