POWRE: Structural Specializations of Protea Flowers and their Role in the Biology of African Sugarbirds: A Solution to Dilution?

有许多植物-传粉者关系的例子，其中一个或两个参与者表现出一定程度的专门化。例如，许多种类的植物都有长花冠的花，适合蜂鸟造访，但不包括蜜蜂等其他动物。在非洲最南部的开普弗洛王国，人们对授粉系统知之甚少。非洲海角是世界上植物学最丰富的地区之一，尽管它的许多物种主要依靠鸟类授粉，但它的鸟类多样性非常低。世界上只有9种鸟类，有400多种植物依靠它们授粉。其中最显眼的是开普敦糖鸟(Promerops Cafer)，它只在南非发现。它是一种中等大小(35克)、以花蜜为食的鸟类，与Proteaceae科植物，特别是Proteae属植物关系密切，其中至少有33种是鸟类授粉的。开普敦糖鸟的花序大而复杂，花蜜丰富，这是开普敦蜜鸟在冬季繁殖季节的主要食物来源。冬天是非洲开普省的雨季，因此糖鸟面临的一个问题是雨水稀释了ProTea的花蜜，但并不是所有的ProTea物种都同样脆弱。具有大碗或茶托状花序的蛋白质花蜜最容易被雨水稀释。然而，有些种类的蛋白质花具有浓密的毛茸茸的外层苞片，永远不会完全开放(所谓的“有胡子的蛋白质”)。在这些地区，即使是大雨，花蜜的浓度也几乎没有变化。文献中的一种描述和个人观察表明，开普敦糖鸟最喜欢繁殖的地区也往往有很大的林分，至少有一种胡须普特亚茶。从鸟类的角度来看，这将确保在其繁殖和低温对能量需求非常高的时候获得可靠的、高质量的食物来源，而且它的觅食受到短白天和需要留在鸟巢附近的限制。对于Proteas来说，在花朵结构上保护花蜜的投资应该会在雨后提高传粉者的保真度，这将促进授粉和高结实率。此外，PI正在研究保护Proteas花蜜的花卉专门化对开普省糖鸟生物学的重要性。利用Proteas和鸟类的全面位置数据库，PI正在确定糖鸟的繁殖区以及支持感兴趣的Protea物种的栖息地。PI正在调查这些栖息地，以确定繁殖鸟类的数量和存在的蛋白质种类，以及估计雨前和雨后可用花蜜的数量和质量。行为观察记录了取食行为的潜在变化，这可能与花蜜质量的变化有关。实验室研究正在确定蜜鸟在能量紧张的情况下能够维持身体质量的最低花蜜浓度，这将提供野外鸟类所能容忍的花蜜稀释程度的指示。这项研究的结果将提供有关蜜鸟和蛋白质的信息，它们可能对保护这些物种至关重要，因为南非西开普省是世界上生物多样性水平最高的地区之一。由于基础设施支持不足，削弱了她的研究计划，PI辞去了她在非洲的终身教职后，出现了在非洲工作的机会。这个项目是在1998年春国际为利用相对自由的失业而在访问南非期间产生的想法基础上发展起来的。这个项目对PI来说是一个难得的机会，因为它融合了她在禽类食蜜者生物学方面的专业知识，并有机会极大地拓宽她的生态专业知识。最重要的是，它为PI提供了一种保持高水平生产力的方法，同时她还可以重建自己的简历，寻找合适的永久教职。

There are many examples of plant-pollinator relationships in which one or both of the participants exhibit some degree of specialization. Many species of plants, for example, have flowers with long corollas that are suited to visitation by hummingbirds, but which exclude other animals such as bees. Little is known about pollination systems in the Cape Floral Kingdom of southern-most Africa. The African Cape is one of the richest areas in the world botanically, and although many of its species rely primarily on birds for pollination, its avian diversity is exceptionally low. There are only nine species of birds on which over 400 species of plants depend for pollination. Most conspicuous among these is the Cape sugarbird (Promerops cafer), which is found only in South Africa. It is a medium-sized (35 g), nectar-feeding bird that has a close relationship with plants in the family Proteaceae, and especially with species in the genus Protea, of which at least 33 are bird-pollinated. The Cape proteas produce large, compound inflorescences with copious nectar that is the major food resource of Cape sugarbirds during their winter breeding season. Winter is the rainy season in the African Cape, so a problem faced by sugarbirds is dilution of Protea nectar by rain, but not all species of Protea are equally vulnerable. Nectar of proteas with large bowl- or saucer-shaped inflorescences is most readily diluted by rain. Some species of proteas, however, produce flowers that have densely furred outer bracts that never open fully (the so-called "bearded" proteas). In these, the concentration of the nectar remains virtually unchanged by even heavy rain.Anecdotal accounts in the literature and personal observations suggest that areas most favored by Cape sugarbirds for breeding also tend to have significant stands of at least one species of bearded Protea. From the perspective of the bird, this would ensure a reliable, high quality food source at a time when its energy requirements are very high due to reproduction and low temperature, and its foraging is constrained by short days and the need to remain near the nest. For the proteas, the investment in floral structures to protect the nectar should pay off in enhanced pollinator fidelity after rains, which would facilitate pollination and high seed set.Together, the PIs are investigating the importance of the floral specializations that protect the nectar of proteas to the biology of Cape sugarbirds. Using comprehensive locality databases for both the proteas and the birds, the PI is identifying sugarbird breeding areas as well as habitats supporting the Protea species of interest. The PI is surveying these habitats to determine the number of breeding birds and the species of proteas present, as well as to estimate the quantity and quality of nectar available before and after rain. Behavioral observations document potential shifts in feeding behavior that might be associated with changes in nectar quality. Laboratory studies are determining the minimum nectar concentration on which sugarbirds are able to maintain body mass while energetically stressed, which will provide an indication of the degree of nectar dilution that can be tolerated by birds in the field.The results of this study will provide information about sugarbirds and proteas that might be crucial to the protection of these species in the face of increasing habitat degradation in South Africa's Western Cape, a region with one of the highest levels of biodiversity in the world.The opportunity to work in Africa arose after the PI resigned from her tenured faculty position because of inadequate infrastructural support that had crippled her research program. This project has grown out of ideas generated during a visit to South Africa that the PI took in spring 1998 to take advantage of the relative freedom of unemployment. The project is an exceptional opportunity for the PI because it blends her expertise in the biology of avian nectarivores with a chance to substantially broaden her ecological expertise. Most important, it offers the PI a way of maintaining a high level of productivity while she rebuilds her resume and searches for a suitable permanent faculty position.