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Does society benefit from encouraging or discouraging private infectious disease-risk mitigation? Private individuals routinely mitigate infectious disease risks through the adoption of a range of precautions, from vaccination to changes in their contact with others. Such precautions have epidemiological consequences. Private disease-risk mitigation generally reduces both peak prevalence of symptomatic infection and the number of people who fall ill. At the same time, however, it can prolong an epidemic. A reduction in prevalence is socially beneficial. Prolongation of an epidemic is not. We find that for a large class of infectious diseases, private risk mitigation is socially suboptimal—either too low or too high. The social optimum requires either more or less private mitigation. Since private mitigation effort depends on the cost of mitigation and the cost of illness, interventions that change either of these costs may be used to alter mitigation decisions. We model the potential for instruments that affect the cost of illness to yield net social benefits. We find that where a disease is not very infectious or the duration of illness is short, it may be socially optimal to promote private mitigation effort by increasing the cost of illness. By contrast, where a disease is highly infectious or long lasting, it may be optimal to discourage private mitigation by reducing the cost of disease. Society would prefer a shorter, more intense, epidemic to a longer, less intense epidemic. There is, however, a region in parameter space where the relationship is more complicated. For moderately infectious diseases with medium infectious periods, the social optimum depends on interactions between prevalence and duration. Basic reproduction numbers are not sufficient to predict the social optimum.

In a rapidly changing world, the question concerning the “right” balance between modeling and empirical work has never been more important. But achieving that balance is not just a matter of student training—it involves examining the incentives in, and structures of, the discipline as a whole.

Highly pathogenic avian influenza (HPAI) H5N1 has led to the death or destruction of millions of domesticated and wild birds and caused hundreds of human deaths worldwide. As with other HPAIs, H5N1 outbreaks among poultry have generally been caused by contact with infected migratory waterfowl at the interface of wildlands and human-dominated landscapes. Using a case–control epidemiological approach, we analyzed the relation between habitat protection and H5N1 outbreaks in China from 2004 to 2017. We found that while proximity to unprotected waterfowl habitats and rice paddy generally increased outbreak risk, proximity to the most highly protected habitats (e.g., Ramsar-designated lakes and wetlands) had the opposite effect. Protection likely involves two mechanisms: the separation of wild waterfowl and poultry populations and the diversion of wild waterfowl from human-dominated landscapes toward protected natural habitats. Wetland protection could therefore be an effective means to control avian influenza while also contributing to avian conservation. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s13280-019-01238-2) contains supplementary material, which is available to authorized users.

Three interrelated world trends may be exacerbating emerging zoonotic risks: income growth, urbanization, and globalization. Income growth is associated with rising animal protein consumption in developing countries, which increases the conversion of wild lands to livestock production, and hence the probability of zoonotic emergence. Urbanization implies the greater concentration and connectedness of people, which increases the speed at which new infections are spread. Globalization-the closer integration of the world economy-has facilitated pathogen spread among countries through the growth of trade and travel. High-risk areas for the emergence and spread of infectious disease are where these three trends intersect with predisposing socioecological conditions including the presence of wild disease reservoirs, agricultural practices that increase contact between wildlife and livestock, and cultural practices that increase contact between humans, wildlife, and livestock. Such an intersection occurs in China, which has been a "cradle" of zoonoses from the Black Death to avian influenza and SARS. Disease management in China is thus critical to the mitigation of global zoonotic risks.

