Predators choosing between patches with standing crop: the influence of switching rules and input types

Where prey arriving in a patch are not consumed immediately, they will accumulate. Predators are then presented with a prey density or standing crop that increases through further input, and decreases through the consumption by predators. Firstly, I show that the switching rule of predators has a significant influence on the expected predator equilibrium distribution in such a dynamic system. Three rules are compared; for all rules, analytical solutions are calculated (where possible). To test their plausibility for natural situations, predator distributions are simulated given the assumption that each predator obtains individual patch profitability estimates by using a common learning rule. As long as prey arrive in the patches in constant numbers per time unit, the first rule leads to input matching because predators stop switching when consumption in the two patches is equal. The other two rules, where predators continue to sample both patches even in the equilibrium state, lead to predator distributions where the more profitable patch is underused. The final equilibrium depends on the exact assumptions of the switching rule; however, it is independent of interference. But if the input delivered into a patch is a function of the current prey standing crop (for example in a reproducing prey population), predator and prey distributions will not reach an equilibrium in most cases: either standing crops increase indefinitely, or they approach zero, with all predators concentrating on the better patch. Only a small number of parameter sets show intermediate crops that are reasonably stable. With this input type, only up to 54% of the simulations reach the expected distribution. In a system with competition for dynamic standing crop, it is therefore essential to know the type of input and the switching-rule used by predators to be able to predict equilibrium predator distributions. Received: 17 March 1995/Accepted after revision: 5 November 1995     

A free lunch in the commons

We derive conditions under which raising costs through a regulatory constraint or a fully expropriated tax can increase the profits arising from a common-pool resource. The basic model assumes a fixed number of identical agents with linear costs selling in a single period at an exogenous price. A necessary and sufficient condition for a cost increase to be profitable is that aggregate output from the resource be locally convex in aggregate effort. We also show that cost increases can be profitable even if price is endogenous, agents are heterogeneous, entry is costless, or agents are playing a Markov-perfect equilibrium of a dynamic game. We also discuss more general welfare implications of the result along with its relation to existing results for a Cournot oligopoly.     

High adsorption of dyes by water hyacinth fixed on alginate

Pollution from synthetic dyes has emerged to be a significant environmental issue over the past few decades. This has mainly been triggered by the increasing global dye production, possible toxic effects, undesirable colour and high persistence in the environment. Biosorption, which involves dye removal from aqueous solution by passive linkage in live and dead biomass, has shown great potential in removing dyes from aquatic environments. Among aquatic macrophytes, water hyacinth, Eichhornia crassipes, has shown great potential as a biosorbent. In this work, we investigated the removal of two basic dyes, methylene blue and crystal violet, using E. crassipes immobilized on alginate. Results showed that the Langmuir model better described the equilibrium sorption data when compared to the Freundlich model. Optimum amounts of methylene blue and crystal violet dyes were adsorbed in the alkaline pH range (8–10), 8 % biomass dose, and the amount of dye removed increased with increasing initial dye concentration. The equilibrium monocomponent adsorption capacities for the dyes were 111.1 and 43.5 mg/g, while the binary adsorption capacities were 26.1 and 11.6 mg/g for methylene blue and crystal violet, respectively. To conclude, we show for the first time that E. crassipes fixed on alginate beads can uptake and adsorb methylene blue and crystal violet dyes very effectively in batch systems and show great potential for dye removal from aquatic environments.     

Role of competition in phytoplankton population for the occurrence and control of plankton bloom in the presence of environmental fluctuations

Termination of harmful algal blooms (HABs) and coexistence of phytoplankton–zooplankton populations are of great importance to human health, ecosystem, environment, tourism and fisheries. In this paper, we propose a three component model consisting of non-toxic phytoplankton (NTP), toxin producing phytoplankton (TPP) and zooplankton (Z). The growth of zooplankton species is assume to reduce due to toxic chemicals released by TPP population. We have extended the model proposed by Chattopadhyay et al. [Chattopadhyay, J., Sarkar, R.R., Pal, S., 2004. Mathematical modelling of harmful algal blooms supported by experimental findings. Ecol. Comp. 1, 225–235] by including competition terms between TPP and NTP. We observe the effect of competition factors both in the presence and absence of the environmental fluctuation. From our field as well as model analysis we observe that competition helps in the coexistence of the species, but if the effect of competition is very high on the TPP population, it results in planktonic bloom. It is shown that the coexistence equilibrium loses its stability when the competition coefficient crosses a critical value and resulting Hopf-bifurcation around the positive equilibrium depicting oscillations phenomena of the populations.     

