Publications

Why wealth is systematically lower in the tropics remains a puzzle. We point out that latitude may have fundamental economic consequence because it plays a key role in how countries experience geophysical processes that have economic implications. We demonstrate that annual fluctuations in the El Nino Southern Oscillation (ENSO) leads to hotter and dryer local weather across tropical countries and subsequently to substantial losses in agricultural yields, output, and value-added. If volatility in agricultural production impedes economic growth, the relatively stronger influence of ENSO on the tropics may offer yet another partial explanation for slower historical growth in the tropics.

This paper combines panel data on monthly mortality rates of US states and daily temperature variables for over a century (1900-2004) to explore the regional evolution of the temperature-mortality relationship and documents two key findings. First, the impact of extreme heat on mortality is notably smaller in states that more frequently experience extreme heat. Second, the difference in the heat-mortality relationship between hot and cold states declined over 1900-2004, though it persisted through 2004. Continuing differences in the mortality consequences of hot days suggests that health motivated adaptation to climate change may be slow and costly around the world.

Determining how various factors contribute to the invasibility of systems is essential for both understanding community formation and informing management of natural areas. Research demonstrating that predators can provide biotic resistance to invasions by consuming invasive species has led to the presence of healthy predator populations being associated with reduced invasion potential of ecosystems. However, predators structure communities in many ways and their presence could also potentially facilitate invasions if they decrease populations of native species that compete with or consume an invader. We considered these two impacts of predators on invasion by analyzing the effects of two keystone predators (Pisaster spp. and Enhydra lutris nereis) on two foundation species (a native mussel Mytilus californianus and the invasive exotic bryozoan Watersipora subtorquata, a putative competitor for space with Mytilus californianus). Both native predators were found to facilitate the invasion of the exotic bryozoan, and the rate of invasion was highest when both predators were present. Facilitation of W. subtorquata occurred via indirect mechanisms that partly involved the removal of a competitor (mussels) via predation. These results illustrate that although predators can provide biotic resistance to invasion, healthy predator populations do not always confer this advantage and in fact may facilitate invasions. Therefore, implementation of management actions to enhance populations of top predators could also potentially increase the invasibility of some ecosystems.

Land-use change is a leading cause of environmental degradation in terrestrial systems and has important implications for natural resource use. Economists have a long tradition of studying land use and in recent decades have developed empirical land-use models using econometric and optimization approaches. Integration of these land-use and biophysical models allows for a more comprehensive analysis of the consequences of future land-use change and the use of land-use policies to avoid undesirable outcomes. I provide a conceptual framework for the modeling approach, describing the individual components of an analysis as well as how they are linked together. My review describes how the literature has evolved to take advantage of spatial data and greater computing capabilities. Although most researchers have used either an econometric or an optimization approach, there is potential to combine these methods to identify more efficient land-use policies that still meet criteria of tractability and political acceptance.

Land use change around protected areas can diminish their conservation value, making it important to predict future land use changes nearby. Our goal was to evaluate future land use changes around protected areas of different types in the United States under different socioeconomic scenarios. We analyzed econometric-based projections of future land use change to capture changes around 1260 protected areas, including National Forests, Parks, Refuges, and Wilderness Areas, from 2001 to 2051, under different land use policies and crop prices. Our results showed that urban expansion around protected areas will continue to be a major threat, and expand by 67% under business-as-usual conditions. Concomitantly, a substantial number of protected areas will lose natural vegetation in their surroundings. National land-use policies or changes in crop prices are not likely to affect the overall pattern of land use, but can have effects in certain regions. Discouraging urbanization through zoning, for example, can reduce future urban pressures around National Forests and Refuges in the East, while the implementation of an afforestation policy can increase the amount of natural vegetation around some Refuges throughout the U.S. On the other hand, increases in crop prices can increase crop/pasture cover around some protected areas, and limit the potential recovery of natural vegetation. Overall, our results highlight that future land-use change around protected areas is likely to be substantial but variable among regions and protected area types. Safeguarding the conservation value of protected areas may require serious consideration of threats and opportunities arising from future land use.

This paper presents a survey of the empirical literature studying the relationship between health outcomes, temperature, and adaptation to temperature extremes. The objectives of the paper are to highlight the many remaining gaps in the empirical literature and to provide guidelines for improving the current Integrated Assessment Model (IAM) literature that seeks to incorporate human health and adaptation in its framework. I begin by presenting the conceptual and methodological issues associated with the measurement of the effect of temperature extremes on health, and the role of adaptation in possibly muting these effects. The main conclusion that emerges from the literature is that despite the wide variety of data sets and settings most studies find that temperature extremes lead to significant reductions in health, generally measured with excess mortality. Regarding the role of adaptation in mitigating the effects of extreme temperature on health, the available knowledge is limited, in part due to the few real-world data sets on adaptation behaviors. Finally, the paper discusses the implications of the currently available evidence for assessments of potential human health impacts of global climate change.

