Strategic basin and delta planning increases the resilience of the Mekong Delta under future uncertainty.

The climate resilience of river deltas is threatened by rising sea levels, accelerated land subsidence, and reduced sediment supply from contributing river basins. Yet, these uncertain and rapidly changing threats are rarely considered in conjunction. Here we provide an integrated assessment, on basin and delta scales, to identify key planning levers for increasing the climate resilience of the Mekong Delta. We find, first, that 23 to 90% of this unusually productive delta might fall below sea level by 2100, with the large uncertainty driven mainly by future management of groundwater pumping and associated land subsidence. Second, maintaining sediment supply from the basin is crucial under all scenarios for maintaining delta land and enhancing the climate resilience of the system. We then use a bottom-up approach to identify basin development scenarios that are compatible with maintaining sediment supply at current levels. This analysis highlights, third, that strategic placement of hydropower dams will be more important for maintaining sediment supply than either projected increases in sediment yields or improved sediment management at individual dams. Our results demonstrate 1) the need for integrated planning across basin and delta scales, 2) the role of river sediment management as a nature-based solution to increase delta resilience, and 3) global benefits from strategic basin management to maintain resilient deltas, especially under uncertain and changing conditions.

Disease ecology, health and the environment: a framework to account for ecological and socio-economic drivers in the control of neglected tropical diseases.

Reducing the burden of neglected tropical diseases (NTDs) is one of the key strategic targets advanced by the Sustainable Development Goals. Despite the unprecedented effort deployed for NTD elimination in the past decade, their control, mainly through drug administration, remains particularly challenging: persistent poverty and repeated exposure to pathogens embedded in the environment limit the efficacy of strategies focused exclusively on human treatment or medical care. Here, we present a simple modelling framework to illustrate the relative role of ecological and socio-economic drivers of environmentally transmitted parasites and pathogens. Through the analysis of system dynamics, we show that periodic drug treatments that lead to the elimination of directly transmitted diseases may fail to do so in the case of human pathogens with an environmental reservoir. Control of environmentally transmitted diseases can be more effective when human treatment is complemented with interventions targeting the environmental reservoir of the pathogen. We present mechanisms through which the environment can influence the dynamics of poverty via disease feedbacks. For illustration, we present the case studies of Buruli ulcer and schistosomiasis, two devastating waterborne NTDs for which control is particularly challenging.This article is part of the themed issue 'Conservation, biodiversity and infectious disease: scientific evidence and policy implications'.

Ecology. The value of nature and the nature of value.

Ecosystems are capital assets: When properly managed, they yield a flow of vital goods and services. Relative to other forms of capital, however, ecosystems are poorly understood, scarcely monitored, and--in many important cases--undergoing rapid degradation. The process of economic valuation could greatly improve stewardship. This potential is now being realized with innovative financial instruments and institutional arrangements.

Economic incentives for rain forest conservation across scales.

Globally, tropical deforestation releases 20 to 30% of anthropogenic greenhouse gases. Conserving forests could reduce emissions, but the cost-effectiveness of this mechanism for mitigation depends on the associated opportunity costs. We estimated these costs from local, national, and global perspectives using a case study from Madagascar. Conservation generated significant benefits over logging and agriculture locally and globally. Nationally, however, financial benefits from industrial logging were larger than conservation benefits. Such differing economic signals across scales may exacerbate tropical deforestation. The Kyoto Protocol could potentially overcome this obstacle to conservation by creating markets for protection of tropical forests to mitigate climate change.

Population diversity: its extent and extinction.

Genetically distinct populations are an important component of biodiversity. This work estimates the number of populations per area of a sample of species from literature on population differentiation and the average range area of a species from a sample of distribution maps. This yields an estimate of about 220 populations per species, or 1.1 to 6.6 billion populations globally. Assuming that population extinction is a linear function of habitat loss, approximately 1800 populations per hour (16 million annually) are being destroyed in tropical forests alone.

Nocturnality and species survival.