Demands for ecosystem service assessments are growing around the world. However, management applications remain limited in part because we lack measurements linking ecosystem characteristics (ecosystem structure and processes) to final ecosystem services. Policymakers need marginal values, changes in final ecosystem services (direct link to human welfare) relative to additional units of ecosystem characteristics (∆final ecosystem services/∆ecosystem characteristics) to assess tradeoffs. Progress, however, has been slow due to confusion on ecological production functions (EPFs) in ecology. Here, we apply a new interdisciplinary approach to craft EPFs to evaluate four ecosystem services using the Yongding River Green Ecological Corridor as our case study. The Yongding Corridor is Beijing's largest, most expensive green infrastructure project (~ $2.5 billion USD), constructed as a network of seven artificial lakes and wetlands. The Beijing Government wants the Yongding Corridor to improve four ecosystem services: (1) water storage, (2) local climate regulation, (3) water purification, and (4) aesthetics. We first worked with stakeholders to determine final ecosystem service levels and then used the Variable Infiltration Capacity model to estimate key ecosystem processes from the designed lakes and wetlands. We coupled the modeling with ecological field data and social surveys to create EPFs. We evaluated the ecosystem services by calculating shortfalls and then determined synergies and tradeoffs to identify actions for reducing shortfalls. We found the Yongding Corridor is meeting desired levels for aesthetics, but incurred shortfalls on the remaining services. To obtain the desired services, we recommend managers: (1) maintain inflow rates and/or make the lakes deeper to reduce water loss rates; (2) improve water quality—wetlands have high nutrient retention, but nutrient loads must be reduced; and (3) plant shade trees since evaporative cooling from the lakes and wetlands is having no measurable impact on human comfort. Results indicate the absence of ecosystem functions in landscape design led to shortfalls, but solutions require coupling green and built infrastructure to obtain multi‐functionality. Managers found marginal values useful for clarifying connections, which led to adaptive policy changes for improving green infrastructure.

Governments worldwide are recognising ecosystem services as an approach to address sustainability challenges. Decision-makers need credible and legitimate measurements of ecosystem services to evaluate decisions for trade-offs to make wise choices. Managers lack these measurements because of a data gap linking ecosystem characteristics to final ecosystem services. The dominant method to address the data gap is benefit transfer using ecological data from one location to estimate ecosystem services at other locations with similar land cover. However, benefit transfer is only valid once the data gap is adequately resolved. Disciplinary frames separating ecology from economics and policy have resulted in confusion on concepts and methods preventing progress on the data gap. In this study, we present a 10-step approach to unify concepts, methods and data from the disparate disciplines to offer guidance on overcoming the data gap. We suggest: (1) estimate ecosystem characteristics using biophysical models, (2) identify final ecosystem services using endpoints and (3) connect them using ecological production functions to quantify biophysical trade-offs. The guidance is strategic for public policy because analysts need to be: (1) realistic when setting priorities, (2) attentive to timelines to acquire relevant data, given resources and (3) responsive to the needs of decision-makers.

Sustainable development requires that per capita inclusive wealth—produced, human, and natural capital—does not decline over time. We investigate the impact of changes in nitrogen on inclusive wealth. There are two sides to the nitrogen problem. Excess use of nitrogen in some places gives rise to N-pollution, which can cause environmental damage. Insufficient replacement of nitrogen in other places gives rise to N-depletion, or loss of nutrient stocks. Neither is explicitly accounted for in current wealth measures, but both affect wealth. We calculate an index of net N-replacement, and investigate its relationship to wealth. In countries with low levels of relative N-loss, we find that the uncompensated loss of soil nitrogen in poorer countries is associated with declining rates of growth of inclusive per capita wealth. What is less intuitive is that increasing fertilizer application in both rich and poor countries can increase per capita inclusive wealth.

One of the most important services provided by forests is the control of erosion. We investigated the value of forest cover in protecting water quality in five urban lakes around Prescott, AZ. We first estimated the role of forest cover in regulating sediment loadings into each lake via a sediment delivery model. We then used 8301 single-family residential property transactions that occurred between 2002 and 2005 in Prescott, AZ, to estimate a hedonic price function. This yielded an estimate of the marginal willingness-to-pay (MWTP) for avoiding 1 t of sediment per lake-acre, from which we were able to infer the marginal willingness to pay for the erosion control services associated with a 10% change in current canopy cover. We found that the marginal value of the erosion control services of forest cover varies widely across the watersheds depending on the accessibility of affected lakes, the current level of canopy cover, and the number and value of affected residential properties among other factors.

After the collective failure to achieve the Convention on Biological Diversity's (CBD's) 2010 target to substantially reduce biodiversity losses, the CBD adopted a plan composed of five strategic goals and 20 “SMART” (Specific, Measurable, Ambitious, Realistic, and Time-bound) targets, to be achieved by 2020. Here, an interdisciplinary group of scientists from DIVERSITAS – an international program that focuses on biodiversity science – evaluates these targets and considers the implications of an ecosystem-services-based approach for their implementation. We describe the functional differences between the targets corresponding to distinct strategic goals and identify the interdependency between targets. We then discuss the implications for supporting research and target indicators, and make several specific suggestions for target implementation.

