Quantifying migratory capacity and dispersal of the invasive Tench (Tinca tinca) in the St. Lawrence River using otolith chemistry

The study of distribution and dispersal of invasive fishes is challenging during the early stages of invasion. Quantification of trace elements incorporated into fish hard parts represents an innovative technique for this task. Otolith chemistry has been used to describe fish stock structure, migratory behaviour and to support the management of several species. We used otolith chemistry to study the dispersal and population structure of Tench (Tinca tinca), an invader in the St Lawrence River. Tench movements throughout the invaded portion of the system were reconstructed using a Random Forests Algorithm. The results showed that, despite the presumed limited dispersal capacity of the species, Tench are capable of extensive migratory movements (up to 250 km). The variability in migratory patterns among individuals, including both short- and long-distance movements, supports a stratified diffusion. Such a strategy may explain the successful invasion of Tench in the St Lawrence River ecosystem. Our study represent a flexible framework for the study of Tench ecology in its invaded and native range, as well as for other freshwater invasive fishes.

Scale invariance in the spatial-dynamics of biological invasions

Despite the enormous negative consequences of biological invasions, we have a limited understanding of how spatial demography during invasions creates population patterns observed at different spatial scales. Early stages of invasions, arrival and establishment, are considered distinct from the later stage of spread, but the processes of population growth and dispersal underlie all invasion phases. Here, we argue that the spread of invading species, to a first approximation, exhibits scale invariant spatial-dynamic patterns that transcend multiple spatial scales. Dispersal from a source population creates smaller satellite colonies, which in turn act as sources for secondary invasions; the scale invariant pattern of coalescing colonies can be seen at multiple scales. This self-similar pattern is referred to as “stratified diffusion” at landscape scales and the “bridgehead effect” at the global scale. The extent to which invasions exhibit such scale-invariant spatial dynamics may be limited by the form of the organisms’ dispersal kernel and by the connectivity of the habitat. Recognition of this self-similar pattern suggests that certain concepts for understanding and managing invasions might be widely transferable across spatial scales.

Study of the transport modeling by diffusion of pollutants through porous materials

This paper presents how distance function dispersal produces diffusion range expansion of the contamination. We construct a stratified diffusion model, which describes the dynamics of the size distribution of colonies created by distance migrants of metal ions. The model consists of a Fick's equation combined with a Navier-stokes. The model provides an estimate of range expansion in terms of the rate adsorption due to neighborhood diffusion, the leap time and the geometric form. The results explain various types of nonlinear range expansion observed in materials or biomaterials.

Quantifying spatio-temporal variation of invasion spread

— The spread of invasive species can have far-reaching environmental and ecological consequences. Understanding invasion spread patterns and the underlying process driving invasions are key to predicting and managing invasions. — We combine a set of statistical methods in a novel way to characterize local spread properties and demonstrate their application using simulated and historical data on invasive insects. Our method uses a Gaussian process fit to the surface of waiting times to invasion in order to characterize the vector field of spread. — Using this method, we estimate with statistical uncertainties the speed and direction of spread at each location. Simulations from a stratified diffusion model verify the accuracy of our method. — We show how we may link local rates of spread to environmental covariates for two case studies: the spread of the gypsy moth ( Lymantria dispar ), and hemlock woolly adelgid ( Adelges tsugae ) in North America. We provide an R-package that automates the calculations for any spatially referenced waiting time data.

Why Has the Critique of the Leisure Class Run out of Steam? Matters of Fact and Matters of Concern

The article analyzes the conceptual and historical prerequisites for the transition from the classical theory of leisure to modern leisure studies. Its central question is what “matters of fact” and “matters of concern” have had the greatest impact on the formation of the new research agenda. The first part of the article reconstructs Veblen’s conceptualization of the leisure class, which is associated with extensive free time, specific types of leisure, demonstrative consumption of the output from productive work, and the elevated socio-economic status that a particular group attains by following the conventions of a “prestigious” lifestyle. It is argued that the focus on stable, reproducible patterns of behavior in the upper class neglected the distinction between newer leisure practices, as well as the stratified diffusion of leisure time. The author describes three exogenous factors that have undercut the traditional understanding of leisure in the social sciences: the transformation of the temporal structure of work and leisure as a result of the broad penetration of digital technologies; the blurring of the boundaries between workspaces and recreational areas; and the transformation of the resources for economic interactions and of the system for conversion to various types of capital in the labor market. Changes in the basic criteria for a leisure lifestyle have exposed problems with Veblen’s intuitions and have led to the emergence of new disciplinary coalitions. In conclusion, the article deals with the problem of how to describe the modern leisure class. This is a question of whether the emergence of alternative leisure practices provides a sufficient basis for the identification of new leisure groups and of what would constitute a necessary condition for revamping the sociology of leisure.