Showing papers by "International Institute for Applied Systems Analysis published in 2005"

Evolution of indirect reciprocity.

Abstract: Natural selection is conventionally assumed to favour the strong and selfish who maximize their own resources at the expense of others. But many biological systems, and especially human societies, are organized around altruistic, cooperative interactions. How can natural selection promote unselfish behaviour? Various mechanisms have been proposed, and a rich analysis of indirect reciprocity has recently emerged: I help you and somebody else helps me. The evolution of cooperation by indirect reciprocity leads to reputation building, morality judgement and complex social interactions with ever-increasing cognitive demands.

Socio-economic and climate change impacts on agriculture: an integrated assessment, 1990–2080

Abstract: A comprehensive assessment of the impacts of climate change on agro-ecosystems over this century is developed, up to 2080 and at a global level, albeit with significant regional detail. To this end an integrated ecological–economic modelling framework is employed, encompassing climate scenarios, agro-ecological zoning information, socio-economic drivers, as well as world food trade dynamics. Specifically, global simulations are performed using the FAO/IIASA agro-ecological zone model, in conjunction with IIASAs global food system model, using climate variables from five different general circulation models, under four different socio-economic scenarios from the intergovernmental panel on climate change. First, impacts of different scenarios of climate change on bio-physical soil and crop growth determinants of yield are evaluated on a 5′×5′ latitude/longitude global grid; second, the extent of potential agricultural land and related potential crop production is computed. The detailed bio-physical results are then fed into an economic analysis, to assess how climate impacts may interact with alternative development pathways, and key trends expected over this century for food demand and production, and trade, as well as key composite indices such as risk of hunger and malnutrition, are computed. This modelling approach connects the relevant bio-physical and socio-economic variables within a unified and coherent framework to produce a global assessment of food production and security under climate change. The results from the study suggest that critical impact asymmetries due to both climate and socio-economic structures may deepen current production and consumption gaps between developed and developing world; it is suggested that adaptation of agricultural techniques will be central to limit potential damages under climate change.

Average remaining lifetimes can increase as human populations age

Abstract: Increases in median ages, the most commonly used measure of population ageing, are rapid in today's wealthier countries, and population ageing is widely considered to be a significant challenge to the well-being of citizens there. Conventional measures of age count years since birth; however, as lives lengthen, we need to think of age also in terms of years left until death or in proportion to the expanding lifespan. Here we propose a new measure of ageing: the median age of the population standardized for expected remaining years of life. We show, using historical data and forecasts for Germany, Japan and the United States, that although these populations will be growing older, as measured by their median ages, they will probably experience periods in which they grow younger, as measured by their standardized median ages. Furthermore, we provide forecasts for these countries of the old-age dependency ratio rescaled for increases in life expectancy at birth. These ratios are forecasted to change much less than their unscaled counterparts, and also exhibit periods when the population is effectively growing younger.

Soil Atlas of Europe

Abstract: Soil maps of Europe, published by the EU and the European Soil Bureau Network; with varying scales 1:1.500.000 1:1.750.000 1:2.000.000 1:2.200.000 1:2.500.000 1:3.000.000 1:6.500.000

Refocusing Disaster Aid

Abstract: With new modeling techniques for estimating and pricing the risks of natural disasters, the donor community is now in a position to help the poor cope with the economic repercussions of disasters by assisting before they happen Such assistance is possible with the advent of novel insurance instruments for transferring catastrophe risks to the global financial markets Donor-supported risk-transfer programs not only would leverage limited disaster-aid budgets but also would free recipient countries from depending on the vagaries of postdisaster assistance Both donors and recipients stand to gain, especially because the instruments can be closely coupled with preventive measures

Policies addressing the tempo effect in low-fertility countries

Abstract: The possible negative consequences of current low fertility levels are causing increasing concern, particularly in countries where the total fertility rate is below 1.5. Social inertia and self-reinforcing processes may make it difficult to return to higher levels once fertility has been very low for some time, creating a possible "low-fertility trap." Policies explicitly addressing the fertility-depressing effect of increases in the mean age at childbearing (the tempo effect) may be a way to raise period fertility to somewhat higher levels and help escape the "low-fertility trap" before it closes. Reforms in the school system may affect the timing of childbearing by lowering the age at completion of education. A more efficient school system, which provides the same qualifications with a younger school-leaving age, is potentially capable of increasing period fertility and hence exerting a rejuvenating effect on the age composition, even if the levels of cohort fertility remain unchanged. Such policies may also have a positive effect on completed cohort fertility.