It has long been recognized that major drivers of biodiversity loss include both the harvest of wild species and the conversion of habitat for productive purposes. Land that is converted may or may not be lost as habitat for many species. In some cases, monoculture production for example, land conversion reduces the number niches and hence the level of biodiversity. In other cases, it has the opposite effect. We address the problem of anthropogenic biodiversity change due to the effects of both harvest rates and land use decisions on landscape heterogeneity. If the optimal structure of the landscape is extremely homogeneous, forces of competitive exclusion will lead to a single surviving species. If it is extremely heterogeneous, multiple species will coexist, with each species exclusively dominating the patch type to which it is best suited. Where changes in biodiversity due to changes in landscape heterogeneity are not taken into account in land use decisions, they are external effects of those decisions. We identify measures of these effects.

Cultivation of agave was common in pre-Hispanic northern Mexico and the American Southwest, and scholars generally accept that it was a strategy to ensure food supply during years of drought when the maize crop failed. Some even suggest that incorporating agave cultivation make large, nucleated settlements possible in arid northern Mexico ca. 500–900 CE. Yet the environmental circumstances under which farmers could reasonably expect such a strategy to decrease the chances of agricultural failure are not well understood. We explore the potential of this crop complementarity by assessing the risk of famine-induced migration events in different idealized environmental settings. We use Monte Carlo simulation to analyze a simple discrete-time, age-structured stochastic model for maize and agave agroecology, deriving the climatological conditions under which agave could have significantly reduced the probability of short- and long-term famine events. Investments in agave production made the most sense where average annual rainfall was between the levels that would ensure maximum maize yield and those that would mean loss of the maize crop due to drought-related mortality. Cultivating agave had little impact on famine risk at high (maize yields sufficient) and low (failure of both maize and agave) rainfall levels. Perhaps more surprisingly, it had its highest impact at moderate rainfall levels when variance in rainfall was relatively low. While a higher variance in rainfall increased the number of ‘good’ years for maize—where production would exceed demand and allow for storage—it also increased the probability of simultaneous failures in both agave and maize production. These findings are difficult to apply to specific times and places in the past, because rainfall distribution in complex, environments change, and it is difficult to take all relevant human interventions into account. The analysis does, however, offer support for the proposition that agave cultivation could have significantly enhanced survival probabilities of large, nucleated settlements in certain circumstances. It remains for further study to identify such circumstances more precisely geographically and temporally.

Today’s worldwide expansion of dry land cities consumes cultivated and native ecosystems, providing laboratories for investigating imprints of former land use in places where people now live. Around Phoenix, USA, we compared soil nutrient pools in residential yards converted from farms with nutrient pools in yards developed on native desert. Organic matter, carbon (C), nitrogen (N), and soluble ions were 42-fold greater in yards that were previously agrarian than in yards that were not. These pools remain elevated 40 years after land conversion to residential use. Present N accumulation (1.5gm � 2 yr � 1 ) is not affected by prior land use, suggesting that rates of residential fertilizer application and retention are not affected by antecedent soil fertility. Bioavailable, inorganic phosphorus (Pav) is elevated in soil with a recent agrarian past, but this signal disappears after 10–30 years of residential use owing to an accumulation of Pav in never-farmed yards. Our results indicate a ‘direct agrarian legacy,’ wherein agrarian amendment of nutrient pools endures urbanization, more so than an ‘indirect legacy,’ wherein present land management is molded by former land use. Agriculture in dry lands thus sequesters material in soils, and—as we also found higher material contents in residential soils than in contemporary agrarian soils—residential land use simply adds to the agrarian legacy these soils already bear. Intense human use of arid lands may cause increases in material pools in soils, a condition with potential global consequence.

