Schmidt Kenneth A, Ostfeld Richard S
Department of Biological Sciences, Texas Tech University, MS 3131, Lubbock, Texas 79409, USA.
Ecology. 2008 Mar;89(3):635-46. doi: 10.1890/07-0199.1.
Some of the clearest examples of the ramifying effects of resource pulses exist in deciduous forests dominated by mast-producing trees, such as oaks, beech, and hornbeam. Seed production in these forests represents only the first of several pulsed events. Secondary pulses emerge as mast-consuming small rodents numerically respond to seed production and tertiary pulses emerge as generalist predators numerically respond to rodents. Raptors may also respond behaviorally (i.e., diet shifts) to subsequent crashes in small rodents following the crash phase in seed production. In oak-dominated forest in the Hudson Valley, New York, these various pulse and crash phases act synergistically, although not simultaneously, to influence thrush population dynamics through predation on nests, juveniles, and adults. As a consequence, factors limiting population growth rate and their age-specific action vary as a function of past acorn production. We highlight these interactions based on our eight-year study of thrush demography, acorn production, and small mammal abundance coupled with information on regional adult thrush population trends from the Breeding Bird Survey. We use these data sets to demonstrate the sequence of primary to tertiary pulses and how they influence breeding thrush populations. To extend our discussion beyond masting phenomena in the eastern United States, we briefly review the literature of alternative avian prey within pulsed systems to show (1) numerical and behavioral responses by generalist predators are ubiquitous in pulsed systems, and this contributes to (2) variability in reproduction and survivorship of avian prey linked to the underlying dynamics of the pulse. We conclude by exploring the broad consequences of cascading resource pulses for alternative prey based upon the indirect interaction of apparent competition among shared prey and the nature of temporal variability on populations.
资源脉冲的分支效应最明显的一些例子存在于以产坚果树木为主的落叶林中，比如橡树、山毛榉和鹅耳枥。这些森林中的种子生产只是一系列脉冲事件中的第一个。随着以坚果为食的小型啮齿动物数量对种子生产做出反应，二级脉冲出现；随着食性广泛的捕食者数量对啮齿动物做出反应，三级脉冲出现。猛禽也可能在种子生产的崩溃阶段之后，对小型啮齿动物数量随后的减少做出行为反应（即饮食转变）。在纽约哈德逊河谷以橡树为主的森林中，这些不同的脉冲和崩溃阶段协同作用（尽管不是同时发生），通过捕食巢穴、幼鸟和成鸟来影响画眉鸟的种群动态。因此，限制种群增长率的因素及其特定年龄的作用会随着过去橡子产量的变化而变化。基于我们对画眉鸟种群统计学、橡子产量和小型哺乳动物数量的八年研究，以及繁殖鸟类调查中关于区域成年画眉鸟种群趋势的信息，我们突出了这些相互作用。我们利用这些数据集来展示从一级脉冲到三级脉冲的序列，以及它们如何影响繁殖画眉鸟种群。为了将我们的讨论扩展到美国东部以外的产果现象，我们简要回顾了脉冲系统中替代鸟类猎物的文献，以表明：（1）食性广泛的捕食者的数量和行为反应在脉冲系统中普遍存在，这导致了（2）与脉冲的潜在动态相关的鸟类猎物繁殖和生存的变异性。我们通过探讨基于共享猎物之间明显竞争的间接相互作用以及种群时间变异性的性质，级联资源脉冲对替代猎物的广泛影响来得出结论。
