Identifying,preventing and controlling invasive plant species using their physiological traits

A model of a plant community that is biologically reasonable and easily adaptable to economic models is presented. The model includes optimization, competition, stochastic limiting resources, and identification of redundant and invasive species. Species exhibit a rich array of traits that make them suited for some set of environmental factors and not for other sets. And because environmental factors are constantly changing, species that are very successful under one set of factors become redundant under another set, implying that an ecosystem needs redundant species as insurance. Invasive species are the flip side of redundant species as they are successful, at least under some environmental conditions. Identification depends on four physiological parameters defining each plant: two respiration parameters, a parameter that gives the plant's ideal level of the stochastic limiting resource, and the specific leaf area. The parameters are terms in an expression that gives the net energy intake of an individual plant, and the plant behaves as if it optimizes this by choosing its individual biomass. Success of species is judged based on the biomass of the species in steady state. An application extends the range management literature by incorporating the model into a rangeland manager's decision problem extends the range management literature. The model allows for multiple plant species, addresses the influence of limiting resources (other than density dependence), and tracks the response of the entire system to human and natural system perturbations. The methods allow simple predictions of community composition in the face of jointly determined economic/ecological behavior. The power of the method is demonstrated through stylized examples of alternative invasion control techniques.     

Managing invasive alien species with professional and hobby farmers: Insights from ecological-economic modelling

Biosecurity is a great challenge to policy-makers globally. Biosecurity policies aim to either prevent invasions before they occur or to eradicate and/or effectively manage the invasive species and diseases once an invasion has occurred. Such policies have traditionally been directed towards professional producers in natural resource based sectors, including agriculture. Given the wide scope of issues threatened by invasive species and diseases, it is important to account for several types of stakeholders that are involved. We investigate the problem of an invasive insect pest feeding on an agricultural crop with heterogeneous producers: profit-oriented professional farmers and utility-oriented hobby farmers. We start from an ecological-economic model conceptually similar to the one developed by Eiswerth and Johnson [Eiswerth, M.E. and Johnson, W.S., 2002. Managing nonindigenous invasive species: insights from dynamic analysis. Environmental and Resource Economics 23, 319-342.] and extend it in three ways. First, we make explicit the relationship between the invaded state carrying capacity and farmers' planting decisions. Second, we add another producer type into the framework and hence account for the existence of both professional and hobby farmers. Third, we provide a theoretical contribution by discussing two alternative types of equilibria. We also apply the model to an empirical case to extract a number of stylised facts and in particular to assess: a) under which circumstances the invasion is likely to be not controllable; and b) how extending control policies to hobby farmers could affect both types of producers.     

Optimal fishery harvesting rules under uncertainty

This paper derives the optimal fishery harvest policy in a real-option model with a stochastic logistic growth process, harvest-sensitive output price, and both fixed and variable harvesting costs. The policy specifies the harvest trigger and harvest size, while outputs from the model include the value of the fishery and the risk of extinction. The optimal policy is illustrated with data from the Pacific Halibut Fishery. For this particular case, the optimal policy recommends harvesting when the fish stock rises to about three-quarters the environmental carrying capacity, and the amount harvested should be approximately a quarter of the prevailing stock. This harvesting policy maximizes the value of the fishery, and importantly, the resulting risk of extinction is negligible. We also carry out some sensitivity analysis to see how the optimal policy (and the resulting fishery value and risk of extinction) change when the input parameters are varied, particularly the ecological parameters intrinsic growth rate and volatility of the stock, and also the economic parameters that have been ignored in previous papers (price sensitivity and fixed cost). If the optimal policy is followed, the risk of extinction will be negligible, except for very low growth rate and high volatility.     