© 2014, The Author(s). Mathematical epidemiology, one of the oldest and richest areas in mathematical biology, has significantly enhanced our understanding of how pathogens emerge, evolve, and spread. Classical epidemiological models, the standard for predicting and managing the spread of infectious disease, assume that contacts between susceptible and infectious individuals depend on their relative frequency in the population. The behavioral factors that underpin contact rates are not generally addressed. There is, however, an emerging a class of models that addresses the feedbacks between infectious disease dynamics and the behavioral decisions driving host contact. Referred to as “economic epidemiology” or “epidemiological economics,” the approach explores the determinants of decisions about the number and type of contacts made by individuals, using insights and methods from economics. We show how the approach has the potential both to improve predictions of the course of infectious disease, and to support development of novel approaches to infectious disease management.

The Intergovernmental Panel on Climate Change (IPCC) has suggested that large-scale use of carbon-neutral or low-carbon biomass-derived energy will be essential in order to limit carbon emissions from the world’s energy sector in the future. The IPCC envisions as much as 400 million ha being devoted to biomass energy plantations by 2050. To realize production of biomass energy at such levels — in a manner that would be both biogeophysically sustainable and socially beneficial — will require planning and policy development at sub-national levels, taking into account biogeophysical, social, cultural, economic, institutional, and other factors. This paper presents a method for spatially explicit calculations for estimating potential biomass yields over relatively large geographic regions. The calculations use geo-referenced data inputs that include rainfall, insolation, temperature, soil quality, and soil depth. The methodology is applied to the Northeast region of Brazil, which accounts for 10% of the area of South America. Northeast Brazil is an interesting site for illustrative purposes in part because it is biologically, geologically, and socio-economically diverse and in part because the main electric utility serving the region is exploring the development of biomass-based electricity generation to meet future increases in electricity demand. Results from a spatially explicit, biogeophysical model like that presented here could be combined with other spatially explicit information such as road layouts, existing land uses, population densities and growth rates, distributions of endangered species, archeologically significant areas, etc. to inform planning and policy development related to biomass energy at a regional or national level. One illustration of such an analysis is included here. For on-the-ground implementation of biomass production systems, finer-resolution analysis and intimate local participation is essential.

Microorganisms decompose organic matter and transform mineral nutrients in aquatic and terrestrial ecosystems. Despite the centrality of microbes, scientists often study ecosystem functioning without explicit reference to the microbial populations carrying out soil processes. The potential for rapid microbial growth, and the high degree of diversity and genetic exchange in microbial systems, has led to the often-held assumption that microbial catalysts do not limit the processes involved in ecosystem nutrient transfer and transformation (Meyer 1993). The utility of first-order kinetics in predicting process rates appears to confirm this assumption (Andren, Brussaard, and Clarholme 1999). Recent advances in the techniques available to study microbial communities have, however, led to a growing realization that microbial community composition can play a critical role in ecosystem functioning (Schimel 1995; Schimel and Gulledge 1998; Cavigelli and Robertson 2000). First-order kinetic models may work well at equilibrium, but their utility in capturing process rates may be compromised as systems stray from equilibrium. In order to predict the transient response of changing ecosystems, and ultimately the process rates under new equilibrium conditions, we may need to

Species are disappearing at unprecedented rates because of habitat destruc- tion. Lack of detailed knowledge about total numbers of species and their global or regional distributions, however, makes it difficult to quantify extinction rates precisely. Current estimates of extinction rates attributed to habitat destruction generally rely on species-area relationships. Many of the predictions based on species-area relationships, however, appear to overestimate the extent of current species extinction. In a previous paper, we used the species-area relationship as our starting point to derive a relationship for the areal distri- bution of endemics within a habitat, or an "endemics-area relationship." The endemics- area relationship is logically and mathematically consistent with the species-area relation- ship, but it provides additional information about the distribution of species within a biome. In this paper, we use the endemics-area relationship to improve estimates of species ex- tinction rates attributed to habitat destruction or conversion. At low levels of habitat de- struction, estimates of species loss using the endemics-area relationship are significantly lower than existing estimates, but a rapid rise in predicted species loss when a threshold of habitat loss is exceeded suggests that extrapolation of recent rates of species loss may underestimate future species extinctions under continued land clearing.

