Modelling the Optimal Strategies of Fertiliser Application Using the Game-Theoretic Approach

This paper is a case study which describes the application of game-theoretic approach in resource management with specific emphasis on developing optimal strategies of phosphorus applications for soil fertilisation. The approach adopted allows resource managers to consider not only competitive strategies, which were treated as the Nash equilibrium game solutions, but also strategies which imply cooperation between farmers. These strategies were modelled as the cooperative Pareto optima of the game. The objective function of the game has been developed in order to reflect both economic advantages of phosphorus applications and the environmental losses associated with these applications expressed as dollar values. The paper presents algorithms for finding competitive and cooperative solutions of the game for the particular case when no time scheduling is included in the game parametrisation. The results obtained in the paper showed that the cooperative solutions lead to much lesser environmental impacts than that in the case of non-cooperative strategies.     

Fate of large-scale vortices in idealized tidal lagoons

Environmental Fluid Mechanics - The generation and evolution of tidally-induced vortices in coastal and estuarine regions can influence water quality and sedimentary processes. These effects must...     

How many color metrics do we need? Evaluating how different color-scoring procedures explain carotenoid pigment content in avian bare-part and plumage ornaments

For a variety of technical and conceptual reasons, biologists have come to use several different methods to quantify the colors of animals. However, the relative abilities of these different color-scoring procedures to capture variation in the actual color-generating mechanisms—pigment or structural composition of the integument—have never been tested systematically. Here, we examined which commonly employed color metrics predict carotenoid content of ornaments in three avian species (house finch Carpodacus mexicanus, mallard duck Anas platyrhynchos, and zebra finch Taeniopygia guttata). We used spectrophotometry to measure reflectance spectra from beak and feather tissue, calculated numerous color metrics (e.g., hue, chroma, brightness, principal components, and tetrahedral color space position) from these spectra, and determined carotenoid content at the site of color measurement with high-performance liquid chromatography. We found that several principal component, tristimulus, and avian visual model metrics significantly correlated with carotenoid content of house finch feathers and duck beaks. Carotenoid content of mallard beaks was most closely correlated with brightness and saturation metrics, whereas in house finch feathers, carotenoid concentration was best captured by hue and saturation metrics. According to tristimulus scores and visual models, we found that the ultraviolet portion of the spectrum was not an essential predictor of variation in carotenoid content. Also, visual model chromatic contrasts generally were not significant predictors of carotenoid content, although some achromatic contrasts and tetrahedral color space vector parameters were. Our results indicate that numerous methods, especially tristimulus scores, are suitable for capturing pigment-based color variation in two carotenoid-containing ornaments, and we discuss the merits and shortcomings of these different approaches. In contrast, there were no significant relationships between any color metrics and the carotenoid content of zebra finch beaks, suggesting that other color-generating mechanisms besides carotenoids may contribute to color variability in this species.     

Seaweed diversity enhances nitrogen uptake via complementary use of nitrate and ammonium

The consequences of declining biodiversity remain controversial, in part because many studies focus on a single metric of ecosystem functioning and fail to consider diversity's integrated effects on multiple ecosystem functions. We used tide pool microcosms as a model system to show that different conclusions about the potential effects of producer diversity on ecosystem functioning may result when ecosystem functions are measured separately vs. together. Specifically, we found that in diverse seaweed assemblages, uptake of either nitrate or ammonium alone was equal to the average of the component monocultures. However, when nitrate and ammonium were available simultaneously, uptake by diverse assemblages was 22% greater than the monoculture average because different species were complementary in their use of different nitrogen forms. Our results suggest that when individual species have dominant effects on particular ecosystem processes (i.e., the sampling effect), multivariate complementarity can arise if different species dominate different processes. Further, these results suggest that similar mechanisms (complementary nutrient uptake) may underlie diversity-functioning relationships in both algal and vascular-plant-based systems.     

Hydrogen sulfide generation in simulated construction and demolition debris landfills: impact of waste composition

Hydrogen sulfide (H2S) generation in construction and demolition (C&D) debris landfills has been associated with the biodegradation of gypsum drywall. Laboratory research was conducted to observe H2S generation when drywall was codisposed with different C&D debris constituents. Two experiments were conducted using simulated landfill columns. Experiment 1 consisted of various combinations of drywall, wood, and concrete to determine the impact of different waste constituents and combinations on H2S generation. Experiment 2 was designed to examine the effect of concrete on H2S generation and migration. The results indicate that decaying drywall, even alone, leached enough sulfate ions and organic matter for sulfate-reducing bacteria (SRB) to generate large H2S concentrations as high as 63,000 ppmv. The codisposed wastes show some effect on H2S generation. At the end of experiment 1, the wood/drywall and drywall alone columns possessed H2S concentrations > 40,000 ppmv. Conversely, H2S concentrations were < 1 ppmv in those columns containing concrete. Concrete plays a role in decreasing H2S by increasing pH out of the range for SRB growth and by reacting with H2S. This study also showed that wood lowered H2S concentrations initially by decreasing leachate pH values. Based on the results, two possible control mechanisms to mitigate H2S generation in C&D debris landfills are suggested.     

Glues or poisons: which triggers vein cutting by monarch caterpillars?

Summary. Late instar larvae of the monarch butterfly (Danaus plexippus L., Lepidoptera: Nymphalidae) deactivate the latex defense of milkweeds by chewing a furrow in the leaf midrib or petiole. The larva then feeds beyond the cut where latex outflow is minimal. If a larva does encounter latex exudate during feeding, it often returns to its initial cut to damage the midrib or petiole more extensively before resuming feeding. We used this response to latex as an assay for testing what cue triggers vein cutting. A sticky solution of polyethylene glycol and a mixture of cardenolides both were ineffective; drops applied to the mouthparts of feeding monarchs failed to elicit renewed vein cutting. Activity resided instead within a methanol extract of the supernatant obtained from centrifuged latex of the milkweed, Asclepias curassavica L. (Asclepiadaceae). Treatment with proteinase K did not eliminate activity documenting that the active compound is unlikely to be proteinaceous. Our results indicate that latex adhesiveness and low polarity cardenolides are relatively unimportant releasers of vein cutting. We propose that milkweeds contain noncardenolide stimulants of vein cutting; these compounds presumably serve a defensive role for milkweeds. Over 50 species of insects are known to employ vein-cutting before feeding on plants with canal-borne exudates; most of these species are dietary specialists like the monarch. Our behavioral assay provides a novel approach for identifying ecologically-significant compounds in the exudates of their diverse host plants.