A neurochemical approach to valuation sensitivity over gains and losses

Prospect theory proposes the hypothesis that people have diminishing sensitivity in valuing increases in the size of monetary outcomes, for both gains and losses. For decision-making under risk, this implies a tendency to be risk-tolerant over losses while being generally risk averse over gains. We offer a neurochemistry-based model of the diminishing valuation sensitivity hypothesis. Specifically, we propose that dopamine tone modulates the sensitivity towards valuation of gains while serotonin tone modulates the sensitivity towards valuation of losses. Consequently, higher dopamine tone would yield a more concave valuation function over gains while higher serotonin tone would yield a more convex valuation function over losses. Using a neurogenetics strategy to test our neurochemical model, we find that subjects with the 9-repeat allele of DAT1 (lower DA tone) are more risk-tolerant over gains than subjects with the 10-repeat allele, and that subjects with the 10-repeat allele of STin2 (higher 5HT tone) are more risk-tolerant over losses than subjects with the 12-repeat allele. Overall, our results support the implications of our model and provide the first neurogenetics evidence that risk attitudes are partially hard-wired in differentiating between gain- and loss-oriented risks.     

生物保护的经济学

生物保护研究已经从保护生物学发展到保护生态学,在社会经济因素对自然保护影响日益广泛深刻的今天,我们应该更加主动地从经济学角度进行生物多样性保护。建立自然保护区是生物多样性就地保护的重要措施之一。目前的自然保护区管理研究基本上是以生物学和生态学为主,缺乏系统的经济学考虑,导致一些自然保护区的管理效果不理想,可持续性受到威胁。本文在回顾生物保护的相关经济学研究的同时,提出保护经济学的概念和研究框架,以期为自然保护区的经济管理提供一种新思路,为管理部门的保护投资决策提供支持。     

The reproductive value in distributed optimal control models

We show that in a large class of distributed optimal control models (DOCM), where population is described by a McKendrick type equation with an endogenous number of newborns, the reproductive value of Fisher shows up as part of the shadow price of the population. Depending on the objective function, the reproductive value may be negative. Moreover, we show results of the reproductive value for changing vital rates. To motivate and demonstrate the general framework, we provide examples in health economics, epidemiology, and population biology.     

Sperm competition and ejaculate economics

Sperm competition was identified in 1970 as a pervasive selective force in post‐copulatory sexual selection that occurs when the ejaculates of different males compete to fertilise a given set of ova. Since then, sperm competition has been much studied both empirically and theoretically. Because sperm competition often favours large ejaculates, an important challenge has been to understand the evolution of strategies through which males invest in sperm production and economise sperm allocation to maximise reproductive success under competitive conditions. Sperm competition mechanisms vary greatly, depending on many factors including the level of sperm competition, space constraints in the sperm competition arena, male mating roles, and female influences on sperm utilisation. Consequently, theoretical models of ejaculate economics are complex and varied, often with apparently conflicting predictions. The goal of this review is to synthesise the theoretical basis of ejaculate economics under sperm competition, aiming to provide empiricists with categorised model assumptions and predictions. We show that apparent contradictions between older and newer models can often be reconciled and there is considerable consensus in the predictions generated by different models. We also discuss qualitative empirical support for some of these predictions, and detail quantitative matches between predictions and observations that exist in the yellow dung fly. We argue that ejaculate economic theory represents a powerful heuristic to explain the diversity in ejaculate traits at multiple levels: across species, across males and within individual males. Future progress requires greater understanding of sperm competition mechanisms, quantification of trade‐offs between ejaculate allocation and numbers of matings gained, further knowledge of mechanisms of female sperm selection and their associated costs, further investigation of non‐sperm ejaculate effects, and theoretical integration of pre‐ and post‐copulatory episodes of sexual selection.     

Neglect of biological riches: the economics of nature tourism in Nepal

Nepal's spectacular parks and reserves have attracted dramatically increasing numbers of foreign visitors. It might be expected that these protected areas would be nurtured as valuable and irreplaceable economic assets. However they are becoming seriously degraded and the financial resources provided for their management have been inadequate. This paper explores why — starting with the hypothesis that so little of the economic value of protected area tourism in Nepal is captured through fees and other charges assessed on foreign visitors that the protected areas are perceived as being of inconsequential value. It is conservatively estimated that $27 million of tourists' total expenditure in Nepal were attributable to the protected area network in 1988, when the costs of managing the parks were less than $5 million but direct fees colleeted from tourists visiting the protected areas amounted to less than $1 million. These figures suggest the parks are a good investment. But it could also be argued that the costs of park management were more than five times the revenues collected by the government from park tourists. Policy measures are identified which could help Nepal increase the economic as well as environmental benefits from nature tourism.Case studies of Nepal's most-visited protected areas emphasize that the lack of funds for protected area management is not the only constraint on effective management. Some important economic and institutional interests have yet to be effectively reconciled with conservation in the protected areas. Most problematic are local people's economic aspirations and the operating practices of the principal government agencies involved — the Department of National Parks and Wildlife Conservation and the Ministry of Tourism. Fortunately there have recently been some encouraging signs of change within both of these agencies.     