Adaptive evolution of social traits: Origin, trajectories, and correlations of altruism and mobility

Abstract: Social behavior involves “staying and helping,” two individual attributes that vary considerably among organisms. Investigating the ultimate causes of such variation, this study integrates previously separate lines of research by analyzing the joint evolution of altruism and mobility. We unfold the network of selective pressures and derive how these depend on physiological costs, eco‐evolutionary feedbacks, and a complex interaction between the evolving traits. Our analysis highlights habitat saturation, both around individuals (local aggregation) and around unoccupied space (local contention), as the key mediator of altruism and mobility evolution. Once altruism and mobility are allowed to evolve jointly, three general insights emerge. First, the cost of mobility affects the origin of altruism, determining whether and how quickly selfishness is overcome. Second, the cost of altruism determines which of two qualitatively different routes to sociality are taken: an evolutionary reduction of mobil...

Acclimation of Russian forests to recent changes in climate

Abstract: Assessments made over the past few decades have suggested that boreal forests may act as a sink for atmospheric carbon dioxide. However, the fate of the newly accumulated carbon in the living forest biomass is not well understood, and the estimates of carbon sinks vary greatly from one assessment to another. Analysis of remote sensing data has indicated that the carbon sinks in the Russian forests are larger than what has been estimated from forest inventories. In this study, we show that over the past four decades, the allometric relationships among various plant parts have changed in the Russian forests. To this end, we employ two approaches: (1) analysis of the database, which contains 3196 sample plots; and (2) application of developed models to forest inventory data. Within the forests as a whole, when assessed at the continental scale, we detect a pronounced increase in the share of green parts (leaves and needles). However, there is a large geographical variation. The shift has been largest within the European Russia, where summer temperatures and precipitation have increased. In the Northern Taiga of Siberia, where the climate has become warmer but drier, the fraction of the green parts has decreased while the fractions of aboveground wood and roots have increased. These changes are consistent with experiments and mathematical models that predict a shift of carbon allocation to transpiring foliage with increasing temperature and lower allocation with increasing soil drought. In light of this, our results are a possible demonstration of the acclimation of trees to ongoing warming and changes in the surface water balance. Independent of the nature of the observed changes in allometric ratios, the increase in the share of green parts may have caused a misinterpretation of the satellite data and a systematic overestimation by remote sensing methods of the carbon sink for living biomass of the Russian forest.

Understanding mutualism when there is adaptation to the partner

Abstract: Summary 1 A mutualism is a mutually beneficial interaction between individuals of two species. Here we show that the degree of benefit resulting from an interaction depends on whether adaptation within the mutualism is considered. 2 A species’ proximate response measures the short-term effect of addition or removal of the partner species, without allowing for any adaptation. We define a proximate mutualism as an interaction in which removal of each partner results in a decreased performance of the other, i.e. both species show a positive proximate response to the presence of the partner. 3 A proximate mutualism might, however, only reflect evolved dependence (i.e. the species has lost its ability to perform well without the partner). Some authors therefore insist on an ultimate criterion, regardless of the use of proximate responses in almost all empirical studies. 4 A species’ ultimate response measures the long-term effect of adding or removing the partner species, thus allowing the focal species to adapt. In an ultimate mutualism neither partner could ever have performed as well without the other. In other words, a mutualism is called ultimate if both species show a positive ultimate response to the presence of the partner. Despite the conceptual attractiveness of this definition, ultimate responses are difficult to measure, rendering its use operationally problematic. 5 Mutualistic evolution , the evolution of a trait that is costly to the bearer but beneficial to its partner, is not, paradoxically, a necessary consequence of either proximate or ultimate mutualism. Another counterintuitive result is that even obligate mutualisms are not necessarily ultimate interactions. 6 We conclude that the proximate response is the only workable criterion for mutualism. Our understanding of mutualism, however, requires further evaluation of how evolved dependence may be responsible for such responses. 7 These concepts clarify the ongoing debate about whether plant‐herbivore interactions can be considered as mutualistic. 8 This is not a semantic case of hair splitting: naive aspects in current views of mutualism need revision. In most, if not all, interactions now considered as mutualisms, some of the measured benefits are likely to result from evolved dependence, rather than what we would like to consider as ultimate benefits.

