Global environmental change and sustainability science increasingly recognize the need to address the consequences of changes taking place in the structure and function of the biosphere. These changes raise questions such as: Who and what are vulnerable to the multiple environmental changes underway, and where? Research demonstrates that vulnerability is registered not by exposure to hazards (perturbations and stresses) alone but also resides in the sensitivity and resilience of the system experiencing such hazards. This recognition requires revisions and enlargements in the basic design of vulnerability assessments, including the capacity to treat coupled human-environment systems and those linkages within and without the systems that affect their vulnerability. A vulnerability framework for the assessment of coupled humanenvironment systems is presented. R esearch on global environmental change has significantly improved our understanding of the structure and function of the biosphere and the human impress on both (1). The emergence of ''sustainability science'' (2-4) builds toward an understanding of the human-environment condition with the dual objectives of meeting the needs of society while sustaining the life support systems of the planet. These objectives, in turn, require improved dialogue between science and decision making (5-8). The vulnerability of coupled human-environment systems is one of the central elements of this dialogue and sustainability research (6, 9-11). It directs attention to such questions as: Who and what are vulnerable to the multiple environmental and human changes underway, and where? How are these changes and their consequences attenuated or amplified by different human and environmental conditions? What can be done to reduce vulnerability to change? How may more resilient and adaptive communities and societies be built?Answers to these and related questions require conceptual frameworks that account for the vulnerability of coupled human-environment systems with diverse and complex linkages. Various expert communities have made considerable progress in pointing the way toward the design of these frameworks (10, 11). These advances are briefly reviewed here and, drawing on them, we present a conceptual framework of vulnerability developed by the Research and Assessment Systems for Sustainability Program (http:͞͞sust.harvard.edu) that produced the set of works in this Special Feature of PNAS. The framework aims to make vulnerability analysis consistent with the concerns of sustainability and global environmental change science. The case study by Turner et al. (12) in this issue of PNAS illustrates how the framework informs vulnerability assessments. The Emergence of Vulnerability AnalysisApproaches to and Composition of Vulnerability. Vulnerability is the degree to which a system, subsystem, or system component is likely to experience harm due to exposure to a hazard, either a perturbation or stress͞stressor. i This definition and the concept it addresses are not new (13); they ...

Abstract. A pelagic food web model was formulated with the goal of developing a quantitative understanding of the relationship between total production, export production, and environmental variables in marine ecosystems. The model assumes that primary production is partitioned through both large and small phytoplankton and that the food web adjusts to changes in the rate of allochthonous nutrient inputs in a way that maximizes stability, i.e., the ability of the system to return to steady state following a perturbation. The results of the modeling exercise indicate that ef ratios, defined as new production/total production = export production/total production, are relatively insensitive to total production rates at temperatures greater than -25øC and lie in the range 0.1-0.2. At moderate to high total production rates, ef ratios are insensitive to total production and negatively correlated with temperature. The maximum ef ratios are -0.67 at high rates of production and temperatures of 0 ø-10øC. At temperatures less than -20øC, there is a transition from low ef ratios to relatively high ef ratios as total production increases from low to moderate values. This transition accounts for the hyperbolic relationship often presumed to exist between ef ratios and total production. At low rates of production the model predicts a negative correlation between production and ef ratios, a result consistent with data collected at station ALOHA (22ø45'N, 158øW) in the North Pacific subtropical gyre. The predictions of the model are in excellent agreement with results reported from the Joint Global Ocean Flux Study (JGOFS) and from other field work. In these studies, there is virtually no correlation between total production and ef ratios, but temperature alone accounts for 86% of the variance in the ef ratios. Model predictions of the absolute and relative abundance of autotrophic and heterotrophic

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Uptake rate of nitrate and ammonium was studied as a function of nitrate or ammonium concentration with cultures of 16 species of marine phytoplankton.Half-saturation constants (the concentration supporting an uptake rate one-half the maximum rate) were computed as a measure of the ability of a species to use low levels of nitrate and ammonium.

Whales as ecosystem engineers J Roman et al. 378www.frontiersinecology.org

The r-TEG data was clinically superior to results from 5 CCTs. In addition, r-TEG identified patients with an increased risk of early RBC, plasma and platelet transfusions, and fibrinolysis. Admission CCTs can be replaced with r-TEG.

The vulnerability framework of the Research and Assessment Systems for Sustainability Program explicitly recognizes the coupled human-environment system and accounts for interactions in the coupling affecting the system's responses to hazards and its vulnerability. This paper illustrates the usefulness of the vulnerability framework through three case studies: the tropical southern Yucatá n, the arid Yaqui Valley of northwest Mexico, and the pan-Arctic. Together, these examples illustrate the role of external forces in reshaping the systems in question and their vulnerability to environmental hazards, as well as the different capacities of stakeholders, based on their access to social and biophysical capital, to respond to the changes and hazards. The framework proves useful in directing attention to the interacting parts of the coupled system and helps identify gaps in information and understanding relevant to reducing vulnerability in the systems as a whole.