Biological diversity is known to play an important role in generating and maintaining ecosystem productivity and other functions and has consequently become a central focus of many efforts to preserve ecosystem services. Theoretical parallels suggest the diversity of fishing fleets may have a similarly important role in determining the productivity and ecological impacts of fisheries, but this possibility has rarely been explored. Here I present theoretical analyses showing that the diversity of métiers — combinations of technology, target species, and fishing grounds — and technical efficiencies in a fishing fleet have important impacts on the productivity, profitability, and ecological impacts of fisheries, particularly mixed-stock or multispecies fisheries. Diversification of métiers can increase yields and reduce threats to weak stocks in both managed and unmanaged multispecies fisheries. Diversification of technical efficiencies creates opportunities for larger profits in managed fisheries, but often decreases yields and worsens impacts on weak stocks in unmanaged fisheries. These results suggest that the potential impact of management may be highest in fisheries with diverse fleets.

Overfishing and degradation of the marine environment continue to plague coastal communities worldwide, with multiple diverse solutions being proposed. Territorial Use Rights for Fisheries (TURFs) is a fishery management approach that aligns fishers’ incentives with sustainability, while marine reserves have proven effective for ecosystem protection, and in some cases for fishery enhancement. These two management approaches are often used in isolation, leaving the potential utility of integrating them poorly understood. We examine cases where TURFs and marine reserves have been implemented together to create “TURF-reserves”. We compiled a database of 27 TURF-reserves and collected information on the governance, management, enforcement, fishing practices, fishing rights, regulations, and design attributes for each site. We address several research questions including: what species are managed with TURF-reserves, how are TURF-reserves created and who is involved in the process? Our findings show that the majority of surveyed TURF-reserves arose from previously established TURF systems that target a range of fisheries, and multiple entities play a role in TURF-reserve development and management. We also examine the differences between two TURF-reserve archetypes and find that those developed with a strong history of customary tenure share distinct qualities from those created in a more recently established, government-mandated system.

Anthropogenic impacts are increasingly affecting the world's oceans. Networks of marine protected areas (MPAs) provide an option for increasing the ecological and economic benefits often provided by single MPAs. It is vital to empirically assess the effects of MPA networks and to prioritize the monitoring data necessary to explain those effects. We summarize the types of MPA networks based on their intended management outcomes and illustrate a framework for evaluating whether a connectivity network is providing an outcome greater than the sum of individual MPA effects. We use an analysis of an MPA network in Hawai'i to compare networked MPAs to non-networked MPAs to demonstrate results consistent with a network effect. We assert that planning processes for MPA networks should identify their intended outcomes while also employing coupled field monitoring-simulation modeling approaches, a powerful way to prioritize the most relevant monitoring data for empirically assessing MPA network performance.

Environmental certification and consumer awareness programs are designed to create market incentives for implementing fisheries and aquaculture practices that are more sustainable. Typically focused on particular species and activities, such programs have so far triggered few changes to improve seafood sustainability. Here, we present a conceptual, system-wide fisheries and aquaculture certification program designed to recognize and promote change toward more sustainable and resilient seafood production systems. In contrast to previous efforts, this program concentrates on both ecosystems and various human stakeholders, relies on an adaptive management approach (termed “continual improvement”) to enhance outcomes, and considers socioeconomic factors. The goal of this program is to support the restoration and maintenance of healthy ecosystem states and thriving human communities as well as the improvement of whole social–ecological systems.

Marine spatial planning (MSP), whereby areas of the ocean are zoned for different uses, has great potential to reduce or eliminate conflicts between competing management goals, but only if strategically applied. The recent literature overwhelmingly agrees that including stakeholders in these planning processes is critical to success; but, given the countless alternative ways even simple spatial regulations can be configured, how likely is it that a stakeholder-driven process will generate plans that deliver on the promise of MSP? Here, we use a spatially explicit, dynamic bioeconomic model to show that stakeholder-generated plans are doomed to fail in the absence of strong scientific guidance. While strategically placed spatial regulations can improve outcomes remarkably, the vast majority of possible plans fail to achieve this potential. Surprisingly, existing scientific rules of thumb do little to improve outcomes. Here, we develop an alternative approach in which models are used to identify efficient plans, which are then modified by stakeholders. Even if stakeholders alter these initial proposals considerably, results hugely outperform plans guided by scientific rules of thumb. Our results underscore the importance of spatially explicit dynamic models for the management of marine resources and illustrate how such models can be harmoniously integrated into a stakeholder-driven MSP process.