This study tested an hypothesis concerning patterns in species abundance in ecological communities. Why do the majority of species occur in low abundance, with just a few making up the bulk of the biomass? We propose that many of the minor species are analogues of the dominants in terms of the ecosystem functions they perform, but differ in terms of their capabilities to respond to environmental stresses and disturbance. They thereby confer resilience on the community with respect to ecosystem function. Under changing conditions, ecosystem function is maintained when dominants decline or are lost because functionally equivalent minor species are able to substitute for them. We have tested this hypothesis with respect to ecosystem functions relating to global change. In particular, we identified five plant functional attributes— height, biomass, specific leaf area, longevity, and leaf litter quality—that determine carbon and water fluxes. We assigned values for these functional attributes to each of the graminoid species in a lightly grazed site and in a heavily grazed site in an Australian rangeland. Our resilience proposition was cast in the form of three specific hypotheses in relation to expected similarities and dissimilarities between dominant and minor species, within and between sites. Functional similarity—or ecological distance—was determined as the euclidean distance between species in functional attribute space. The analyses provide evidence in support of the resilience hypothesis. Specifically, within the lightly grazed community, dominant species were functionally more dissimilar to one another, and functionally similar species more widely separated in abundance rank, than would be expected on the basis of average ecological distances in the community. Between communities, depending on the test used, two of three, or three of four minor species in the lightly grazed community that were predicted to increase in the heavily grazed community did in fact do so. Although there has been emphasis on the importance of functional diversity in supporting the flow of ecosystem goods and services, the evidence from this study indicates that functional similarity (between dominant and minor species, and among minor species) may be equally important in ensuring persistence (resilience) of ecosystem function under changing environmental conditions.

In this paper we develop a framework for analyzing carbon dioxide (CO 2 ) emissions trajectories from the energy and industrial sectors of the world’s nations under various policy options. A robust conclusion of our analysis is that early action by both developed and developing nations will be required to hold atmospheric CO 2 at or below doubled pre-industrial levels, and incentives for renewed investments in energy-sector technologies are a required component of early action. We therefore develop and examine an international emissions regime that: (a) in the short-term ‘jump starts’ the political and project-implementation process by providing incentives to exploit profitable or low-cost carbon reduction opportunities; (b) in the near-and medium-term addresses the inequities resulting from historic imbalances in greenhouse-gas emissions while promoting efficient pathways for carbon reduction; and (c) in the long-term recognizes the equal rights of individuals to exploit the services of the atmosphere and pursue a reasonable standard of living in a low-carbon economy. We present and analyze a proposal to promote near-term activity in carbon reduction and energy innovation through a revitalized program of international joint implementation (JI) projects for carbon emissions reduction or carbon sequestration projects. Under our proposal, JI partner nations both receive full credit for carbon reductions that can be‘banked’ and applied at a later date toward national emissions quotas in the climate convention. A finite program lifetime provides further impetus for early action. This ‘double counting’ of credits results in only modest additional cumulative carbon emissions relative to a similar scenario without cooperative partnerships. This ‘JI banking’ plan promotescritically needed scientific and institutional experience and innovation, initiates cost-efctive carbon reductions, and provides vital national flexibility in meeting eventual tarts.

Summary Evolution of a microbial nitrogen-uptake strategy that removes nitrogen at less than the maximum potential rate creates soil environments favourable for increased plant access to nitrogen. Plant productivity is thus increased, and achievement of maximum microbial biomass is facilitated through increased microbial access to plant-derived carbon. Simulations show that micro-organisms exhibiting such a ‘strategic’ nitrogen uptake will be competitively excluded by more voracious micro-organisms in a homogeneous system, but can persist in a spatially explicit system. This persistence of less voracious micro-organisms contrasts with the frequently held view that micro-organisms in soil systems take up nitrogen at the maximum possible rate. The selection of strategic or voracious microbial types in a spatially explicit environment is sensitive to the frequency of plant and microbial disturbance, and to the rate of diffusion of inorganic nitrogen in the soil system. In particular, the strategic (less voracious) microbial types are favoured under conditions of low plant disturbance, low to moderate diffusion of inorganic nitrogen, and moderate microbial disturbance. When selection favours strategic microbial types, plant access to nitrogen is increased. Plants may also evolve strategies in a spatially explicit environment that will increase population densities of favourable, strategic microbial types.

