RUI: Fluctuating Resources and Mechanisms of Invasibility Along the Prairie-Forest Border

[0208125]大卫：人们普遍认为，入侵生态学理论需要变得更加机械性、定量和预测性，需要实地实验和更好的模型来帮助实现这一目标。该项目的最初目标是测试最近的不可侵入性机制假设，并开发一个定量的经验模型，用于预测环境随时间变化的不可侵入性。假设检验表明，可入侵性与资源可获得性之间存在着一种机制关系，可入侵性的变化通常是由于来自居住植被的竞争强度的变化，而竞争强度的变化又由资源可获得性的波动引起。该项目将在位于明尼苏达州沙平原的原生草地环境中进行。因此，该项目的第二个目标是增加我们对半干旱环境中与草原和林地/草地过渡带相关的入侵动态的理解。这些目标将在一个由三个部分组成的研究中实现。在第一阶段，将利用来自实地实验的数据开发一个入侵的经验模型，在该模型中，将在实验入侵的地块中操纵资源可用性（水）的时间模式。在这一阶段，来自实地实验的数据也将用于直接测试波动资源可用性假设的预测。之所以选择水作为操纵资源，是因为先前对雪松溪幼苗建立的研究表明，草本植物和植物的建立成功与土壤水分条件最密切相关。在第二阶段，将使用现有的机械土壤水模型在各种气候（温度和降雨）数据集下生成研究地点的季节性土壤水剖面，这些数据集包括项目期间在研究地点记录的气候数据、该地区的历史气候数据以及如果气候变化未来可能发生的各种假设的温度和降水制度。在第三阶段，由机制模型产生的整个季节的水剖面将被用作入侵性经验模型的输入。由经验模型和机制模型整合产生的入侵性预测将与研究期间进行的单独现场实验获得的入侵性数据进行比较。如果综合模型的预测是成功的，那么它将与历史和假设的气候数据一起使用，以确定过去原生草原不可入侵性的年变率程度，以及如果温度和/或降水制度发生变化，不可入侵性在未来可能发生的变化程度。本研究的目的是促进生态学理论的发展和对特定环境的生态学认识。除了测试最近的不可侵入性机制理论外，该研究还将开发一种建模和预测可转移到其他环境的不可侵入性的方法。最近的证据表明，与其他生物群系相比，草地和老原野对降水波动的反应更灵敏，而草地和稀树草原等水资源有限的环境可能是受未来气候变化影响最大的一些生物群系。因此，通过在Cedar Creek的水有限的草地-森林交错带中测试一种特定的入侵机制理论，并最终开发出一种入侵模型，这项研究将有助于为预测和准备这些环境中全球环境变化可能造成的生态后果提供重要的知识库。

0208125DavisIt is widely agreed that invasion ecology theory needs to become more mechanistic,quantitative, and predictive and that field experiments and better models are required to helpaccomplish this goal. The initial goal of the proposed project is to test a recent mechanistichypothesis of invasibility and to develop a quantitative empirical model that can be used topredict the changing invasibility of an environment over time. The hypothesis tested proposesthat a mechanistic relationship exists between invasibility and resource availability, and thatchanges in invasibility are often due to changes in the competition intensity from residentvegetation, which in turn result from fluctuations in resource availability. This project will beconducted in a native grass environment located on a Minnesota sand plain. Thus, a second goalof the project is to increase our understanding of the invasion dynamics associated withgrasslands and woodland/grassland ecotones in semi-arid environments. These goals will beaccomplished in a study consisting of three parts.During the first stage, an empirical model of invasibility will be developed using datafrom a field experiment in which temporal patterns of resource availability (water) will bemanipulated in plots being experimentally invaded. During this stage, data from the fieldexperiments will also be used to directly test predictions of the fluctuating resource availabilityhypothesis. Water was selected as the resource to be manipulated because previous studies ofseedling establishment at Cedar Creek have shown that establishment success of herbaceous andplants was most strongly correlated with soil water conditions. During the second stage, anexisting mechanistic soil water model will be used to produce season-long soil water profiles atthe study site under a variety of climatological (temperature and rainfall) data sets, includingclimatological data recorded at the study site during the project, historical climatological data forthe region, and various hypothetical temperature and precipitation regimes that might occur inthe future if the climate changes. During the third stage, the season-long water profiles producedby the mechanistic model will be used as input for the empirical model of invasibility. Theinvasibility predictions produced by the integration of the empirical and mechanistic models willcompared to invasibility data obtained from a separate field experiment conducted during thestudy. If the integrated model is successful in its predictions, then it will be used with thehistorical and hypothetical climatological data to determine the extent of annual variability ininvasibility of native grasslands in the past, and the extent to which invasibility may change inthe future if temperature and/or precipitation regimes change.The goals of the proposed study are both to advance ecological theory and the ecologicalunderstanding of specific environments. In addition to testing a recent mechanistic theory ofinvasibility, the study will develop a method to model and predict invasibility that is intended tobe transferable to other environments. Recent evidence has shown that grasslands and old fieldsare more responsive to fluctuations in precipitation than other biomes and that water limitedenvironments such as grasslands and savannas are likely to be some of the biomes most affectedby future climate change. Thus, by testing a specific mechanistic theory of invasibility in thewater limited grassland-forest ecotone at Cedar Creek with an experimental study culminating inthe development of a model of invasibility, this study will contribute to the important pool ofknowledge that will be necessary to predict and prepare for the possible ecological consequencesof global environmental change in these environments.