关于有序填海的思路与方法

填海造陆在扩展土地和发展经济的同时也对海岸带环境造成了不利影响。将有序人类活动贯穿于整个填海造陆过程,通过科学合理的规划、组织和实施而进行有序填海,从而增加填海造陆的积极效应,限制其破坏性影响,是实现海岸带可持续发展的必由之路。整体性、矛盾论、动态平衡和因地制宜是有序填海的基本观点。要实现有序填海,首先必须在对填海造陆的效益和损失进行科学评价的基础上进行可行性论证,然后制定不同尺度的填海规划并确定填海造陆的适宜规模,最后利用一系列有效方法加以实施,包括：维护海岸带自然系统功能、完善监督管理制度、实行生态补偿与生态系统重建、加速改良填海区环境等。     

Feasibility and stability in randomly assembled Lotka-Volterra models

For a Lotka-Volterra model to represent a viable ecosystem it's nontrivial equilibrium must be feasible. If m is the number of species, it is shown that in a set of randomly assembled Lotka-Volterra models, the fraction of models with a feasible equilibrium is some function of m which behaves like 2^?m. Moreover a subset of Lotka-Volterra models, each of which has a feasible equilibrium, has the same stability property as a set of linear models which is assembled randomly in the same manner. This contradicts a recent claim that a Lotka-Volterra model with a feasible equilibrium tends to be stable. Thus for two reasons the probability that a Lotka-Volterra model represents a viable and stable ecosystem decreases rapidly with the number of species. This supports the theme developed by May that stability in model ecosystems decreases with diversity.     

Modelling the distribution and effect of heavy metals in an aquatic ecosystem

Models are reviewed describing the distribution and effect of heavy metals in an aquatic ecosystem. Since a model used for an impact statement should give the maximum concentration level rather than the seasonal variation, a model focussing on this situation is suggested. The basic differential equations describe (1) the variation in concentration of the toxicant per biomass dry matter in a given trophic level, and (2) the exchange of toxicant between sediment and water. Furthermore, since a substantial part of the heavy metal in an aquatic ecosystem is bound to suspended matter, an equation describing the equilibrium between dissolved and suspended matter must be included.A literature review has been carried out on the parameters used in the above mentioned equations and a demonstration, showing how it is possible to find approximate values for such parameters as excretion coefficient and uptake coefficient on the basis of a relationship between these two parameters and the size of an organism, is given.     

The response of the woodpigeon (Columba palumbus) to relaxation of intraspecific competition: A hybrid modelling approach

The recent rapid growth of the woodpigeon population in the British Isles is a cause for concern for environmental managers. It is unclear what has driven their increase in abundance. Using a mathematical model, we explored two possible mechanisms, reduced intraspecific competition for food and increased reproductive success. We developed an age-structured hybrid model consisting of a system of ordinary differential equations that describes density-dependent mortality and a discrete component, which represents the birth-pulse. We investigated equilibrium population dynamics using our model. The two hypotheses predict contrasting population age profiles at equilibrium. We adapted the model to examine the impacts of control measures. We showed that an annual shooting season that follows the period of density-dependent mortality is the most effective control strategy because it simultaneously removes adult and juvenile woodpigeons. The model is a first step towards understanding the processes that influence the dynamics of woodpigeon populations.     

Valuing nature in a general equilibrium

We explore the consequences of modeling the demand for environmental quality improvements as a fully integrated part of a general equilibrium demand system in an applied general equilibrium (or CGE) analysis. Demand for non-market goods depends on a full range of relative prices as well as environmental outcomes. We simulate the effects of reducing two air pollutants to improve human health and three ecosystem services provided to households. The ecosystem services make non-separable contributions to household utility. We find that willingness to pay measures of use-based ecosystem services are impacted by changes in demand for complementary market goods. Demand for these goods shifts due to pollution reductions that enhance ecosystem services. Partial equilibrium estimates of these use values can be measured with substantial error if they fail to account for the general equilibrium adjustments caused by pollution. Over 300 calibrations of the model identify the model features important to these errors. We find that effects on ecosystem services associated with non-use values have important implications for the feedback effects on use related measures of economic tradeoffs. This is due to how our model integrates market and non-market effects, reflecting the non-market services importance to general equilibrium market outcomes.     

