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.     

A proactive approach for assessing alternative management programs for an invasive alien pollinator species

Most evaluations of the economic impacts of invasive species are done post facto and concentrate on direct production loss caused. However, the effects of invasive species on non-market services such as biodiversity and landscapes can be considerable. A proactive approach of assessing the expected economic impact of invasive species prior to their occurrence may contribute to greater efficiency of policy makers. Here we used a stated preference method for a priori evaluating the willingness of the population to pay for different control programs of a new invasive bee species in Israel, the dwarf honey bee, Apis florea. We evaluated possible economic impacts of A. florea using two model plant species expected to be adversely affected by its invasion due to decreased pollination. The plants have no market value but they add aesthetic value to the open landscape. Using a mixed logit model we found that the mean willingness to pay (WTP) differed between the model plants, and increased with the extent of plant loss. Respondents differentiated between levels of damage to the plants and between control methods in their preferences for a specific program. Our results provide means for informed proactive decision making in preventing the continued invasion of the bee.     

Control and the management of a spreading invader

We consider the problem of management of an aquatic invader spreading in a lake system. We assume that each year the invader can be removed from a certain proportion of invaded lakes, which depends on the selected intensity of control. Control decisions are generated and compared for an optimally controlled system and for a static optimization across asymptotic steady states. Control close to eradication of the invasive species is always optimal for invasions with relatively high damages, low rates of density dependent spread and/or low chance of additional random introductions. Control to a highly invaded steady state is optimal for those invasions with low relative damages, high chances of random introduction and high levels of uncertainty in species location. In all other cases the optimal outcome depends upon initial conditions. Comparing the relative performance of the optimally controlled system and the static optimization demonstrates situations when the differences are small and when not. When invasions are acted upon in their later stages and across certain parameter combinations a static optimization provides a reasonable approximation of an optimally controlled system. The flip-side is that optimal policies directed at an invasion in its early stages tend to provide significantly savings. The savings vary across parameter combinations, yet in these situations little useful insight will be generated without consideration of a dynamically optimized system.     

濒湖旅游区开发思考——以江苏省环太湖旅游区为例

湖泊是我国重要的旅游资源,但是作为湖泊旅游重要内容的濒湖旅游区开发往往存在没有整体规划、缺乏统一形象、低水平重复开发、生态环境恶化等问题。针对这种现实,提出了整体开发、多样化、集团化、可持续发展等濒湖旅游区开发原则,并以环太湖旅游区为例,在创立“太湖旅游”品牌的前提下,探讨了其定位、形象、综合治理和可持续发展战略等问题,为濒湖旅游区的开发提供了新的思考范式。     

防治外来生物入侵的法律对策思考

外来入侵物种是指从自然分布区通过有意或无意的人为活动而被引入,在当地的自然或半自然生态系统中形成了自我再生能力、给当地的生态系统或景观造成明显的影响的物种。外来入侵物种在当地定植、①扩展并产生一定影响的过程称为生物入侵。它们对入侵地的生态安全、经济发展以及人类健康造成了巨大的生态灾难和经济损失,因此,引起了人们广泛的关注。然而,由于缺乏对入侵生物的综合性认识,对于控制入侵生物措施的研究也才刚刚起步,还没有系统的控制外来入侵生物的有关程序与法规。为了保护中国的生物多样性,维护生态安全,亟须加快中国在这一领域的立法步伐。     

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.     

城市居民环境友好行为意向形成机制的性别差异

利用在海口市的调查数据,分析环境友好行为意向形成的性别差异。结果发现：①女性报告的环境友好行为意向强于男性;②影响男女环境友好行为意向形成的因素不同,产生机制也不同。环境敏感度、环境态度、反应效能感是男性环境友好行为意向的预测因子,后果意识对男性的环境友好行为意向形成具有调节作用;环境敏感度、环境行动知识、反应效能感与后果意识是女性环境友好行为意向的预测因子;在特定条件下,环境行动知识对女性的环境友好行为意向形成具有调节作用。研究结果能为居民环境教育,尤其是进行性别差异化教育提供科学依据。     

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。     

Beyond the lamppost: Optimal prevention and control of the Brown Tree Snake in Hawaii

We develop an integrated model for the prevention and control of an invasive species. The generality of the model allows its use for both existing and potential threats to the system of interest. The deterministic nature of arrivals in the model enables clear examination of the tradeoffs inherent when choosing between prevention and control strategies. We illuminate how optimal expenditure paths change in response to various biological and economic parameters for the case of the Brown Tree Snake in Hawaii. Results suggest that it is more advantageous to spend money finding the small population of snakes as they occur than attempting to prevent all future introductions. Like the drunk that looks for his keys only where the light is, public policy may fail to look “beyond the lamppost” for snakes that have already arrived but have not yet been detected. Actively searching for a potential population of snakes rather than waiting for an accidental discovery may save Hawaii tens to hundreds of millions of dollars in future damages, interdiction expenditures, and control costs.     

