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

人们普遍认为，入侵生态学理论需要变得更加机械化、定量化和预测化，需要通过田间试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一个机制假设的入侵性，并开发一个定量的经验模型，可用于预测随着时间的推移不断变化的环境的入侵性。假设检验提出入侵性与资源可利用性之间存在一种机制关系，入侵性的变化往往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是资源可利用性波动的结果。该项目将在明尼苏达州的一个沙地平原上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草原和林地/草原交错带的入侵动力学的理解。这些目标将在一项由三个部分组成的研究中实现。在第一阶段，将利用实地实验的数据建立一个入侵性的经验模型，在该实验中，将在实验入侵的地块中模拟资源可用性（水）的时间模式。在这一阶段，来自现场实验的数据也将被用来直接检验波动资源可用性假设的预测。水被选为要操纵的资源，因为以前的研究表明，在雪松溪建立幼苗的成功草本植物和植物是最强烈的土壤水分条件相关。在第二阶段，将利用现有的土壤水分机械模型，根据各种气候（温度和降雨量）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，以及如果气候发生变化，未来可能出现的各种假设温度和降雨状况，在研究地点生成季节性土壤水分剖面。在第三阶段，机械模型产生的季节性水分剖面将用作入侵经验模型的输入。通过整合经验模型和机械模型产生的侵袭性预测将与研究期间进行的单独现场实验获得的侵袭性数据进行比较。如果综合模型的预测是成功的，那么它将被用来与历史和假设的气候数据，以确定在过去的天然草地的年变化的入侵程度，以及在何种程度上入侵可能会改变在未来，如果温度和/或降水制度的变化。除了测试最近的机械理论的侵入性，该研究将开发一种方法来建模和预测的侵入性，旨在转移到其他环境。最近的证据表明，草原和老田地比其他生物群系对降水量波动的反应更敏感，而且像草原和稀树草原这样的水有限的植被很可能是受未来气候变化影响最大的生物群系。因此，通过测试一个特定的机械理论的入侵在水有限的草原森林交错带在雪松溪的实验研究最终在发展的模型的入侵，这项研究将有助于重要的知识库，将是必要的预测和准备可能的生态后果，全球环境变化在这些环境中。

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.