Ecologicalsystemsarecomplexassemblagesofinter-acting organisms embedded in an abiotic environ-ment.Complexityarisesfrominterspecificandintra-specific interactions among individuals or agents,interactions across trophic levels, and the interac-tions of organisms with the abiotic environmentover space and time. In addition, interactions canrange from strong and direct to weak and diffuseand are modified by both positive and negativefeedback with the environment. In our effort tounderstand pattern formation at the community orecosystem level, we are confronted with the daunt-ing array of processes that function across differentspatial and temporal scales. We are thus forced toaddress the question of how these different levels oforganization can be integrated, or how mechanismsand patterns at one level of organization can beunderstood in terms of processes operating at adifferent level of organization.The goal of this

We used overhead infrared radiators to add a constant increment of -15 W/m2, over 2 yr, to the downward heat flux on five 30-M2 montane meadow plots in Gunnison County, Colorado, USA. Heating advanced snowmelt by -1 wk, increased summer soil temperatures by up to 3?C, and reduced summer soil moisture levels by up to 25% compared to control plots. Soil microclimate response to heating varied with season, time of day, weather conditions, and location along the microclimate and vegetation gradient within each plot, with the largest temperature increase observed in daytime and in the drier, more sparsely vegetated zone of each plot. Day-to-day variation in the daily-averaged temperature response to heating in the drier zone was negatively correlated with that in the wetter zone. Our experimental manipulation provides a novel and effective method for investigating feedback processes linking climate, soil, and vegetation.

The most unique feature of Earth is the existence of life, and the most extraordinary feature of life is its diversity. Approximately 9 million types of plants, animals, protists and fungi inhabit the Earth. So, too, do 7 billion people. Two decades ago, at the first Earth Summit, the vast majority of the world's nations declared that human actions were dismantling the Earth's ecosystems, eliminating genes, species and biological traits at an alarming rate. This observation led to the question of how such loss of biological diversity will alter the functioning of ecosystems and their ability to provide society with the goods and services needed to prosper.

The value of "diversity" in social and ecological systems is frequently asserted in academic and policy literature. Diversity is thought to enhance the resilience of social-ecological systems to varied and potentially uncertain future conditions. Yet there are trade-offs; diversity in ecological and social domains has costs as well as benefits. In this paper, we examine social diversity, specifically its costs and benefits in terms of decision making in middle range or tribal societies, using archaeological evidence spanning seven centuries from four regions of the U.S. Southwest. In these nonstate societies, social diversity may detract from the capacity for collective action. We ask whether as population density increases, making collective action increasingly difficult, social diversity declines. Further, we trace the cases of low diversity and high population density across our long-temporal sequences to see how they associate with the most dramatic transformations. This latter analysis is inspired by the claim in resilience literature that reduction of diversity may contribute to reduction in resilience to varied conditions. Using archaeological data, we examine social diversity and conformity through the material culture (pottery styles) of past societies. Our research contributes to an enhanced understanding of how population density may limit social diversity and suggests the role that this association may play in some contexts of dramatic social transformation.

The risk posed by an introduced species depends on a number of factors, some of which are within the control of regulatory authorities and some of which are not. It is a product of the probability that imports will introduce new species and the expected damage done by those species. Among the risk factors taken as exogenous by the regulatory authorities are the invasiveness of the species itself (whether it is a generalist or a specialist, its plasticity, and so on), the bioclimatic similarity between the trading partners, the volume and composition of trade, and the vulnerability of the host (economic and ecological) system. The sanitary and phytosanitary (SPS) measures taken by the exporter may or may not be taken as exogenous. These together determine both the likelihood that a unit of trade will introduce species of different types and the expected damage if a particular species (or class of species) is introduced. This chapter focuses on the nature of the SPS response to the invasive species risks of international trade, and the effect this has on the dispersion of species. More particularly, it asks what determines current country-level decisions to mitigate the risks of species introductions or to adapt to the consequences of establishment and spread, and how these are reflected in the dispersion data.