Surveys of butterfly and moth diversity in tropical forest fragments suggest that nocturnality confers a dispersal, and possibly a survival, advantage. The butterfly faunas of smaller fragments were depauperate; in contrast, the species richness of nocturnal moths was similar in all fragments and even in pasture. The lack of correlation between butterfly and moth species richness among fragments (r2 = 0.005) is best explained by movements of moths at night when ambient conditions in forest and pasture are most similar; butterflies face substantial daytime temperature, humidity, and solar radiation barriers. This interpretation is supported by information on birds, beetles, and bats.

Restoring Value to the World's Degraded Lands.

Roughly 43 percent of Earth's terrestrial vegetated surface has diminished capacity to supply benefits to humanity because of recent, direct impacts of land use. This represents an approximately 10 percent reduction in potential direct instrumental value (PDIV), defined as the potential to yield direct benefits such as agricultural, forestry, industrial, and medicinal products. If present trends continue, the global loss of PDIV could reach approximately 20 percent by 2020. From a biophysical perspective, recovery of approximately 5 percent of PDIV is feasible over the next 25 years. Capitalizing on natural recovery mechanisms is urgently needed to prevent further irreversible degradation and to retain the multiple values of productive land.

The fertility plateau in Costa Rica: a review of causes and remedies.

PIP: Costa Rica achieved a substantial reduction in its overall fertility rate in a very short period of time. The halving of the fertility rate which occurred in less than ten years in Costa Rica transpired over the course of 100 years in France and 170 in Sweden. The level of contraceptive use in Costa Rica is twice that in other Central American nations. The authors summarize the recent demographic history of Costa Rica and review factors influencing its remarkable fertility decline. They then discuss possible explanations for the ensuing fertility plateau and conclude by suggesting strategies for affecting a further decrease in fertility rates. With regard to the reasons for the fertility plateau, cultural factors, socioeconomic factors, declining government commitment and family planning services, education, and the Church are considered. To reduce the level of fertility even further, the authors recommend that the government adopt a clear population policy which could serve as a basis for other changes such as increased support of family planning programs, improvements in the educational system, increased women's status and employment opportunities, and extensive education in schools and through the mass media on the socioeconomic and environmental effects of overpopulation. It is important to increase Costa Ricans' understanding of the negative impacts of continued population growth and the role of individual family planning decisions in that growth.^ieng

Double keystone bird in a keystone species complex.

Species in a Colorado subalpine ecosystem show subtle interdependences. Red-naped sapsuckers play two distinct keystone roles. They excavate nest cavities in fungus-infected aspens that are required as nest sites by two species of swallows, and they drill sap wells into willows that provide abundant nourishment for themselves, hummingbirds, orange-crowned warblers, chipmunks, and an array of other sap robbers. The swallows thus depend on, and the sap robbers benefit from, a keystone species complex comprised of sapsuckers, willows, aspens, and a heartwood fungus. Disappearance of any element of the complex could cause an unanticipated unraveling of the community.

An exploratory model of the impact of rapid climate change on the world food situation.

A simple, globally aggregated, stochastic-simulation model was constructed to examine the effects of rapid climatic change on agriculture and the human population. The model calculates population size and the production, consumption and storage of grain under different climate scenarios over a 20-year projection time. In most scenarios, either an optimistic baseline annual increase of agricultural output of 1.7% or a more pessimistic appraisal of 0.9% was used. The rate of natural increase of the human population exclusive of excess hunger-related deaths was set as 1.7% per year and climatic changes with both negative and positive impacts on agriculture were assessed. Analysis of the model suggests that the number of hunger-related deaths could double (with reference to an estimated 200 million deaths in the past two decades) if grain production keeps pace with population growth but climatic conditions are unfavourable. If the rate of increase in grain production is about half that of population growth, the number of hunger-related deaths could increase about fivefold (over past levels); the impact of climatic change is relatively small under this imbalance. Even favourable climatic changes that enhance agricultural production may not prevent a fourfold increase in deaths (over past levels) under scenarios where population growth outpaces production by about 0.8% per annum. These results may foreshadow a fundamental change where, for the first time, absolute global food deficits compound inequities in food production and distribution in causing famine. The model also highlights the effectiveness of reducing population growth rates as a strategy for minimizing the impact of global climate change and maintaining food supplies for everyone.