Landscape Heterogeneity, Patch Connectivity, and Host-Parasitoid Population Dynamics

景观异质性、斑块连通性和寄主-寄主种群动态。自然栖息地的破碎化和丧失是一个严重的全球性问题。生态学家在理解栖息地碎片化或空间斑块化增加可能对捕食者-猎物种群的长期持久性产生的影响方面取得了重大进展。然而，大多数破碎化研究忽略了存在于斑块之间的植被覆盖（称为基质），通常假设基质对捕食者和猎物物种的运动和种群波动没有特征和中性。在现实中，矩阵是复杂且不断变化的。基质组成的任何变化都可能显著影响捕食者与猎物的相互作用。本提案概述了一个研究过程，旨在解决不同基质类型如何影响食草动物及其捕食者的运动和人口波动。在美国大平原的草原上，分布在离散斑块上的飞虱（Prokelisia crocea）和寄生蜂（Anagrus columbi）构成了这类研究的理想系统。这个提议的关键是一个相对大规模的实地实验，旨在通过在两种主要基质类型（泥滩或外来草种雀间）中的任何一种中嵌入网草斑块来改变飞虱和黄蜂在斑块之间移动的能力（即斑块连通性）。通过重新捕获荧光标记的个体，评估昆虫的迁出、迁移、空间传播模式和斑块内分布。该实验还将在3个空间尺度和6代范围内进行，以提供基质操作对寄主的影响以及斑块间和时间间密度波动的信息。在野外的捕食者-猎物种群研究中，从未对斑块结构和基质进行过操纵。作为田间试验的补充，还将进行试验，以确定飞虱和黄蜂依赖基质的运动模式的行为基础。最后，基于上述研究得出的信息，将开发一个模拟模型，以评估栖息地破碎化和退化（例如，景观矩阵的变化）对捕食者-猎物相互作用长期持续的影响。美国国家科学基金会（NSF） DEB-9973789基金的更新研究结果将为研究异质性景观对捕食者-猎物相互作用的影响提供关键和急需的信息，并有望催化更广泛的研究捕食者-猎物相互作用的方法。这项研究也对关注保护区连通性的保护项目产生了广泛的影响：一个促进扩散的矩阵（即一个高质量的矩阵）可能起到与垫脚石或走廊相同的作用。最后，这项研究可能会直接影响到害虫管理项目的成功，这些项目采用有目的地修改基质的策略（例如，通过间作、梯田或让一些田地休耕）。了解这些变化对害虫和天敌运动和相互作用的影响，可能对制定成功的害虫防治计划至关重要。

Landscape heterogeneity, patch connectivity, and host-parasitoid population dynamicsNSF Ecological Studies Grant (DEB-0211359)September 1, 2002 - August 31, 2005 The fragmentation and loss of natural habitats is a dire world-wide problem. Ecologists have made significant in-roads toward understanding the impact that increased habitat fragmentation or spatial patchiness might have on the long-term persistence of predator-prey populations. However, most fragmentation studies have disregarded the vegetational cover that exists between patches (known as the matrix), generally assuming that the matrix is featureless and neutral to the movements and population fluctuations of both predator and prey species. In reality, the matrix is complex and ever-changing. Any alteration in matrix composition may significantly impact how predators interact with their prey. This proposal outlines a course of study designed to address how different matrix types influence the movement and population fluctuations of an herbivore and its predator. The planthopper, Prokelisia crocea, and the parasitoid wasp, Anagrus columbi, which are distributed among discrete patches of prairie cordgrass in the Great Plains of the United States form an ideal system for this type of study. The crux of this proposal is a relatively large-scale field experiment that is designed to alter the ability of planthoppers and wasps to move among patches (i.e., patch connectivity) by embedding cordgrass patches in either of two dominant matrix types (mudflat or the exotic grass species brome). Emigration, immigration, the pattern of spatial spread, and the within-patch distribution of insects will be assessed from the recapture of fluorescent-marked individuals. The experiment also will be carried out over 3 spatial scales and 6 generations to provide information on the effect of the matrix manipulation on parasitism and density fluctuations among patches and over time. Never before has the patch structure and matrix been manipulated in predator-prey population studies in the field. As a complement to this field experiment, trials will also be conducted to determine the behavioral basis for matrix-dependent movement patterns of the planthopper and wasp. Finally, based on information derived in the above studies, a simulation model will be developed with the goal of evaluating the impact of habitat fragmentation and degradation (e.g., changes in the landscape matrix) on the long-term persistence of predator-prey interactions. Results from this renewal of NSF grant DEB-9973789 should provide critical and much needed information on the effects of heterogeneous landscapes on predator-prey interactions, and hopefully catalyze a broader approach to studies of predator-prey interactions. This research also has broad ramifications for conservation programs that are interested in the connectivity of reserves: a matrix that facilitates dispersal (i.e., a high-quality matrix) may serve a function identical to that of stepping stones or corridors. Finally, this research may have a direct bearing on the success of pest management programs that employ strategies that purposely modify the matrix (e.g., through inter-cropping, terracing, or leaving some fields fallow). Knowledge of the effect of these changes on pest and natural enemy movement and interactions may be critical to developing a successful pest-control program.