Factors determining awareness and knowledge of aquatic invasive species

Public perceptions of invasive species may influence policies and programs initiated by public and private stakeholders. We investigate the determinants of the public's awareness and knowledge of invasive species as few studies have examined this relationship. We focus on aquatic invasive species (AIS) and employ survey data from property owners in a lake district. A major contribution is that we estimate a mixed trivariate binary-ordered probit regression model that accommodates correlations among unobserved characteristics, produces statistically more efficient estimates, and allows a more proper investigation of the probability of knowledge conditional on awareness. Our results provide insights for invasive species education and management programs. We find that individuals are more likely to be aware of AIS if they participate in water-based recreation, visit lakes outside their area, have a boat, belong to a lake association, or are college educated. This has a policy implication: Given high levels of AIS awareness by those most involved in activities around lakes and those with a higher education, it may be beneficial to target informational campaigns at those who do not display these characteristics, so that they can better make informed decisions about whether to support and expend money on invasive species management programs.     

Invasive species management in a spatially heterogeneous world: Effects of uniform policies

The spread of invasive species (IS) is an inherently spatial process, and management of invasive species occurs over spatially heterogeneous regions, but policy constraints can restrict management responses to be homogeneous across regions. Using a spatial bioeconomic model that includes a representation of invasive species ecology based on heterogeneous environments that are linked across space and time by human and ecological pathways, we compare optimal spatially heterogeneous policy to spatially uniform policy. We explore the magnitude and pattern of the policy differences with emphasis on the influence of different types of underlying heterogeneity across locations.     

金融产业生态系统的生态承载力研究

借鉴生态系统的有关理论,提出了金融产业生态系统的生态承载力概念,界定了其时空、技术和社会经济内涵,分析了其演化的客观性、整体性和动态稳定性特征.重点分析了金融产业生态系统生态承载力的控制因素:经济金融资源承载力、产业生态环境承载力和系统生态弹性力.认为金融产业生态系统要可持续发展就必须考虑系统的生态承载力.     

Easter Island: historical anecdote or warning for the future?

Two standard solutions for the ‘Malthusian Trap’ involve institutional reforms and technological progress. Using Easter Island as an example, we investigate the hypothetical role that technological progress and population management reform might have played in preventing the collapse of the island's civilization. The model includes a composite manufactured good and a composite harvested renewable resource. Fertility is assumed to rise with per capita income. The resource's carrying capacity and intrinsic growth rate as well as labor's harvesting productivity are subject to technological progress. Fertility is subject to population management reform. The model yields a system of two simultaneous, nonlinear, non-autonomous differential equations. We first study the system's steady states. The system is then parameterized for Easter Island and its comparative dynamics are investigated in simulations. We find that technological progress can generate large fluctuations in population, renewable resources, and per capita utility, sometimes resulting in system collapse. With high fertility rates, the population and the resource vanish. None of the simulations investigated here exhibit a constantly growing per capita utility over time. Finally, we evaluate the applicability of these results to contemporary societies.     

An options based bioeconomic model for biological and chemical control of invasive species

The management of non-native invasive species is a complex but crucial task given the potential for economic and environmental damages. For many invasions the development of socially optimal control strategies requires more than is offered by the single-species, single-control models that have dominated this area of research. We develop a general stochastic optimal control framework that accommodates multiple interacting species while accounting for uncertainty in the temporal population dynamics. This extension to the current line of bioeconomic control models allows for the design of optimal integrated pest management strategies that utilize both chemical and biological controls in an environment of uncertainty and irreversibility. We demonstrate the benefits of combining chemical and biological controls in long term management strategies through a case study of the hemlock wooly adelgid (Adelges tsugae) infestation in the eastern United States. In this application we find that the introduction of natural predators is usually sufficient to manage the infestation, though chemical insecticides can play an important role when detection of the infestation is delayed or when the biological control agent does not sufficiently increase mortality of the invasive species.     

Maritime trade and migratory species management to protect biodiversity

Invasive species threaten biodiversity worldwide. Ships inadvertently carry marine invasive species to vulnerable ports. An empirical game theoretic analysis is presented to explore this transboundary biological pollution topic. This analysis utilizes data on marine invasive species and maritime trade as a vector of impact on native species at different public port locations along the Pacific coast of the North American countries. Preventative and reactive abatement strategies are compared. The countries are not identical and a comparison of noncooperative game strategies and payoffs to the cooperative game is presented. With the asymmetry between countries, optimal sharing rules are quantified. Results show that cooperative and preventative abatement is optimal compared to all other strategies dealing with stock and flow pollution.      

