Theoretical Frameworks for Ecological Dynamics Subject to Stoichiometric Constraints

所有的生物都是由多种化学元素组成的，比如碳、氮和磷。最近在生态化学计量学领域的研究强调了化学成分相对丰度的生态重要性，已知化学成分在物种和跨营养水平之间差异很大。然而，直到最近，生态学的大多数理论研究都忽略了这种化学异质性的来源和后果。研究者和他的同事进行生态化学计量学的理论研究。他们开发了一个相对较新的理论框架预测动力学明确纳入化学计量约束。这个基础模型涉及到我们熟悉的罗森茨威格-麦克阿瑟方程的化学计量对应，其中资源物种的有效承载能力和消费物种的转移效率受到化学计量原理的约束。在这些方程中引入化学计量考虑（这里类似于“食品质量”），可以考虑丰富的生态现实动态，包括当资源丰富但质量差时消费物种的确定性灭绝。他们从五个不同的方向扩展了这个模型，以探索生态现实（即复杂性），其考虑在其他非化学计量环境中已被证明具有启发性。具体来说，他们分析了1)多营养模型的动态；2)多种消费物种共享资源的营养复杂模型；3)作为陆地生态系统现实组成部分的养分循环的时间延迟；4)生境异质性和消费者分散性的两个斑块模型；5)青少年和成人消费者营养需求不同的年龄结构模型。该项目旨在为新兴的生态化学计量学实证研究提供严谨的分析基础。包括人类在内的所有生物，都是由大致相同的一组基本构件构成的，这些基本构件包括碳(C)、氮(N)、磷(P)等化学元素，以及其他几十种少量的化学元素。然而，不同的生物体在其生物量中含有不同比例的这些关键元素，因此必须从其环境中不同程度地提取这些元素。在许多情况下，环境不能提供这些关键的营养元素的丰度和比例，这是生物体生长和繁殖的最佳选择。因此，生命的化学环境可能会限制生物体在各种情况下的成功。在这个项目中，研究人员使用数学模型来模拟天然食物网中多种化学元素的流动，以更好地了解生物对多种化学元素的需求如何在生物和非生物世界之间建立关键反馈。这项工作之所以重要，有两个原因。首先，它可以提供对化学元素如何在食物网中移动的更好的基本理解。其次，提高对营养物质如何在环境中移动以及如何用数学工具模拟这些运动的基本知识，可能有助于预测和管理自然和人类主导的生态系统，包括那些受人类活动的营养输入（例如肥料和污水的Nand P输入）或全球变化（例如大气二氧化碳增加对环境中C和营养流动的影响）影响的生态系统。

Kuang0077790 All organisms are composed of multiple chemical elementssuch as carbon, nitrogen, and phosphorus. Recent research in thearea known as ecological stoichiometry has highlighted theecological importance of the relative abundance of chemicalconstituents, known to vary considerably among species and acrosstrophic levels. However, most theoeretical studies in ecologyhave until very recently ignored the sources and consequences ofthis chemical heterogeneity. The investigator and his colleaguesundertake theoretical investigations of ecological stoichiometry.They develop a relatively new theoretical framework forecological dynamics that explicitly incorporates stoichiometricconstraints. This base model involves a stoichiometriccounterpart of the familiar Rosenzweig-MacArthur equations inwhich the effective carrying capacity of the resource species andthe transfer efficiency of the consumer species are constrainedby stoichiometric principles. Introduction of stoichiometricconsiderations in these equations (here, akin to "food quality")allows for a rich array of ecologically realistic dynamics,including deterministic extinction of the consumer species whenresources are abundant but of poor quality. They expand thismodel in five different directions, to explore ecologicalrealities (i.e., complications) whose consideration has provedilluminating in other, non-stoichiometric settings. Specifically,they analyze the dynamics of 1) a multi-nutrient model; 2)trophically complex models in which multiple consumer speciesshare a resource; 3) time delays in nutrient recycling that are arealistic component of terrestrial ecosystems; 4) two patchmodels featuring habitat heterogeneity and dispersal of theconsumer; and 5) age structured models in which juvenile andadult consumers differ in their nutrient requirements. Theproject aims to provide an analytically rigorous foundation forburgeoning empirical research into ecological stoichiometry. All living things, including humans, are constructed ofapproximately the same set of basic building blocks, chemicalelements such as carbon (C), nitrogen (N), phosphorus (P), andseveral dozen more in smaller amounts. However, differentorganisms contain different proportions of these key elements intheir biomass and thus must extract these elements from theirenvironment to differing degrees. In many situations, theenvironment does not provide these key nutrient elements in theabundance and proportions that are optimal for organism growthand reproduction. Thus, the chemical environment of life may setlimits on the success of organisms in various situations. In thisproject the investigators use mathematical models to simulate theflow of multiple chemical elements in natural food webs to betterunderstand how the requirements of living things for multiplechemical elements establish key feedbacks between the living andnon-living world. This work is important for two reasons. First,it may provide a better fundamental understanding of how chemicalelements move through food webs. Second, improved fundamentalknowledge of how nutrients move in the environment and how tosimulate those movements with mathematical tools may help predictand manage natural and human-dominated ecosystems, includingthose affected by nutrient inputs from human activities (e.g. Nand P inputs from fertilizer, sewage) or by global change (e.g.effects of increased atmospheric carbon dioxide on C and nutrientflow in the environment).