The world's oceans are governed as a system of over 150 sovereign exclusive economic zones (EEZs, ∼42% of the ocean) and one large high seas (HS) commons (∼58% of ocean) with essentially open access. Many high-valued fish species such as tuna, billfish, and shark migrate around these large oceanic regions, which as a consequence of competition across EEZs and a global race-to-fish on the HS, have been over-exploited and now return far less than their economic potential. We address this global challenge by analyzing with a spatial bioeconomic model the effects of completely closing the HS to fishing. This policy both induces cooperation among countries in the exploitation of migratory stocks and provides a refuge sufficiently large to recover and maintain these stocks at levels close to those that would maximize fisheries returns. We find that completely closing the HS to fishing would simultaneously give rise to large gains in fisheries profit (>100%), fisheries yields (>30%), and fish stock conservation (>150%). We also find that changing EEZ size may benefit some fisheries; nonetheless, a complete closure of the HS still returns larger fishery and conservation outcomes than does a HS open to fishing.

The argument persists that the continued overexploitation by many fisheries around the world is evidence that current approaches to fisheries management are failing, and that more precautionary management approaches are needed. We review the available estimates of the status of fish stocks from three sources: the FAO's “State of Marine Resources”, a database on scientific stock assessments, and recent estimates from statistical models designed to determine the status of unassessed fish stocks. The two key results are (i) that stocks that are scientifically assessed are in better shape and indeed are not typically declining but rebuilding, and (ii) that large stocks appear to be in better shape than small stocks. These results support the view that stocks that are managed are improving, while stocks that are not managed are not. Large stocks receive far more management attention than small stocks in jurisdictions that have active fisheries management systems, and most unassessed stocks are simply not managed. We assert that fisheries management as currently practised can (and often does) lead to sustainable fisheries, and what is needed is to actively manage the unassessed fisheries of the world. More precautionary management is not necessarily needed to ensure the sustainability of managed fisheries.

A recent study by Burke et al. [Burke M, Miguel E, Satyanath S, Dykema J, Lobell D (2009) Proc Natl Acad Sci USA 106(49):20670–20674] reports statistical evidence that the likelihood of civil wars in African countries was elevated in hotter years. A following study by Buhaug [Buhaug H (2010) Proc Natl Acad Sci USA 107(38):16477–16482] reports that a reexamination of the evidence overturns Burke et al.’s findings when alternative statistical models and alternative measures of conflict are used. We show that the conclusion by Buhaug is based on absent or incorrect statistical tests, both in model selection and in the comparison of results with Burke et al. When we implement the correct tests, we find there is no evidence presented in Buhaug that rejects the original results of Burke et al.

Chondrichthyans—the class of fish that includes sharks and rays—are in a bad, bad way. Their numbers have plummeted, mostly due to overfishing, which is largely driven by the demand for shark fin soup (Jackson et al., 2001; Myers and Worm, 2003). All attempts at saving species have fallen short, not because of a lack of concern, but instead because of a lack of data. It is difficult to know just how depleted sharks and rays are in number, just as it is difficult to determine how and where conservation efforts are most desperately needed. This is concerning not just for chondrichthyans, but also for entire ecosystems, because the removal of large-bodied predators, such as sharks, can cause entire food webs to collapse (Stevens et al., 2000; Mumby et al., 2006; Heithaus et al., 2008).

To address this knowledge gap, Nicholas Dulvy of Simon Fraser University and co-workers in Canada, UK, USA, Australia, New Zealand and South Africa have performed a systematic evaluation of the relative extinction risk for more than 1000 species of sharks, rays and the less well known chimaeras (Dulvy et al., 2014). Their findings—which have been published in eLife—are alarming, but more importantly, the story they reveal helps to frame the chondrichthyan problem in ways that can help guide effective solutions.

Although market-based incentives have helped resolve many environmental challenges, conservation markets still play a relatively minor role in wildlife management. Establishing property rights for environmental goods and allowing trade between resource extractors and resource conservationists may offer a path forward in conserving charismatic species like whales, wolves, turtles, and sharks. In this paper, we provide a conceptual model for implementing a conservation market for wildlife and evaluate how such a market could be applied to three case studies for whales (minke [Balaenoptera acutorostrata], bowhead [Balaena mysticetus], and gray [Eschrictius robustus]). We show that, if designed and operated properly, such a market could ensure persistence of imperiled populations, while simultaneously improving the welfare of resource harvesters.

We are glad our recent paper in Ecological Applications has stimulated new discussion on the role of conservation markets in wildlife management. In their response, Smith et al. identify four important challenges to implementing a whale conservation market. We agree that the details of market-based policies are important and highlighted several challenges in our paper in the market design for whales. But we believe the challenges highlighted by Smith et al. (and indeed by our own analysis) will be present under any institutional regime and are surmountable in a market with appropriate design. The purpose of our paper was to propose a general framework for how a market for wildlife species such as whales might perform in order to stimulate new thinking on the many complexities associated with a market-based approach. We are delighted that our paper has accomplished this so quickly, and remain enthusiastic about the exciting research ahead.