The case for international emission trade in the absence of cooperative climate policy

We evaluate the efficacy of international trade in carbon emission permits when countries are guided strictly by their national self-interest. To do so, we construct a calibrated general equilibrium model that jointly describes the world economy and the strategic incentives that guide the design of national abatement policies. Countries’ decisions about their participation in a trading system and about their initial permit endowment are made non-cooperatively; so a priori it is not clear that permit trade will induce participation in international abatement agreements or that participation will result in significant environmental gains. Despite this, we find that emission trade agreements can be effective; that smaller groupings pairing developing and developed-world partners often perform better than agreements with larger rosters; and that general equilibrium responses play an important role in shaping these outcomes.     

The case for international emission trade in the absence of cooperative climate policy

We evaluate the efficacy of international trade in carbon emission permits when countries are guided strictly by their national self-interest. To do so, we construct a calibrated general equilibrium model that jointly describes the world economy and the strategic incentives that guide the design of national abatement policies. Countries’ decisions about their participation in a trading system and about their initial permit endowment are made non-cooperatively; so a priori it is not clear that permit trade will induce participation in international abatement agreements or that participation will result in significant environmental gains. Despite this, we find that emission trade agreements can be effective; that smaller groupings pairing developing and developed-world partners often perform better than agreements with larger rosters; and that general equilibrium responses play an important role in shaping these outcomes.     

On equilibrium in resource markets with scale economies and stochastic prices

In this paper, I show the existence and the characteristics of equilibrium in a non-renewable resource market where extraction costs are non-convex and market price is subject to stochastic shocks, an empirically relevant setting. In my model firms may be motivated to hold inventories to facilitate production smoothing, which allows them to continue producing at a smooth pace at any instant when extraction ceases, e.g. when reserves are exhausted. This aspect of the model then supports a competitive equilibrium in the presence of non-convex costs. Casual empirical evidence is provided that supports the central features of my model for a variety of non-renewable resources, lending credence to the explanation for equilibrium I propose.     

On equilibrium in resource markets with scale economies and stochastic prices

In this paper, I show the existence and the characteristics of equilibrium in a non-renewable resource market where extraction costs are non-convex and market price is subject to stochastic shocks, an empirically relevant setting. In my model firms may be motivated to hold inventories to facilitate production smoothing, which allows them to continue producing at a smooth pace at any instant when extraction ceases, e.g. when reserves are exhausted. This aspect of the model then supports a competitive equilibrium in the presence of non-convex costs. Casual empirical evidence is provided that supports the central features of my model for a variety of non-renewable resources, lending credence to the explanation for equilibrium I propose.     

Removal of Methylene Blue from aqueous solution by marine green alga Ulva lactuca

Biosorption of colours is an important technology for treatment of different types of industrial wastewaters containing dyes. The objective of this study was to convert green alga Ulva lactuca to dye adsorbents for wastewater treatment. The importance of commonly available green alga Ulva lactuca was investigated as viable biomaterials for the biological treatment of synthetic basic blue 9 (5-ch1oro-N,N,N^',N^'-tetramethyl-5λ⁴-phenothiazine-3,7-diamine) effluents. The results obtained from the batch experiments revealed the ability of the green algae to remove the basic blue 9, and this was dependent on the dye concentration, pH, and algal biomass. We investigated the equilibrium and kinetics of adsorption, and the Langmuir and Freundlich equations were used to fit the equilibrium isotherm. The adsorption isotherm of basic blue 9 followed both the Langmuir and Freundlich models with a correlation coefficient of ∼0.96-0.99, and the adsorption kinetics followed the pseudo-second-order model (R²=1.0). The maximum adsorption capacity was about 40.2 mg of dye per gram of dry green algae at pH 10, 25 g l^-1 dye and 2.5 g l^-1 alga concentrations. This study demonstrated that the green algae could be used as an effective biosorbent for the treatment of dye-containing wastewater streams.     

Task selection by workers of the fire ant Solenopsis invicta

The effects of worker size, age, and crop fullness on the flow of food into the colony were assessed using video recording and playback. Regardless of the level of colony satiation, small workers seldom had full crops and were more involved in larval grooming than in food traffic. Large workers played little role in larval care, but tended to be recruited easily to a food source and to store food in their crops. Medium workers had crops ranging from empty to full because they alternated between ingesting from and donating food to other colony members. Medium workers were the most versatile, engaging competently in food recruitment, larval grooming, and larval feeding. They displayed considerable variation in the frequency at which they fed larvae: some fed a few larvae before switching to other tasks, others fed over a hundred larvae before switching. The persistence, or lack thereof, of a worker's feeding response suggests a flexibility unaccounted for by the fixed-threshold-response hypothesis. Worker coverage of the brood pile was a dynamic equilibrium process unaffected by worker size, age, or crop fullness, or by differences in the nutritional or hygienic states of larvae. In summary, it appeared that worker size and age offered coarse regulation of task selection by workers, whereas crop fullness, flexible response, and task switching fine-tuned task selection. Received: 25 May 1998 / Accepted after revision: 20 August 1998     

