Department of Ecology and Evolutionary Biology, Yale University, New Haven, Connecticut 06520, USA.
Ecology. 2009 Dec;90(12):3279-89. doi: 10.1890/08-1815.1.
In contrast to pulses in resource availability following disturbance events, many of the most pressing global changes, such as elevated atmospheric carbon dioxide concentrations and nitrogen deposition, lead to chronic and often cumulative alterations in available resources. Therefore, predicting ecological responses to these chronic resource alterations will require the modification of existing disturbance-based frameworks. Here, we present a conceptual framework for assessing the nature and pace of ecological change under chronic resource alterations. The "hierarchical-response framework" (HRF) links well-documented, ecological mechanisms of change to provide a theoretical basis for testing hypotheses to explain the dynamics and differential sensitivity of ecosystems to chronic resource alterations. The HRF is based on a temporal hierarchy of mechanisms and responses beginning with individual (physiological/metabolic) responses, followed by species reordering within communities, and finally species loss and immigration. Each mechanism is hypothesized to differ in the magnitude and rate of its effects on ecosystem structure and function, with this variation depending on ecosystem attributes, such as longevity of dominant species, rates of biogeochemical cycling, levels of biodiversity, and trophic complexity. Overall, the HRF predicts nonlinear changes in ecosystem dynamics, with the expectation that interactions with natural disturbances and other global-change drivers will further alter the nature and pace of change. The HRF is explicitly comparative to better understand differential sensitivities of ecosystems, and it can be used to guide the design of coordinated, cross-site experiments to enable more robust forecasts of contemporary and future ecosystem dynamics.
与干扰事件后资源可利用性的脉冲相反，许多最紧迫的全球变化，如大气二氧化碳浓度和氮沉积的升高，导致资源可利用性的慢性和常常是累积性的改变。因此，预测这些慢性资源改变对生态系统的影响将需要修改现有的基于干扰的框架。在这里，我们提出了一个评估慢性资源改变下生态变化的性质和速度的概念框架。“层次响应框架”（HRF）将改变的已有记录的生态机制联系起来，为测试假设提供了理论基础，以解释生态系统对慢性资源改变的动态和差异敏感性。HRF 基于机制和响应的时间层次，从个体（生理/代谢）响应开始，接着是群落内物种的重新排序，最后是物种的损失和迁入。每个机制都假设在其对生态系统结构和功能的影响的幅度和速度上有所不同，这种变化取决于生态系统属性，如优势物种的寿命、生物地球化学循环的速度、生物多样性水平和营养复杂性。总体而言，HRF 预测生态系统动态的非线性变化，预计与自然干扰和其他全球变化驱动因素的相互作用将进一步改变变化的性质和速度。HRF 是明确的比较性的，以便更好地理解生态系统的差异敏感性，并且可以用来指导协调的、跨站点实验的设计，以便更稳健地预测当代和未来的生态系统动态。