Leaf angle as a leaf and canopy trait: Rejuvenating its role in ecology with new technology

Life on Earth depends on the conversion of solar energy to chemical energy by plants through photosynthesis. A fundamental challenge in optimizing photosynthesis is to adjust leaf angles to efficiently use the intercepted sunlight under the constraints of heat stress, water loss and competition. Despite the importance of leaf angle, until recently, we have lacked data and frameworks to describe and predict leaf angle dynamics and their impacts on leaves to the globe. We review the role of leaf angle in studies of ecophysiology, ecosystem ecology and earth system science, and highlight the essential yet understudied role of leaf angle as an ecological strategy to regulate plant carbon–water–energy nexus and to bridge leaf, canopy and earth system processes. Using two models, we show that leaf angle variations have significant impacts on not only canopy-scale photosynthesis, energy balance and water use efficiency but also light competition within the forest canopy. New techniques to measure leaf angles are emerging, opening opportunities to understand the rarely-measured intraspecific, interspecific, seasonal and interannual variations of leaf angles and their implications to plant biology and earth system science. We conclude by proposing three directions for future research.     

Strengthening protected-area management: a focus for the 1990s,a platform for the future

This paper aims at an objective evaluation of the purpose, management and effectiveness of protected areas. It questions accepted dogma and poses broad challenges that need to be resolved, in order to enter the next century with a more secure, efficient and meaningful global network of parks and reserves. It also suggests the need for protected-area managers to form themselves into a discrete, focused, professional discipline, emancipated from the noise created by a professionalism borrowed from a range of other disciplines. This is central to addressing the mounting challenges facing protected areas, if they are to survive and fulfill the purposes expected of them.     

Optimal fishery policy for size-specific,density-dependent population models

Optimal harvest policy is derived for a size-specific population model based on the continuity equation. In this model both growth and recruitment rates can depend on either the number of individuals of specific sizes in the population or the level of food available. Necessary conditions for values of fishing pressure and size limit that maximize the present value of the resource are obtained and are interpreted in economic terms. The general solution obtained here reduces to solutions obtained previously for some special cases: the single age-class model, and the linear age-dependent model. Solutions involving constant fishery policy are sought for several different, specific versions of the general model. In each of these versions a constant policy solution is not optimal. This implies that for a general, realistic model the policy that maximizes present value is a time-varying or pulse fishing policy. The theoretical and practical implications of the results are discussed in the light of existing results.     

Bioaugmentation for enhancing biological wastewater treatment

The literature on bioaugmentation products has been reviewed. Their manufacture and method of use is explained. The various applications are listed and the independent investigations, as opposed to manufacturers accounts, at laboratory and full scale are reviewed. The economics and kinetic modelling are also discussed. In laboratory investigations bioaugmentation often failed, whereas at full scale it was often successful, probably due to the imposition of steady state at laboratory scale. Most products require a period of acclimatisation before working; this and other possible reasons for failure are discussed.     

Estimate of Yield Loss from the Citrus Nematode in Texas Grapefruit

Chemical control of the citrus nematode, Tylenchulus semipenetrans Cobb, has consistently increased yield of grapefruit on sour orange rootstock in Texas. In this study, data from chemical control tests conducted from 1973 to 1980 were analyzed to determine the relationship between nematode counts and grapefruit yield and fruit size. The correlation between yield and nematode counts was negative (r = -0.47) and highly significant (P < 0.01). The data best fit the exponential decay curve: y = 160.3e^-0.0000429 where y = yield in kg/tree and x = nematodes/100 cm³ of soil. The correlation between fruit size and nematode counts was not significant because yield and fruit size were inversely related. Yield loss in an average untreated orchard was estimated to be 12.4 tons/ha. Economic loss to citrus nematode in Texas grapefruit, assuming no treatment and an average on-tree price of $60/ton, was estimated to be $13.2 million annually.