Simulation model of a predator-prey system comprised ofPhytoseiulus persimilis andTetranychus urticae. II. Model sensitivity to variations in the life history parameters of both species and to variations in the functional response and components of the numerical response

Summary A detailed sensitivity analysis of a model of a predator-prey system comprised ofTetranychus urticae andPhytoseiulus persimilis was performed. The aim was to assess the relative importance of the life history parameters of both species, the functional response, and the components of the numerical response. In addition, the impact of the initial predator-prey ratio and the timing of predator introduction were tested. Results indicated that the most important factors in the system were relative rates of predator and prey development, the time of onset of predator oviposition, and the mode of the predator's oviposition curve. The total oviposition of the predator, the effect of prey consumption on predator oviposition, and predator searching were important under some conditions. Factors of moderate importance were the adult female predator's functional response, total prey oviposition, the mode of the prey's oviposition curve, abiotic mortality of the pre-adult predator, and the effect of prey consumption on predator development and on the immature predator's mortality. Factors of least importance were the variances of the predator's and prey's oviposition curves, the abiotic mortality of the adult predator, the abiotic mortality of the pre-adult and adult prey, the functional response of the nymphal and adult male predators, and the effect of prey consumption on adult predator mortality. The sex ratios had little effect, except when the proportion of female predators was very low. The initial predator-prey ratio and time of predator introduction had significant impacts on system behavior, though the patterns of impact were different.     

Vacation farms and ecotourism in Saskatchewan, Canada

Vacation farms represent an increasingly significant rural diversification option for chronically unstable agriculture-based economies such as Saskatchewan. Concurrently, ecotourism is a rapidly expanding form of tourism which could serve to enhance the recreation product of such rural enterprises. Accordingly, a self-administered questionnaire was sent to all listed vacation farm operators in the province to obtain information on the provision of ecotourism opportunities. Just over one-half (n = 40) of all operations returned a completed questionnaire. Of 23 listed recreation options, wildlife viewing was cited as the activity most frequently undertaken by vacation farm visitors, followed by hunting, casual photography and touring. Wildlife viewing occurred most commonly during the spring and summer, with access to the resource occurring mainly on foot, and less so by horse and vehicle. Birds were the most important category of wildlife viewed, followed by mammals and plants; reptiles/amphibians, insects and fish were of only minor significance. It was evident that the sampled vacation farm operators possessed very little training in the area of ecotourism; few barriers or opportunities related to the latter were indicated. Appropriate recommendations include the provision of ecotourism training opportunities, stronger linkages between vacation farms and public spaces, and further investigation into the relationship between wildlife viewing and hunting activities.     

The Evolution of Organizations: Suggestions from Complexity Theory About the Interplay Between Natural Selection and Adaptation

There has been much debate in the managementliterature between neo-Darwinists (who believe in thenatural selection of populations of organizations) andadaptationists (who contend that changes in organization structure and behavior occur in response to theenvironment). The general thesis of neo-Darwinism isthat species are blindly selected for survival by theenvironment. The latest empirical support for the dominant neo-Darwinism perspective adopted bymost biologists is based primarily on the experimentsconducted by Salvador Luria who claims to haveconclusively demonstrated that genes mutate randomly.Recently, however, biologists have re-examined Luria sresearch methods and, after replications of hisexperiments, now question some aspects of the validityof his results. Moreover, there is now new researchwhich provides support for the earlier adaptationistposition, namely, the existence of evolutionary driversand directors existing within self-organizing systems.Of particular importance to the present study is the experimental indication thatself-organizing systems play a conscious role in theirown evolution. We propose that similar mechanisms orprocesses operate in organizational adaptation, thuspointing toward a theoretical modification ofneo-Darwinism that embraces both adaptation and naturalselection in a general, unified theory.     

Changes in Income Concentration: Taxes or Macroeconomic Conditions?

We examine the relative importance of tax rates and macroeconomic fluctuations in explaining the share of national adjusted gross income (AGI) reported by the top 0.5% of all taxpayers. Results indicate that cutting the top income or capital gains tax rate would increase the top AGI share but not by enough to increase revenues. The preponderance of evidence suggests that the top AGI share is affected more by the capital gains tax rate than by the income tax rate but that real gross domestic product fluctuations have even larger effects.     