Link between population dynamics and dynamics of Darwinian evolution

Abstract: We provide the link between population dynamics and the dynamics of Darwinian evolution via studying the joint population dynamics of similar populations. Similarity implies that the relative dynamics of the populations is slow compared to, and decoupled from, their aggregated dynamics. The relative dynamics is simple, and captured by a Taylor expansion in the difference between the populations. The emerging evolution is directional, except at the singular points of the evolutionary state space. Here ‘‘evolutionary branching’’ may occur. The diversification of life forms thus is demonstrated to be a natural consequence of the Darwinian process.

Priorities in Global Assistance for Health, AIDS, and Population

Abstract: This article makes three points regarding international assistance in health, AIDS, and population. First, despite growing attention in the development policy dialogue, the share of health (broadly considered) in total assistance is actually declining, not increasing, if assistance for the HIV/AIDS crisis is taken out of the picture. Second, interventions financed by international health assistance do not closely correspond to the burden of disease as conventionally calculated. HIV/AIDS receives a share of assistance in excess of its contribution to the global burden of disease, and reasons for this are adduced. Third, despite the emphasis on aligning international assistance to country priorities, a comparison of how health is treated in poverty-reduction strategies and the nature of health assistance reveals no clear relationship between the two. This suggests that there may be room for improvement in the process of preparing such strategies, the allocation of health assistance, or both.

What we have also learned: adaptive speciation is theoretically plausible

Abstract: A recent Perspectives article by Gavrilets (2003) on the theory of speciation ignored advances in understanding processes of adaptive speciation, in which the splitting of lineages is an adaptation caused by frequency-dependent selection. Adaptive, or sympatric, speciation has been modeled since the 1960s, but the large amount of attention from both empirical and theoretical biologists that adaptive speciation has received in recent years goes far beyond what was described in Gavrilets' paper. Due to conceptual advances based on the theory of adaptive dynamics, adaptive speciation has emerged as a theoretically plausible evolutionary process that can occur in many different ecological settings.

Impact of the Arctic Oscillation pattern on interannual forest fire variability in Central Siberia

Abstract: [1] Russia's forests play an important role in the global carbon cycle. Because of their scale and interannual variability, forest fires can change the direction of the net carbon flux over Eurasia. 2002 and 2003 were the first two consecutive years in the atmospheric record in which the carbon content rose by more than 2 ppm per year. Northern Hemisphere fires could be the reason. We show that 2002 and 2003 were the two years with the largest fire extent in Central Siberia since 1996 using new measurements of burned forest area in Central Siberia derived from remote sensing. To quantify the relationship between Siberian forest fires and climate variability, we compare these measurements with time-series of large-scale climatic indices for the period 1992–2003. This paper is amongst the first studies that analyse statistical relationships between interannual variability of forest fires in Russia and climate indices. Significant relationships of annual burned forest area with the Arctic Oscillation, summer temperatures, precipitation, and the El Nino index NINO4 were found (p 0.1). Interannual forest fire variability in Central Siberia could best be explained by a combination of the Arctic Oscillation index and regional summer temperatures (r2 = 0.80).