Indirect management of invasive species through bio-controls: A bioeconomic model of salmon and alewife in Lake Michigan

Invasive species are typically viewed as an economic bad because they cause economic and ecological damages, and can be difficult to control. When direct management is limited, another option is indirect management via bio-controls. Here management is directed at the bio-control species population (e.g., supplementing this population through stocking) with the aim that, through ecological interactions, the bio-control species will control the invader. We focus on stocking salmon to control invasive alewives in Lake Michigan. Salmon are valuable to recreational anglers, and alewives are their primary food source in Lake Michigan. We illustrate how stocking salmon can be used to control alewife, while at the same time alewife can be turned from a net economic bad (having a negative shadow value) into a net economic good (having a positive shadow value) by providing valuable ecosystem services that support the recreational fishery. Using optimal control theory, we solve for a stocking program that maximizes social welfare. Optimal stocking results in cyclical dynamics. We link concepts of natural capital and indirect management, population dynamics, non-convexities, and multiple-use species and demonstrate that species interactions are critical to the values that humans derive from ecosystems. This research also provides insight into the management of salmon fisheries in the Great Lakes.     

谨防物种地理入侵维护区域经济可持续发展

人类历史上外来物种的地理引入对区系经济发展有过积极的作用,由于物种地理引入过程中的“入侵”机制,使得引入种不但不能增加原生地生物区系的物种种类,反而减少了它的生物多样性,加速了原生生物区系的物种灭绝速度,引发水土流失,恶化人类生存环境,增大难以逆转的经济损失隐患,进而制约区域经济的可持续发展,对区域经济可持续发展可能会造成严重的潜在危害。为了维护区域经济的可持续发展,必须谨防物种地理入侵。     

Optimal detection strategies for an established invasive pest

We model optimal detection of sub-populations of invasive species that establish ahead of an advancing front. For many invaders, eradication of the main population is an untenable goal, yet it may be possible to treat and eradicate emerging sub-populations once these sub-populations are detected. We embed a dynamically optimal post-detection management plan of sub-populations into a model of optimal detection effort determination and find that optimal detection effort depends, in part, on the distance from the main front: locations closer to the front with shorter management horizons enjoy lower reductions in overall cost from intervention. The uninfested landscape is divided into two zones, characterized by different dynamically optimal management plans: a suppression zone and an eradication zone. In the suppression zone, optimal detection effort increases with distance from the front. At the distance where the suppression zone yields to the eradication zone, optimal detection effort plateaus at its maximum level.     

旅游生态环境承载力计算方法研究

旅游环境承载力的评估是实现对生态旅游景区合理规划、有效管理,最终实现可持续发展必不可少的工具。本文运用生态学研究中生态足迹的概念和方法,通过分析生态旅游区的生态足迹的供给与需求,建立了基于生态足迹的环境承载力评估模型。     

云南山区生态农业产业发展思路与对策

山区农业是云南农业发展的一大难题,资源开发与生态环境问题一直是西部开发战略的核心,实现经济与环境持续发展,在生态系统承载能力范围内,充分发挥生态优势,依托地域优势,采用积极有效的经营机制,对提高农业生态系统生态能力,实现生态、经济和社会效益具有重要的意义,也是解决＂三农＂问题,建立和谐社会主义新农村必须面对的问题。面对云南山区农业令人担忧的现状,以生态农业产业为出发点,对云南山区生态农业的发展进行分析,提出了发展云南山区生态农业产业的基本思路和对策。     

The value of nonindigenous species risk assessment in international trade

Managing the introduction of nonindigenous species is becoming a major goal of policy-makers at regional, national and international scales. Here we investigate, at the national level, the ideal design and expected net benefits of a risk assessment program for evaluating the desirability of nonindigenous species imports. We show how to enhance the statistical rigor of such a system by correcting a common non-random sampling problem encountered in the data. This correction enables model output to be interpreted in an economically relevant way and facilitates a theoretically rigorous characterization of the balance between trade and nonindigenous species establishment risk. Using reptiles and amphibians imported to the U.S. as a case study, we characterize economic outcomes over a range of cases and demonstrate substantial expected returns to such a screening program, relative to the current effectively open-door policy. Our results are informative for the current debate in the U.S. about whether to require federal agencies to apply risk assessment before allowing a species for import. The framework presented decomposes a complex argument about risk management into component economic and statistical parts, allowing for debate and improved understanding over each element to inform the overall program in a transparent fashion.     