ECONOMIC GLOBALIZATION AND WOMEN'S STATUS IN THE LABOR MARKET:

This study examines the effects of economic globalization on occupational sex segregation and occupational inequality. A theory of global economic restructuring and its impact on the quality of women's work suggests that national integration into the world economy significantly expands opportunities for women in the workplace but does not remove barriers to women's advancement or ameliorate the predominance of low-paying, menial jobs held by women. Two measures of gender occupational differentiation are employed as dependent variables in cross-sectional OLS regression analyses of fifty-six countries using data from 1970–1990. Results indicate that global economic forces reduce occupational sex segregation and inequality. However, these effects are determined by a country's world system position and region. The analyses illustrate that global economic restructuring is a gendered process that transforms and builds upon existing gender inequalities. Therefore, the inclusion of global structural characteristics into comparative research on occupational sex differentiation is essential.     

I'm OK, You're (Not) OK: The Private Welfare State in the United States

The American welfare state has been premised on the mixture of substantial private, tax‐subsidized benefits rather than on more universalistic public benefits. That pattern is in some ways being undermined as private pension plans are increasingly going bankrupt and firms reduce the benefits they provide employees. On the other hand, however, the current Bush administration is attempting to enhance the private sector role by allowing individuals to invest at least a part of their social insurance contributions into private savings plans. These changes may in the end increase the role of the public sector as a regulator and underwriter at the same time that attempts are made to minimize public sector involvement.     

Bayesian palaeoclimate reconstruction

Summary.  We consider the problem of reconstructing prehistoric climates by using fossil data that have been extracted from lake sediment cores. Such reconstructions promise to provide one of the few ways to validate modern models of climate change. A hierarchical Bayesian modelling approach is presented and its use, inversely, is demonstrated in a relatively small but statistically challenging exercise: the reconstruction of prehistoric climate at Glendalough in Ireland from fossil pollen. This computationally intensive method extends current approaches by explicitly modelling uncertainty and reconstructing entire climate histories. The statistical issues that are raised relate to the use of compositional data (pollen) with covariates (climate) which are available at many modern sites but are missing for the fossil data. The compositional data arise as mixtures and the missing covariates have a temporal structure. Novel aspects of the analysis include a spatial process model for compositional data, local modelling of lattice data, the use, as a prior, of a random walk with long-tailed increments, a two-stage implementation of the Markov chain Monte Carlo approach and a fast approximate procedure for cross-validation in inverse problems. We present some details, contrasting its reconstructions with those which have been generated by a method in use in the palaeoclimatology literature. We suggest that the method provides a basis for resolving important challenging issues in palaeoclimate research. We draw attention to several challenging statistical issues that need to be overcome.     

Bandwidth-based nonparametric inference

Nonparametric curve estimation is an extremely common statistical procedure. While its primary purpose has been exploratory, some advances in inference have been made. This paper provides a critical review of inferential tests that make fundamental use of a key element of nonparametric smoothing, the bandwidth, to determine the significance of certain features. A major focus is on two important problems that have been tackled using bandwidth-based inference: testing for the multimodality of a density and testing for the monotonicity of a regression curve. Early research in bandwidth-based inference is surveyed, as well as recent theoretical advances. Possible future directions in bandwidth-based inference are discussed.     

The Effects of a Creative Dance and Movement Program on the Social Competence of Head Start Preschoolers

The effects of an eight‐week instructional program in creative dance/movement on the social competence of low‐income preschool children were assessed in this study utilizing a scientifically rigorous design. Forty preschool children from a large Head Start program were randomly assigned to participate in either an experimental dance program or an attention control group. Teachers and parents, blind to the children's group membership, rated children's social competence both before and after the program, using English and Spanish versions of the Social Competence Behavior Evaluation: Preschool Edition. The results revealed significantly greater positive gains over time in the children's social competence and both internalizing and externalizing behavior problems for the experimental group compared with the control group. Small‐group creative dance instruction for at‐risk preschoolers appears to be an excellent mechanism for enhancing social competence and improving behavior. The implications for early childhood education and intervention are discussed.