Dispersion of particles released at the leading edge of a crop canopy

A large-eddy simulation (LES) approach was used to investigate the flow characteristics at a canopy leading edge and their impact on the dispersion of particles released from point sources inside the canopy. Comparison of results from these LES simulations with those for a canopy that is infinite and uniform in both streamwise and spanwise directions reveals important insights about the adjustment lengths for mean flow, turbulent kinetic energy (TKE), and canopy-shear-layer vortices. Two critical locations were identified in the flow adjustment at the leading edge: (1) the location at which canopy-shear-layer vortices begin to develop and (2) the location at which the flow is fully developed. Simulations were conducted for particles released from continuous point sources at four streamwise locations downwind from the leading edge and three heights within the canopy. The four streamwise source locations corresponded to the canopy leading edge, the location at which canopy-shear-layer vortices began to develop, the transition region, and the fully developed region. The adjustment of flow near the leading edge has a profound impact on the dispersion of particles close to the source, which is where most particle escape from the canopy takes place. Particles released close to the canopy leading edge have much higher maximum escape fractions than particles released in the fully developed region. The adjustment length for particle escape is greater than that for the flow. Away from the source (approximately sixteen canopy heights for the present dense canopy), the geometries of the mean plume become similar for particles released from different regions. Within a few tens of canopy heights from the leading edge, the growth rates of converged mean plume height and depth are lower than those for the case of an infinite canopy.National Science Foundation (U.S.) (Grant AGS1005363

Identifying Highly Connected Counties Compensates for Resource Limitations when Evaluating National Spread of an Invasive Pathogen

Surveying invasive species can be highly resource intensive, yet near-real-time evaluations of invasion progress are important resources for management planning. In the case of the soybean rust invasion of the United States, a linked monitoring, prediction, and communication network saved U.S. soybean growers approximately $200 M/yr. Modeling of future movement of the pathogen (Phakopsora pachyrhizi) was based on data about current disease locations from an extensive network of sentinel plots. We developed a dynamic network model for U.S. soybean rust epidemics, with counties as nodes and link weights a function of host hectarage and wind speed and direction. We used the network model to compare four strategies for selecting an optimal subset of sentinel plots, listed here in order of increasing performance: random selection, zonal selection (based on more heavily weighting regions nearer the south, where the pathogen overwinters), frequency-based selection (based on how frequently the county had been infected in the past), and frequency-based selection weighted by the node strength of the sentinel plot in the network model. When dynamic network properties such as node strength are characterized for invasive species, this information can be used to reduce the resources necessary to survey and predict invasion progress

From Select Agent to an Established Pathogen: The Response to \u3ci\u3ePhakopsora pachyrhizi\u3c/i\u3e (Soybean Rust) in North America

The pathogen causing soybean rust, Phakopsora pachyrhizi, was first described in Japan in 1902. The disease was important in the Eastern Hemisphere for many decades before the fungus was reported in Hawaii in 1994, which was followed by reports from countries in Africa and South America. In 2004, P. pachyrhizi was confirmed in Louisiana, making it the first report in the continental United States. Based on yield losses from countries in Asia, Africa, and South America, it was clear that this pathogen could have a major economic impact on the yield of 30 million ha of soybean in the United States. The response by agencies within the United States Department of Agriculture, industry, soybean check-off boards, and universities was immediate and complex. The impacts of some of these activities are detailed in this review. The net result has been that the once dreaded disease, which caused substantial losses in other parts of the world, is now better understood and effectively managed in the United States. The disease continues to be monitored yearly for changes in spatial and temporal distribution so that soybean growers can continue to benefit by knowing where soybean rust is occurring during the growing season

A Unifying Gravity Framework for Dispersal

Most organisms disperse at some life-history stage, but different research traditions to study dispersal have evolved in botany, zoology, and epidemiology. In this paper, we synthesize concepts, principles, patterns, and processes in dispersal across organisms. We suggest a consistent conceptual framework for dispersal, which utilizes generalized gravity models. This framework will facilitate communication among research traditions, guide the development of dispersal models for theoretical and applied ecology, and enable common representation across taxonomic groups, encapsulating processes at the source and destination of movement, as well as during the intervening relocation process, while allowing each of these stages in the dispersal process to be addressed separately and in relevant detail. For different research traditions, certain parts of the dispersal process are less studied than others (e.g., seed release processes in plants and termination of dispersal in terrestrial and aquatic animals). The generalized gravity model can serve as a unifying framework for such processes, because it captures the general conceptual and formal components of any dispersal process, no matter what the relevant biological timescale involved. We illustrate the use of the framework with examples of passive (a plant), active (an animal), and vectored (a fungus) dispersal, and point out promising applications, including studies of dispersal mechanisms, total dispersal kernels, and spatial population dynamics

A Unifying Gravity Framework for Dispersal

Most organisms disperse at some life-history stage, but different research traditions to study dispersal have evolved in botany, zoology, and epidemiology. In this paper, we synthesize concepts, principles, patterns, and processes in dispersal across organisms. We suggest a consistent conceptual framework for dispersal, which utilizes generalized gravity models. This framework will facilitate communication among research traditions, guide the development of dispersal models for theoretical and applied ecology, and enable common representation across taxonomic groups, encapsulating processes at the source and destination of movement, as well as during the intervening relocation process, while allowing each of these stages in the dispersal process to be addressed separately and in relevant detail. For different research traditions, certain parts of the dispersal process are less studied than others (e.g., seed release processes in plants and termination of dispersal in terrestrial and aquatic animals). The generalized gravity model can serve as a unifying framework for such processes, because it captures the general conceptual and formal components of any dispersal process, no matter what the relevant biological timescale involved. We illustrate the use of the framework with examples of passive (a plant), active (an animal), and vectored (a fungus) dispersal, and point out promising applications, including studies of dispersal mechanisms, total dispersal kernels, and spatial population dynamics

Endogenous technological change, innovation diffusion and transitional dynamics in a nonlinear growth model

This paper addresses capital accumulation and capital productivity change in an economy with endogenous technological change and floors and ceilings in activity. The properties of the resulting two-variable nonlinear differential equation system are studied in some detail. The welfare implications are also considered. When discrete lags are introduced, wide-ranging behaviour emerges, which includes convergence to a steady-state, catastrophes, hysteresis, limit cycles and chaos. Simulations illustrate the results. It is found that external shocks, such as the diffusion of innovations from elsewhere, do not just change the level of the steady-state equilibrium but also the dynamical properties of the paths of output and productivity

Dispersal of Synanthropic Diptera: Lessons from the Past and Technology for the Future

The impact of aerial invasion of new habitats by dispersal of synanthropic arthropods on human society is one of the most important topics in the entomological world. A review is presented of important advances in the knowledge of dispersal of a number of dipteran species that cause damage to, or serve as vectors for diseases of, humans and associated animals. The components of aerial dispersal are delineated, and forms of dispersal are defined in the context of interactive forces that result in dispersal by synanthropic Diptera. Migratory flights by black flies are put into ecological perspective, as are the wind-borne movements of ceratopogonid vectors of viruses. Dispersal by house flies, screwworms, and stable flies are specifically addressed to trace the changes in technology used to detect and quantify aerial dispersal during the 20th century and to propose new ways to use current technology