The overall concern raised by Smith et al. is that, because whales are an impure public good, any policy that fails to capture all nonmarket benefits and potential free riding will lead to a suboptimal outcome. We agree that any approach that ignores nonmarket and external benefits could lead to a suboptimal outcome. Importantly, we never claimed that a conservation market would lead to a socially optimal outcome. Rather, we proposed that it could be Pareto improving (make both sides better off) relative to the status quo. Furthermore, if conservationists purchase all of the shares (which may well occur), then indeed this solution may be socially optimal; an important (and perhaps likely) scenario that Smith et al. failed to recognize. A simple version of the market, which has been mirrored for in-stream flow water rights, is to cap the whale harvest at the current level of take (provided it is biologically safe), and to provide a platform where conservationists can compensate whalers to reduce harvest from that point. If such trade occurs, and we have strong evidence that it could, it would improve the welfare of both sides. More complicated market designs are also possible, and our simulations illustrate several cases. That said, we think the impure public good nature of whales could lead to interesting new research and insights about market design and outcomes (compared to some reasonable counterfactual) in these contexts.

Property rights are commonly touted as a solution to common pool resource problems. In practice, however, the security of property rights over natural resources varies substantially; this may affect returns to ownership and asset values. We use an analytical model to examine the effects of insecure property rights to natural resources on the market value of assets. We then use a unique dataset of fisheries from three countries to examine empirically how differences in property rights affect market outcomes. We find significant asset market capitalization of insecurity arising from (1) ownership disputes, (2) illegal extraction from resource stocks, and (3) the possibility of government revocation of rights.

Increases in the demand and price for industrial metals, combined with advances in technological capabilities have now made deep-sea mining more feasible and economically viable. In order to balance economic interests with the conservation of abyssal plain ecosystems, it is becoming increasingly important to develop a systematic approach to spatial management and zoning of the deep sea. Here, we describe an expert-driven systematic conservation planning process applied to inform science-based recommendations to the International Seabed Authority for a system of deep-sea marine protected areas (MPAs) to safeguard biodiversity and ecosystem function in an abyssal Pacific region targeted for nodule mining (e.g. the Clarion–Clipperton fracture zone, CCZ). Our use of geospatial analysis and expert opinion in forming the recommendations allowed us to stratify the proposed network by biophysical gradients, maximize the number of biologically unique seamounts within each subregion, and minimize socioeconomic impacts. The resulting proposal for an MPA network (nine replicate 400 × 400 km MPAs) covers 24% (1 440 000 km²) of the total CCZ planning region and serves as example of swift and pre-emptive conservation planning across an unprecedented area in the deep sea. As pressure from resource extraction increases in the future, the scientific guiding principles outlined in this research can serve as a basis for collaborative international approaches to ocean management.

Widespread concern over global fish stocks has prompted an increase in research and initiatives aimed at rebuilding ailing fisheries and incentivizing sustainable fishing practices. This promising focus on solutions coincides with a burgeoning consumer and retailer demand for environmentally friendly products (Figure 1). Sustainability certification, labeling, and consumer guides (e.g., Marine Stewardship Council, Fair Trade, Seafood Watch, etc.) are signals that help eco-minded consumers identify products that meet their standards. Accurate signals offer an immense opportunity to incentivize sustainability, increasing demand and profits for sustainable producers. Yet, while the growing number of seafood certification programs and consumer seafood guides fuel and inform demand, the pace of change is slow. One key barrier to progress is the significant lag between the implementation of reforms and the recovery of fish stocks. Without preemptive credits within certification protocols for conservation actions that can be expected to benefit the stock over time, the incentives for reforms may be limited.

Many potential conservation reforms could qualify for preemptive credit, but the most conspicuous absence is the lack of credit for marine protected areas (MPAs). Marine protected areas are one of the most important tools for conserving the ocean's ecosystems. MPAs, similar to protected areas on land, are locations where regulations prohibit specific human activities. There has been considerable research about the effects of MPAs, particularly focused on a common class of MPAs in which all fishing is prohibited (no-take marine reserves). Studies from more than 120 no-take marine reserves around the world consistently reveal the conservation benefits of this type of protection, including higher total biomass, abundance, and average size of fish within reserves [1] (Figure 2). The data from these many existing MPAs, combined with improving spatial fisheries models, allow us to predict an MPA's future conservation benefits long before they are realized. Such empirically based model forecasts could be used to assign preemptive credit for MPAs within certification frameworks when the MPA is implemented. Doing so would reward existing MPAs for their contributions to sustainable fisheries and would provide more powerful short-term incentives to create well-designed new MPAs.