This chapter considers how economists model biodiversity in coupled social ecological systems, taking two polar cases along with a more general problem. Economists assume that all human decisions are purposive: people are assumed to optimize some objective function subject to some set of initial conditions, to some set of resource constraints, and to the dynamics of the system being used. The chapter considers two polar cases and one intermediate case. One polar case involves the preservation of wilderness areas or protected parks in 'close to natural' states. A second involves the exploitation of ecosystems to produce foods, fuels and fibers. The intermediate case involves the management of ecosystems to achieve a balance between non-consumptive cultural services with consumptive provisioning services. While the constrained optimization technique applied in all three cases may be unfamiliar, the chapter tries to give the intuition behind it. It also provides a verbal description of each of the three model structures developed. In all cases the social and biogeophysical components of the coupled system are interdependent — connected through a series of feedback loops. Economists refer to such systems as 'general equilibrium systems'. That is, the dynamics of the system in some state are driven by a tendency towards the equilibrium corresponding to that state, and any perturbation has the potential to stimulate responses across the system.

By examining the consequences of simultaneous mutualism and competition between plants and decomposers, we show that testable predictions about nutrient allocation in ecosystems follow from the assumption that decomposers allocate for their own growth the fraction of mineralized nutrient that maximizes their population biomass, leaving the remainder available for plant uptake. Available data for a wide variety of ecosystems are nearly all consistent with the predicted quantitative relationships among nitrogen flow rates and nitrogen fractions in plants, decomposers, and nonliving organic matter. Our predictions are robust against changes in the detailed structure of the nutrient-cycle models we use for our derivations.

If the fraction of species in area A that are also found in one-half of that area is independent of A , the distribution of species is self-similar and a number of observed patterns in ecology, including the widely cited species-area relationship connecting species richness to censused area, follow. Self-similarity also leads to a species-abundance distribution, which deviates considerably from the commonly assumed lognormal distribution and predicts considerably more rare species than the latter. Because the abundance distribution is derived under the condition of self-similarity, it may be widely applicable beyond ecology.

"Resilience theory" is a systematic methodology for understanding the dynamics of coupled social-ecological systems (SESs). Its ongoing development requires that resilience theory be confronted with case studies to assess its capacity to help understand and develop policy for SESs. This paper synthesizes the findings from several papers in the special feature "Exploring Resilience in Social-Ecological Systems" that do just this. It then highlights key challenges facing resilience as a theory for understanding SESs and provides some avenues for future research.

The U.S. National Assessment of the Potential Consequences of Climate Variability and Change was a federally coordinated nationwide effort that involved thousands of experts and stakeholders. To draw lessons from this effort, the 10 authors of this paper, half of whom were not involved in the Assessment, developed and administered an extensive survey, prepared a series of working papers, and conducted an invitational workshop in Washington, DC, on April 29, 2004. Considering all these sources, the authors conclude that the Assessment was largely successful in implementing its basic design of distributed stakeholder involvement and in achieving its basic objectives. Future assessments could be significantly improved if greater attention were devoted to developing a collective understanding of objectives, preparing guidance materials and providing training for assessment participants, developing a budgeting mechanism which would allow greater freedom in allocating resources across various assessment activities, and creating an environment in which assessments were part of an ongoing process.

"We present evidence that there can be substantial variation in species richness in residential areas differing in their socioeconomic and cultural characteristics. Many analyses of the impacts of urbanization on biodiversity rely on traditional 'urban-to-rural' gradient measures, such as distance from urban center or population density, and thus can fail to account for the ways in which human socioeconomic and cultural characteristics are shaping the human-environment interaction and ecological outcomes. This influence of residential values and economic resources on biodiversity within the urban matrix has implications for human quality of life, for urban conservation strategies, and for urban planning."