Optimum reserve size,fishing induced change in carrying capacity,and phenotypic diversity

Fish stocks around the world are heavily overexploited in spite of fishing policies in several parts of the world designed to limit overfishing. Recent studies have found that the complexity of ecological systems and the diversity of species, as well as negative impact of fishing activities on environmental carrying capacity of fish stocks—all contribute to the problem. A number of biologists, managers, and practitioners strongly support the use of marine reserves as a management strategy for marine conservation. This paper contributes to this line of research by seeking an optimum reserve size and fishing effort for situations where species diversity decrease at fishing grounds and fishing activities impact carrying capacity. We found that a reserve size which maximizes economic rents could ruin a fish stock if fishing impacts are not accounted for. On the other hand, the reserve serves as a bifurcation term which could improve the resilience of a marine ecosystem.     

Shark hunting: On the vulnerability of resources with heterogeneous species

This paper examines the unprecedented decimation of sharks. In accordance with the biological characteristics and the economic environment of sharks, we extend the Brander-Taylor model of renewable resources and trade to a resource with a continuum of species which are heterogeneous with respect to their growth rate. The model implies that heterogeneity increases the vulnerability of a resource as relatively abundant species make harvesting economically viable even though slow-growing species are driven to extinction. The empirical analysis assesses the fate of sharks in the light of the model and finds that the likelihood of extinction is, indeed, significantly greater for shark species which exhibit low intrinsic growth.     

The animal spirits hypothesis and the Benhabib–Farmer condition for indeterminacy

This paper provides a self-contained review of the introduction of the animal spirits hypothesis into the infinite horizon optimal‐growth model. The analysis begins with an economic discussion of Pontryagin's maximum principles. Thereafter, I develop a version of the increasing-returns Benhabib–Farmer model by showing the possible sub-optimality of the central planner solution and deriving the bifurcation condition for indeterminacy. Moreover, I give some insights on how to model intrinsic and extrinsic uncertainty. Finally, analyzing the equilibrium condition of the labor market, I provide an intuitive rationale for the mechanism that in this model might lead prophecies to be self-fulfilling.     

资源约束条件下人口城市化模式研究

从资源供给的角度看,人口城市化模式取决于一个地区实际人口与资源承载人口的关系.而区域资源承载人口取决于生态、经济和自然等多种资源的综合承载人口,且资源承载人口是动态的,是生产力的函数,自然资源承载是基础,经济承载是关键,生态承载是限制.本文探讨了资源承载人口的计算方法和模型,运用该模型对吉林省四平市2003年的承载人口进行了测算,分析了现实人口与承载人口的关系.在此基础上,探讨了人口城市化的模式.旨在达到区域土地供给约束、人居需求扩大和城市经济增长的三项式关系的平衡,使我国人口城市化可持续发展.     

支撑力和压力脱钩视角下中国生态承载力评价

提高生态承载力是生态文明建设的重要抓手之一,准确评价生态承载力是前提。文章基于大气、水和土壤三个生态环境层面的自净能力和污染水平视角,采用生态支撑力和压力脱钩模型,测度和评价了中国生态承载力状况。首先基于生态支撑力和压力脱钩类型构建了生态承载力评价框架,将生态承载力类型分为上升和下降两大类,每一大类有包含三个小类型。其次,采用脱钩模型对各地区总体和大气、水、土壤三个分类的生态承载力进行了测度,结果表明,整体生态承载力和分类生态承载力都呈现水平偏低,区域间和区域内差异明显和波动大的特征;西部地区的云南和新疆生态环境质量最好,而北京、湖南和四川生态环境质量相对较差。最后,文章从优化顶层设计、制定差异性生态环境保护和污染治理政策方面提出了提高生态承载力的政策参考。