Testing Sustainability of German Fiscal Policy. Evidence for the Period 1960-2003

Abstract: In this paper, we test whether German public debt has been sustainable by resorting to a test proposed by Bohn (1998). We apply non-parametric and semi-parametric regressions with time depending coefficients. This test shows that the mean of the coefficient relevant for sustainability has been significantly positive over the time period considered. However, there is a negative trend in that coefficient which seems to have ceased to decline only in the middle to late 1990s. Further, we find evidence that the response of the primary deficit is a U-shaped function of the debt ratio which first declines and then rises after a certain threshold of the debt ratio is exceeded.

Speciation: more likely through a genetic or through a learned habitat preference?

Abstract: A problem in understanding sympatric speciation is establishing how reproductive isolation can arise when there is disruptive selection on an ecological trait. One of the solutions that has been proposed is that a habitat preference evolves, and that mates are chosen within the preferred habitat. We present a model where the habitat preference can evolve either by means of a genetic mechanism or by means of learning. Employing an adaptive-dynamical analysis, we show that evolution proceeds either to a single population of specialists with a genetic preference for their optimal habitat, or to a population of generalists without a habitat preference. The generalist population subsequently experiences disruptive selection. Learning promotes speciation because it increases the intensity of disruptive selection. An individual-based version of the model shows that, when loci are completely unlinked and learning confers little cost, the presence of disruptive selection most probably leads to speciation via the simultaneous evolution of a learned habitat preference. For high costs of learning, speciation is most likely to occur via the evolution of a genetic habitat preference. However, the latter only happens when the effect of mutations is large, or when there is linkage between genes coding for the different traits.

On state-space reduction in multi-strain pathogen models, with an application to antigenic drift in influenza A.

Abstract: Many pathogens exist in phenotypically distinct strains that interact with each other through competition for hosts. General models that describe such multi-strain systems are extremely difficult to analyze because their state spaces are enormously large. Reduced models have been proposed, but so far all of them necessarily allow for coinfections and require that immunity be mediated solely by reduced infectivity, a potentially problematic assumption. Here, we suggest a new state-space reduction approach that allows immunity to be mediated by either reduced infectivity or reduced susceptibility and that can naturally be used for models with or without coinfections. Our approach utilizes the general framework of status-based models. The cornerstone of our method is the introduction of immunity variables, which describe multi-strain systems more naturally than the traditional tracking of susceptible and infected hosts. Models expressed in this way can be approximated in a natural way by a truncation method that is akin to moment closure, allowing us to sharply reduce the size of the state space, and thus to consider models with many strains in a tractable manner. Applying our method to the phenomenon of antigenic drift in influenza A, we propose a potentially general mechanism that could constrain viral evolution to a one-dimensional manifold in a two-dimensional trait space. Our framework broadens the class of multi-strain systems that can be adequately described by reduced models. It permits computational, and even analytical, investigation and thus serves as a useful tool for understanding the evolution and ecology of multi-strain pathogens.

Evolution of specialization and ecological character displacement of herbivores along a gradient of plant quality

Abstract: We study the combined evolutionary dynamics of herbivore specialization and ecological character displacement, taking into account foraging behavior of the herbivores, and a quality gradient of plant types. Herbivores can adapt by changing two adaptive traits: their level of specialization in feeding efficiency and their point of maximum feeding efficiency along the plant gradient. The number of herbivore phenotypes, their levels of specialization, and the amount of character displacement among them are the result of the evolutionary dynamics, which is driven by the underlying population dynamics, which in turn is driven by the underlying foraging behavior. Our analysis demonstrates broad conditions for the diversification of a herbivore population into many specialized phenotypes, for basically any foraging behavior focusing use on highest gains while also including errors. Our model predicts two characteristic phases in the adaptation of herbivore phenotypes: a fast character-displacement phase and a slow coevolutionary niche-shift phase. This two-phase pattern is expected to be of wide relevance in various consumer-resource systems. Bringing together ecological character displacement and the evolution of specialization in a single model, our study suggests that the foraging behavior of herbivorous arthropods is a key factor promoting specialist radiation.