The concept of resilience has evolved considerably since Holling's (1973) seminal paper. Different interpretations of what is meant by resilience, however, cause confusion. Resilience of a system needs to be considered in terms of the attributes that govern the system's dynamics. Three related attributes of social-ecological systems (SESs) determine their future trajectories: resilience, adaptability, and transformability. Resilience (the capacity of a system to absorb disturbance and reorganize while undergoing change so as to still retain essentially the same function, structure, identity, and feedbacks) has four components - latitude, resistance, precariousness, and panarchy - most readily portrayed using the metaphor of a stability landscape. Adaptability is the capacity of actors in the system to influence resilience (in a SES, essentially to manage it). There are four general ways in which this can be done, corresponding to the four aspects of resilience. Transformability is the capacity to create a fundamentally new system when ecological, economic, or social structures make the existing system untenable. The implications of this interpretation of SES dynamics for sustainability science include changing the focus from seeking optimal states and the determinants of maximum sustainable yield (the MSY paradigm), to resilience analysis, adaptive resource management, and adaptive governance.

Spatial variation in plant diversity has been attributed to heterogeneity in resource availability for many ecosystems. However, urbanization has resulted in entire landscapes that are now occupied by plant communities wholly created by humans, in which diversity may reflect social, economic, and cultural influences in addition to those recognized by traditional ecological theory. Here we use data from a probability-based survey to explore the variation in plant diversity across a large metropolitan area using spatial statistical analyses that incorporate biotic, abiotic, and human variables. Our prediction for the city was that land use, along with distance from urban center, would replace the dominantly geomorphic controls on spatial variation in plant diversity in the surrounding undeveloped Sonoran desert. However, in addition to elevation and current and former land use, family income and housing age best explained the observed variation in plant diversity across the city. We conclude that a functional relationship, which we term the “luxury effect,” may link human resource abundance (wealth) and plant diversity in urban ecosystems. This connection may be influenced by education, institutional control, and culture, and merits further study.

"Resilience theory is an expanding body of ideas that attempts to provide explanations for the source and role of change in adaptive systems, particularly the kinds of change that are transforming. Scholars from various disciplines have contributed to the current state of this formulation. This article proposes that resilience theory would benefit from an increasing collaboration with archaeologists, who would provide a long-term perspective on adaptive cycles. Although archaeologists and anthropologists have written provocatively about studying the resilience of past and present societies, such an approach has not become common in these disciplines. We suggest, however, that a resilience framework offers a potential mechanism for reinvigorating the conceptual base of archaeological and anthropological disciplines. To make this case, we (1) highlight three features of resilience theory, including cross-scale interactions, information flow, and phases of the adaptive cycle; (2) examine the extent to which purely natural or social science analyses would give complementary or contradictory conclusions; and (3) discuss the implications of using a long-term integrative perspective for understanding linked social and ecological systems."

Soils regulate air and water quality by storing large pools of carbon (C) and nitrogen (N). Land management decisions have an enduring influence on the integrity and size of these pools, particularly in the upper soil layers. An important challenge, therefore, is to identify how soil C and N bear the marks of both past and present land use. Several studies have documented that effects of agriculture on soil properties can persist long after agricultural abandonment, but these studies typically examine sites returning to forest or grassland. Fewer have investigated legacies of agricultural land use when formerly agrarian land becomes urban. Urban soil management may be intensive, characterized by modifications in microtopography, vegetation, and nutrient and water inputs. We thus hypothesized that urban residential land use would negate any agrarian signatures in the pool sizes of labile (readily mineralized) soil organic C and N, but that agrarian legacies would persist in pools of stable (not readily mineralized) C and N. We tested this hypothesis in arid central Arizona (USA), where residential development in the Phoenix metropolis occurred on both agrarian and uncultivated desert lands throughout the 20th Century. We used a year-long incubation to quantify labile and stable organic C and N in soils (to 15.2 cm depth) from desert land, contemporary agrarian land, residential yards that were converted from desert, and yards converted from agrarian land use. Labile N in residential soils may have been independent of historical provenance, consistent with the hypothesis that readily-mineralized pools converge on a single signature of current (residential) land use. Labile C, stable C, and stable N showed the influence of agrarian history decades after conversion to urban residential use. These agrarian legacies in currently residential soil result from the persistence of past agrarian amendments to soil, and are not artifacts of the preferential cultivation of inherently fertile land. Current residential soil management is further amending soil C and N pools on top of the legacy pools left behind by agriculture. We calculate that the persisting influence of agrarian history on soils is similar in magnitude to contemporary urban residential effects.