Willingness to pay for other species' well-being

Benefit-cost analysis of environmental policies typically focuses on benefits to human health and well-being. For other species, economists have attempted to measure human WTP for changes in the numbers of individuals for different types of wildlife, and to preserve biodiversity. When it comes to humans' WTP for improvements in the quality-of-life for other species, however, the evidence is limited. Morbidity and quality-of-life considerations may be particularly important to the task of valuing non-fatal harm to wildlife in the wake of an environmental disaster. We argue that the other species morbidity-reduction component of WTP should be calculated net of any “outrage” component associated with the cause of the harm. This net WTP is likely to be correlated with the premium that people are willing to pay for chicken products from birds for which the quality-of-life has been enhanced by improved animal welfare measures. This paper uses a conjoint choice stated preference survey to reveal the nature of systematic heterogeneity in preferences for “humanely raised” versus “conventionally raised” chicken. We also use latent class analysis to distinguish between two classes of people—those who are willing to pay a premium for humanely raised chicken, and those who are not.     

A model for estimating fish population and optimal fishing effort in lakes and rivers

We developed a model for estimating the fish population for various species in lakes and rivers. Our estimation focuses, in its first step, on fish species that breed outside the lake. Using the annual outside supply of fingerlings, natural survival rate and reported amounts of fish caught, we estimated fish stock. Given the estimated stock for fish bred outside the lake, we can evaluate the catch rate. Assuming equal catch rates for other species, and given the amount caught for each species, we are able to evaluate each species stock. Using the proposed technique, we evaluated various species stocks in the Sea of Galilee (Lake Kinneret) in Israel. Using our suggested technique for evaluating fish stock, we calculated the optimal effort of fishing needed for maximizing steady state profit of the fishers.     

Importing exotic plants and the risk of invasion: are market-based instruments adequate?

Exotic plant species are often intentionally imported into regions outside of their normal range as ornamental plants or as breeding stock, thereby generating benefits for consumers and producers. However, one of the unintended side effects of such introductions is that the exotic plant species may become invasive. Prohibiting sale of this type of exotic plant species, on the basis that it may become invasive, will have social costs in the form of foregone consumer benefits and nursery profits. We develop a model of a private commercial plant breeding industry that imports an exotic plant species into a region. The risk associated with invasion is modeled using a probabilistic ‘hazard function’, the key determinants of which are the characteristics of the exotic plant and the number of commercial nurseries contributing to its dispersal. We consider the possibility of employing market-based instruments (e.g., Pigovian tax) consistent with the concept of ‘introducers pay’, to regulate the nursery industry. We then provide an empirical illustration using the historical introduction of saltcedar (Tamarisk spp.) into the United States. Our results indicate that the mere presence of a risk of invasion does not mean that it is socially optimal to prevent commercial sales of an exotic plant species. Indeed, there appear to be plausible forms of the functional relationships involved that require only a modest reduction in the private industry optimum. In contrast, no sales of the exotic plant should occur at all under several sets of assumptions about the level of invasion risk and the linkage between dispersal sites and invasion hazard.     

Spatially optimal habitat management for enhancing natural control of an invasive agricultural pest: Soybean aphid

By their direct effects on private profitability, invasive agricultural pests create special incentives for management that set them apart from other categories of invasive species. One attractive nonchemical management approach for agricultural pests relies upon biological control by natural enemies. By improving the habitat of natural enemies of invasive agricultural pests, biological pest control can become privately attractive. This study develops a spatial optimization model to explore economically optimal spatial configuration of natural enemy habitat in agricultural landscapes. The model is applied to the management of soybean aphid (Aphis glycines), a recent invasive pest species of soybean production systems in the North Central region of the United States. Results indicate that non-crop habitat management can be a promising pest management option for organic cropping systems. Under current prices, however, habitat management tends to reduce net returns for conventional farms. Both area and configuration of non-crop habitats affect economic performance, with the greatest value coming from small, scattered areas of habitat.     