Illegal births and legal abortions – the case of China

Abstract: China has a national policy regulating the number of children that a woman is allowed to have. The central concept at the individual level application is "illegal pregnancy". The purpose of this article is to describe and problematicize the concept of illegal pregnancy and its use in practice. Original texts and previous published and unpublished reports and statistics were used. By 1979 the Chinese population policy was clearly a policy of controlling population growth. For a pregnancy to be legal, it has to be defined as such according to the family-level eligibility rules, and in some places it has to be within the local quota. Enforcement of the policy has been pursued via the State Family Planning (FP) Commission and the Communist Party (CP), both of which have a functioning vertical structure down to the lowest administrative units. There are various incentives and disincentives for families to follow the policy. An extensive system has been created to keep the contraceptive use and pregnancy status of all married women at reproductive age under constant surveillance. In the early 1990s FP and CP officials were made personally responsible for meeting population targets. Since 1979, abortion has been available on request, and the ratio of legal abortions to birth increased in the 1980s and declined in the 1990s. Similar to what happens in other Asian countries with low fertility rates and higher esteem for boys, both national- and local-level data show that an unnaturally greater number of boys than girls are registered as having been born. Defining a pregnancy as "illegal" and carrying out the surveillance of individual women are phenomena unique in China, but this does not apply to other features of the policy. The moral judgment concerning the policy depends on the basic question of whether reproduction should be considered as an individual or social decision.

Adaptive dynamics as a mathematical tool for studying the ecology of speciation processes.

Abstract: After Ernst Mayr published his seminal book in 1963 (Mayr, 1963), the issue of speciation appeared to be settled: according to the established dogma, biological diversification occurred in allopatry due to the accumulation of genetic differences in geographically isolated populations. Despite repeated challenges, this view still prevails today, although perhaps less dominantly than before. The earliest rigorous theoretical challenge was provided by Maynard Smith (1966), who produced the first models of speciation in sympatry. These models were based on very simple ecological and genetic assumptions, with two resource types (or niches) and two loci, one for ecological performance and one for mate choice. Despite its simplicity, this type of model has formed the conceptual basis for most of the theory of sympatric speciation that has been developed since then (Kawecki, 2004). For sympatric speciation to occur in sexual populations, two processes must unfold. First, frequencydependent interactions must generate disruptive selection. Second, a lineage split in sexual populations requires the evolution of assortative mating mechanisms. Skepticism towards the feasibility of both these processes has led to a dismissal of sympatric speciation as a plausible mode of diversification. For example, based on Felsenstein’s (1981) seminal paper, it has long been thought that recombination between traits under disruptive selection and mating traits responsible for assortativeness can be a significant hindrance to the evolution of reproductive isolation between diverging lineages. Similarly, one of the main reasons why the theoretical developments following in the footsteps of Maynard Smith’s model failed to convince speciation researchers was that these models seemed to rely on rather particular ecological circumstances, such as host race formation (Diehl & Bush, 1989), and that the ecological conditions for the emergence of disruptive selection in these models were rather restrictive (Kassen, 2002; Kawecki, 2004). However, there is another line of thinking about the ecology of speciation that already started – how else could it be? – with Darwin, who concluded: Consequently, I cannot doubt that in the course of many thousands of generations, the most distinct varieties of any one species [...] would always have the best chance of succeeding and of increasing in numbers, and thus of supplanting the less distinct varieties; and varieties, when rendered very distinct from each other, take the rank of species. (Darwin, 1859, p. 155) According to this view, and in modern parlance, frequency-dependent competition between similar ecological types can lead to disruptive selection and diversification. This perspective was embodied in the concept of competitive speciation by Rosenzweig (1978) and further studied by Seger (1985), who presented the first mathematical model showing that frequency-dependent competition for occupation of a niche continuum can induce sympatric speciation under certain conditions. More generally, it was argued by Kondrashov (1986) that frequency-dependent selection on a continuous character can induce bimodal splits in the character distribution, with the two modes representing emerging species. In Kondrashov’s models, the disruptive selection regime giving rise to bimodality is simply a consequence of the a priori assumption that the fitness of common types is low, while that of rare types is high. It is difficult to assess the generality of these models, because it is not clear under what conditions ecological interactions would generate such a frequency-dependent selection regime. In fact, it is known that both competitive interactions (Christiansen, 1991) and predator-prey interactions (Abrams et al., 1993) can generate evolutionary scenarios in which the population mean of a continuous trait (such as body size) evolves to a state in which selection becomes disruptive. However, somewhat surprisingly, these results were never put into the common context of speciation, perhaps because these studies used the framework of quantitative genetics and thus assumed Gaussian phenotype distributions with constant variances (and hence implicitly assumed random mating). Overall, it thus remained questionable whether the emergence of disruptive selection due to frequencydependent interactions would be a general and plausible ecological scenario. In fact, it still seems to be the common wisdom that the origin and maintenance of diversity due to frequency-dependent selection regimes requires a delicate balance of different ecological factors (e.g. Kassen, 2002), and that, consequently, most biological diversification occurs in allopatry. We believe that the advent of adaptive dynamics, and in particular the discovery of the phenomenon of evolutionary branching, will change this perspective fundamentally (Dieckmann et al., 2004). Adaptive dynamics is a general framework for studying evolution of quantitative characters due to frequency-dependent interactions. Within this framework, evolutionary branching points Correspondence: Michael Doebeli, Department of Zoology and Mathematics, University of British Columbia, 6270 University Boulevard, Vancouver, BC, Canada V6T 1Z4. Tel.: +1-604-822-3326; e-mail: doebeli@zoology.ubc.ca

