Collins Sean E, Matter Stephen F, Buffam Ishi, Flotemersch Joseph E
Department of Biological Sciences, University of Cincinnati, Cincinnati, Ohio 45221 USA.
National Exposure Research Laboratory, U.S. Environmental Protection Agency, Cincinnati, Ohio 45220 USA.
Ecosphere. 2018 Nov;9(11). doi: 10.1002/ecs2.2481. Epub 2018 Nov 16.
Many conceptual syntheses in ecology and evolution are undergirded by either a patch- or continuum-based model. Examples include gradualism and punctuated equilibrium in evolution, and edge effects and the theory of island biogeography in ecology. In this study, we sought to determine how patch- or continuum-based analyses could explain variation in concentrations of stream macronutrients and system metabolism, represented by measures of productivity and respiration rates, at the watershed scale across the Kanawha River Basin, USA. Using Strahler stream order (SSO; continuum) and functional process zone (FPZ; patch) as factors, we produced statistical models for each variable and compared model performance using likelihood ratio tests. Only one nutrient (i.e., ) responded better to patch-based analysis. Both models were significantly better than a null model for ecosystem respiration; however, neither outperformed the other. Importantly, in most cases, a combination model, including both SSO and FPZ, best described observed variation in the system. Our findings suggest that several patch- and continuum-based processes may simultaneously influence the concentration of macronutrients and system metabolism. Nutrient spiral- ing along a continuum and the patch mosaic of land cover may both alter macronutrients, for example. Similarly, increases in temperature and discharge associated with increasing SSO, as well as the differences in light availability and channel morphology associated with different FPZs, may influence system metabolism. For these reasons, we recommend a combination of patch- and continuum-based analyses when modeling, analyzing, and interpreting patterns in stream ecosystem parameters.
生态学和进化领域的许多概念综合都基于斑块或连续体模型。例如进化中的渐变论和间断平衡论，以及生态学中的边缘效应和岛屿生物地理学理论。在本研究中，我们试图确定基于斑块或连续体的分析如何解释美国卡诺瓦河流域流域尺度上河流大量营养素浓度和系统代谢的变化，系统代谢以生产力和呼吸速率来衡量。我们将斯特拉勒河流等级（SSO；连续体）和功能过程区（FPZ；斑块）作为因素，为每个变量建立统计模型，并使用似然比检验比较模型性能。只有一种营养素（即 ）对基于斑块的分析反应更好。两个模型在解释生态系统呼吸方面都显著优于零模型；然而，没有一个模型比另一个表现得更好。重要的是，在大多数情况下，一个包括SSO和FPZ的组合模型能最好地描述系统中观察到的变化。我们的研究结果表明，几个基于斑块和连续体的过程可能同时影响大量营养素的浓度和系统代谢。例如，沿着连续体的养分螺旋和土地覆盖的斑块镶嵌都可能改变大量营养素。同样，与SSO增加相关的温度和流量增加，以及与不同FPZ相关的光照可用性和河道形态差异，可能影响系统代谢。出于这些原因，我们建议在对河流生态系统参数的模式进行建模、分析和解释时，结合基于斑块和连续体的分析。