The Asian clam Corbicula fluminea in the European freshwater-dependent industry: A latent threat or a friendly enemy?

While the biofouler Corbicula fluminea (Müller, 1774) is known to cause great economic losses in North America, studies reporting the problem in Europe are much scarcer. This paper explores the industrial effects of the species in Portugal, the gateway by which the bivalve entered Europe around 30 years ago. National waterworks, major power stations, cement plants, pulp and paper mills and irrigation systems were surveyed. The industrial impacts of the pest were shown to remain relatively mild; irrigation systems are those that seem to be facing more significant economic losses due to infestation. Possible reasons for the apparent discrepancy between this result and the species dispersal in natural ecosystems are discussed, and recommendations on adequate responses to the latent threat are provided. This study may assist the implementation of integrated pest management policies in countries at risk of invasion or recently invaded, and contribute to an understanding of the species’ progression in industrial environments.     

When is a “wait and see” approach to invasive species justified?

Predictions of damages and damages that might be avoided from invasive species control policies are marred by uncertainty that has both economic and ecological roots. Public policies directed at invasive species typically lag their detection. One possible explanation is the coupling of uncertainty with political and economic commitments creates an incentive to delay a policy response in order to gain more information on how damaging the invasion will be – a “wait and see” approach. We investigate whether this rationale is justified by identifying invasion characteristics that require the wait and see approach often adopted by lawmakers and government agencies. The model shows that the source of uncertainty and degree of policy irreversibility matter and allows the classification of invasive species with a low rate of spread and low levels of uncertainty as those where policies can be optimally timed in the future.     

Harvest and extinction in multi-species ecosystems

A potential cost of harvesting in multi-species ecosystems is the extinction of nonharvested species that are at the same trophic level as the harvested species. Existing analytical models are not well-suited for studying this harvest externality because they focus on species interactions across trophic levels instead of within them. We identify the conditions under which the harvesting of a single species causes at least one extinction of nonharvested species at the same trophic level. We compare two harvest regimes: uniform management, in which a privately optimal harvest rate is applied to the entire ecosystem; and specialized management, in which a portion of the ecosystem is intensively managed for the harvested species and the rest is left unharvested. Which regime is more likely to result in extinction depends on the discount rate and on the harvested species' competitive ability and colonization rate compared to those of the other species.     

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.     

武汉中心城区湖泊公园服务范围与优化 调控研究

城市居民对城市水体的游憩需求日渐强烈,而目前尚未有明确可行的办法指导城市湖泊等水体的功能定位与其布局的优化调控。通过GIS建立以道路网络为基础的交通网络数据库,以及包含湖泊面积、入口、名称等的湖泊(公园)数据库,分析得出建成和潜在的湖泊公园的游憩服务范围,并与基于实证调研计算的服务范围进行对比,验证了其有效性。通过游憩服务半径分析计算,得出步行服务盲区、车行服务盲区、真空盲区和隐形盲区4种服务盲区类型,与盲区用地性质和自然条件共同指导湖泊公园的优化调控和城市湖泊的功能定位。研究结果表明,基于真空盲区和隐形盲区消除的湖泊公园优化调控策略有所不同,并在此基础上总结了对于湖泊公园规划建设的启示。运用GIS对湖泊公园服务范围进行分析,可切实将城市居民休闲需求与城市湖泊分布相结合,优化调控湖泊公园的空间布局。     

Unsafe sex,AIDS and development

The AIDS-fighting communities have spent their limited resource on improving people’s awareness of the risk of contracting AIDS, and yet these programs have not resulted in sustained behavior change. This paper offers a possible explanation of why agents in poor countries choose to engage in more unsafe sexual activities when they are perfectly cognizant of the risk involved. It is shown that agents may rationally choose to do so when they are poor, since future is not attractive due to poverty and agents care more about current-period utility. Our results indicate that safe sexual practice is essentially a “normal good” and that development may be key to reduce the HIV infectivity by modifying agents’ sexual behavior. The model is then extended to consider the role of public health expenditure. We find that the relationship between protected sexual activity and development is no longer monotonic: unsafe sexual activity may increase slightly after a critical level of development has been reached. Finally, we examine the impacts of AIDS on development by considering individual’s saving decision. It is shown that agents tend to save more and accumulate more capital when economy grows.