The GAINS Model for Greenhouse Gases - Version 1.0: Nitrous Oxide (N2O)

Abstract: Many of the traditional air pollutants and greenhouse gases have common sources, offering a cost-effective potential for simultaneous improvements of traditional air pollution problems and climate change. A methodology has been developed to extend the RAINS integrated assessment model to explore synergies and trade-offs between the control of greenhouse gases and air pollution. With this extension, the GAINS (GHG-Air pollution INteraction and Synergies) model will allow the assessment of emission control costs for the six greenhouse gases covered under the Kyoto Protocol (CO2, CH4, N2O and the three F-gases) together with the emissions of air pollutants SO2, NOx, VOC, NH3 and PM. This report describes the first implementation (Version 1.0) of the model extension model to incorporate N2O emissions. GAINS Version 1.0 assesses the options for reducing N2O emissions emissions from the various source categories. It quantifies for 43 countries/regions in Europe country-specific application potentials of the various options in the different sectors of the economy, and estimates the societal resource costs of these measures. Mitigation potentials are estimated in relation to an exogenous baseline projection that is considered to reflect current planning. In Europe, emissions from soils are generally considered the most important source of N2O, followed by industrial process emissions. Formation of nitrous oxide in soil is triggered by the availability of nitrogen. A number of emission controls directed at other pollutants (e.g., NOx or CH4) have positive or negative impacts on N2O emissions. Some of the earlier projections of N2O emissions have not taken full account of these interactions. Recent information on technological changes (e.g., for some technological processes) indicates a significant decline in N2O emissions in the past years, especially from adipic and nitric acid production. Catalytic reduction of N2O from industrial processes (adipic and nitric acid production), optimizing sewage treatment, modifications in fluidized bed combustion, and reduction of fertilizer application in agriculture can reduce N2O at moderate costs. Current legislation in EU countries addresses only some of these measures, which leaves an additional potential for further mitigation. However, the remaining mitigation potential is associated with high or even excessive costs. N2O emissions from non-agricultural soils induced from the atmospheric deposition of NOx and NH3, though of clearly anthropogenic origin, have not been counted as anthropogenic emissions by the Intergovernmental Panel on Climate Change (IPCC) methodology. However, the inclusion of such emissions to obtain full coverage of man-made N2O flows would not strongly alter N2O emissions from European countries.