The Joint Effects of Herbivory and Competition Upon Plant Communities

这项由奥斯汀得克萨斯大学的诺玛·福勒博士提出的建议是研究放牧和植物间竞争对植物群落结构的综合影响。放牧对植物的影响不仅限于落叶的影响，还包括践踏、尿液和粪便沉积的影响。不会对这些次要影响进行调查。最初，调查将集中在落叶的影响上。然而，每个田间试验都将包括(围栏)剪裁处理和(非围栏)放牧处理以及(围栏)对照；剪裁处理和放牧处理之间的差异可能是由于这些次要影响，或者可能是为了区分机械剪裁和动物下巴的动作。剪裁处理和放牧处理之间没有差异将支持零假设，即在这个系统中，放牧的影响在很大程度上限于组织去除的直接影响。这些实验中将包括修剪处理，不仅是为了验证这一假说，还因为放牧的效果也是动物对不同物种、大小、生理和发育状态、周围植被等植物的偏好的函数。竞争和落叶之间的明显交互效应可能来自偏好的影响，而偏爱实际上并不存在。将对偏好进行估计，并将结果用于指示适当的附加实验治疗。这项工作具有许多内在的生态利益，但其直接的实用价值在于它对于理解植物群落的维护，特别是在营养贫乏的草原、稀树草原等过度放牧的情况下的重要性。

This proposal by Dr. Norma Fowler of the University of Texas, Austin is to examine the combined influences of grazing and interplant competition on plant community structure. The effects of grazing upon plants are not limited to the effects of defoliation, but include the effects of trampling, and urine and dung deposition. Investigation of these secondary effects will not be done. Initially, the investigation will concentrate upon the effects of defoliation. However, each of the field experiments will include both a (fenced) clipping treatment and an (unfenced) grazing treatment as well as a (fenced) control; differences between the clipping and grazing treatments may be due to these secondary effects, or perhaps to differentiate between mechanical clipping and the action of an animal's jaw. An absence of differences between the clipping and grazing treatments will support the null hypothesis that in this system the effects of grazing are largely limited to the direct effects of tissue removal. A clipping treatment will be included in these experiments, not only to test this hypothesis, but also because the effects of grazing are also a function of animal preferences for plants of different species, sizes, physiological and developmental states, surrounding vegetation, and so on. An apparent interaction effect between competition and defoliation can arise from the effects of preference, when none is actually present. Estimates of preference will be made and the results used to indicate appropriate additional experimental treatments. This work has much intrinsic, ecological interests, but its immediate practical value is in its importance for understanding plant community maintenance, especially in over-grazing situations in nutrient poor prairies, savannas, etc.