Migration effects in a stochastic multipopulation model for African bee population dynamics

The rate of northern migration of the Africanized honey bee (AHB) in the United States has recently slowed dramatically. This paper investigates the impact of migration on the equilibrium size distributions of a particular stochastic multipopulation model, namely a coupled logistic power law model. The bivariate equilibrium size distribution of the model is derived and illustrated with parameter values used to describe AHB population dynamics. In the model, the difference between the equilibrium sizes of the two populations is a measure of the effect of migration. The distribution of this difference may be approximated by a normal distribution. The mean and variance parameters for the normal are predicted accurately by a second-order regression model based on the migration rate and the maximum size of the first population. The methodology is general, and should be useful in studying the migration effect in many other applications with one-way migration.     

Model selection and model averaging in behavioural ecology: the utility of the IT-AIC framework

Behavioural ecologists often study complex systems in which multiple hypotheses could be proposed to explain observed phenomena. For some systems, simple controlled experiments can be employed to reveal part of the complexity; often, however, observational studies that incorporate a multitude of causal factors may be the only (or preferred) avenue of study. We assess the value of recently advocated approaches to inference in both contexts. Specifically, we examine the use of information theoretic (IT) model selection using Akaike’s information criterion (AIC). We find that, for simple analyses, the advantages of switching to an IT-AIC approach are likely to be slight, especially given recent emphasis on biological rather than statistical significance. By contrast, the model selection approach embodied by IT approaches offers significant advantages when applied to problems of more complex causality. Model averaging is an intuitively appealing extension to model selection. However, we were unable to demonstrate consistent improvements in prediction accuracy when using model averaging with IT-AIC; our equivocal results suggest that more research is needed on its utility. We illustrate our arguments with worked examples from behavioural experiments.     

鸟粪石法沉淀去除氨氮的平衡体系模拟预测

使用化学平衡软件Visual MINTEQ计算拟合鸟粪石(磷酸镁铵,MgNH4PO4·6H2O,MAP)沉淀去除氨氮的平衡体系在不同pH值条件下Mg2+、NH4+和PO34-各组分的变化及饱和指数(SI)的变化.实验和预测结果表明,模型对MAP沉淀平衡体系拟合良好.在本研究的pH值范围内(8.0—11.0),化学平衡模型VisualMINTEQ能预测敞开体系氨氮废水中通过磷酸铵镁沉淀去除的NH4+-N,但不能用来预测敞开体系中所有氨氮的去除,即预测结果中不包括由于氨气挥发而去除的氨氮.     

Response of balanced network models to large-scale perturbation: Implications for evaluating the role of small pelagics in the Gulf of Maine

Exploring the response of an ecosystem, and subsequent tradeoffs among its biological community, to human perturbations remains a key challenge for the implementation of an ecosystem approaches to fisheries (EAF). To address this and related issues, we developed two network (or energy budget) models, Ecopath and Econetwrk, for the Gulf of Maine ecosystem. These models included 31 network “nodes” or biomass state variables across a broad range of trophic levels, with the present emphasis to particularly elucidate the role of small pelagics. After initial network balancing, various perturbation scenarios were evaluated to explore how potential changes to different fish, fisheries and lower trophic levels can affect model outputs. Categorically across all scenarios and interpretations thereof, there was minimal change at the second trophic levels and most of the “rebalancing” after a perturbation occurred via alteration of the diet matrix. Yet the model results from perturbations to a balanced energy budget fall into one of three categories. First, some model results were intuitive and in obvious agreement with established ecological and fishing theory. Second, some model results were counter-intuitive upon initial observation, seemingly contradictory to known ecological and fishing theory; but upon further examination the results were explainable given the constraints of an equilibrium energy budget. Finally, some results were counter-intuitive and difficult to reconcile with theory or further examination of equilibrium constraints. A detailed accounting of biomass flows for example scenarios explores some of the non-intuitive results more rigorously. Collectively these results imply a need to carefully track biomass flows and results of any given perturbation and to critically evaluate the conditions under which a new equilibrium is obtained for these types of models, which has implications for dynamic simulations based off of them. Given these caveats, the role of small pelagics as a prominent component of this ecosystem remains a robust conclusion. We discuss how one might use this approach in the context of further developing an EAF, recognizing that a more holistic, integrated perspective will be required as we continue to evaluate tradeoffs among marine biological communities.