Bird Predation, Forest Insects, and Growth of Cottonwoods: Bottom-up and Top-down Influences on a Trophic Cascade in a Threatened Habitat

鸟类捕食、森林昆虫和三叶杨的生长：自下而上和自上而下对受威胁栖息地营养级联的影响

• 批准号: 0444987
• 负责人: Paul Beier
• 金额: $ 25万
• 依托单位: Northern Arizona University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2005
• 资助国家: 美国
• 起止时间: 2005-05-01 至 2009-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0444987&HistoricalAwards=false
• 关键词: Bird; Predation; Forest; Insects; Growth

A trophic cascade occurs when a predator eats enough herbivores (plant-eating animals) to improve plant growth or to alter the structure of the plant community. Cascades have been documented in oceans and in places where wolves have been reintroduced. Although it is widely believed that forest birds benefit trees by eating insect pests of these trees, there are several reasons why birds might not drive a trophic cascade. For instance, plants might compensate for eaten leaves by rapidly producing new leaves, or birds might eat the same amount of insects as would have died due to other causes (weather, insect predators, starvation). In this research, investigators will test the hypothesis that predation of insects by birds benefits plants under some circumstances and will identify the conditions that affect the strength of the trophic cascade. The investigators will study the effects of insectivorous birds on cottonwood trees in the Southwestern United States. Cages will be built around whole trees to exclude birds from trees with high and low genetic susceptibility to insect pests. This will be the first study of its kind to measure growth responses of adult trees, and the first to measure seed production. By excluding birds from trees during different seasons, the study will determine how trees would respond to declines in resident birds (present year-round) or migratory birds (spring and summer only). By comparing the effect of birds to that of insecticides, the study will document the relative effectiveness of birds in insect control. The project will provide training for one PhD student and at least two undergraduates.

当捕食者吃到足够多的食草动物（植物动物）以改善植物生长或改变植物群落的结构时，就会发生营养级联。在海洋和重新引入狼的地方已经记录了级联反应。尽管人们普遍认为，森林鸟通过吃这些树木的害虫而使树木受益，但有几个原因使鸟类可能不会驱动营养的级联反应。例如，植物可能会通过快速生产新叶子来补偿所吃的叶子，或者鸟类可能会因其他原因（天气，昆虫捕食者，饥饿）而食用与昆虫相同数量的昆虫。在这项研究中，研究人员将检验以下假设：在某些情况下，鸟类对昆虫的捕食使植物受益，并确定影响营养级联反应强度的条件。研究人员将研究昆虫鸟对美国西南部杨木树的影响。笼子将围绕全树木建造，以将鸟类从遗传虫害易感性高和低的树木中排除。这将是衡量成年树的生长反应的第一个研究，也是第一个测量种子生产的研究。 通过在不同季节将鸟类排除在树木中，该研究将确定树木如何应对居民鸟类（目前全年）或迁徙鸟类（仅春季和夏季）的响应。 通过将鸟类与杀虫剂的作用进行比较，该研究将记录鸟类在昆虫控制中的相对有效性。该项目将为一名博士生和至少两名大学生提供培训。