2,794 research outputs found
Modeling the dynamics of tritrophic population interactions.
No full textIntroduction Increasingly, population modeling and systems analysis are being used to examine the complex issues that are at the heart of CP/IPM (crop production and integrated pest management) and biological control. The design of economically sound and sustainable crop management strategies requires a thorough understanding of the whole production system including arthropod pests, pathogens, and weeds. More than three decades ago, Huffaker and Croft (1976) stressed the need to rely on systems analysis and interdisciplinary collaboration to accomplish this task. Soon the question arose as to how mathematical techniques employed in the analysis of physical systems could be adapted to solve agroecosystem problems that are principally biological in nature and that focus on population management (Gutierrez and Wang, 1977; Getz and Gutierrez, 1982). Simple models of population dynamics often excluded the biological details for mathematical tractability and hence are frequently inadequate instruments for field application. Individual-based models have been used to explore population interactions (e.g. De Angelis and Gross, 1992), but often the rules for the interactions at the individual level are unknown. Simulation approaches stress biological realism and completeness and some show promise for exploring system structure and function, especially physiologically based models (PBM) (Gutierrez and Wang, 1977), sufficient to gain insights into complex quantitative relationships (see Gilbert et al., 1976; Gutierrez and Baumgärtner, 1984a; b; Graf et al., 1990a; Gutierrez, 1996; Di Cola et al., 1998). In this chapter we will consider only physiologically based multitrophic population dynamics models, or models with the potential to be so extended
Eco-social analysis of an East African agro-pastoral system : management of tsetse and trypanosomiasis
No full textA key constraint for development of many East African agro-pastoral communities is African animal trypanosomiasis or nagana caused by Trypanosoma spp. and vectored by species of tsetse flies (Glossina spp.). Suppression of trypanosomiasis through trapping of tsetse fly populations was conducted from 1995 to 2005 at and near Luke, Southwest Ethiopia. Odor baited mass trapping technology was used to suppress adult fly populations to very low levels while tryponocidal drugs were used to treat trypanosome infections in cattle. Data on ecological, economic and social variables were collected and analyzed in the context of eco-social dynamics in the community. The bio-economic model of Regev et al. [Regev, U., Gutierrez, A.P., Schreiber, S.J., Zilberman, D., 1998. Biological and Economic Foundations of Renewable Resource Exploitation. Ecological Economics 26, 227-242] and Gutierrez and Regev [Gutierrez, A.P., Regev, U., 2005. The bioeconomics of tritrophic systems: applications to invasive species. Ecological Economics 52, 382-396] was used as a methodological framework for qualitative evaluation of the effects of tsetse/trypanosomiasis suppression on ecological, economic and social aspects. An objective function for single farmers was formulated to determine the optimal harvesting level of cattle, exposed to high and low levels of risk from tsetse/trypanosomiasis, as measured by the discount rate (δ) for a given base level pastoral resource (R = pasture or forage for cattle). The socially optimal objective function for resource exploitation by all farmers is that which maximizes the present value of utility of individuals expending revenues (consumption) from the revenue stream in ways that enhance the quality of life and yet assures the persistence of the resource base over an infinite time horizon (i.e., renewable resource sustainability). The bio-economic model predicts that reducing risk (δ) from tsetse and disease increased the cattle populations and their marginal value. The model also predicts that the interaction of decreased δ and increased productivity (θ) can lead to increased human and cattle populations and hence to over-exploitation of base resources (pastures) that lower environmental carrying capacity and reduced sustainability. Trap catches indicated that tsetse populations were reduced to very low levels, while the disease prevalence decreased from 29% to 10%. This led to a substantial increase in cattle including oxen populations, increased calving rates, increased milk production and increased the per-capita income. The availability of oxen allowed an increase in cultivated land from 12 ha in 1995 to 506 ha in 2005. Revenues (consumption) were invested in the purchase of more cattle and the establishment of a school for educating village children. Increases in land allocated to crops and other sources of income were also found. The bioeconomic model predicts the solution of the trypanosomiasis problems so transforms the East African agro-pastoral communities that new social structures will be required to cope with the ecological, economic and social consequences of this technological changes on sustainable development (sensu [Goodland, R., 1995. The concept of environmental sustainability. Annual Review of Ecology and Systematics 26, 1-24]). This insight should not be lost in international rural development programs
Eco-social analysis of an East African agro-pastoral system: management of tsetse and bovine trypanosomiasis.
No full textA key constraint for development of many East African agro-pastoral communities is
African animal trypanosomiasis or nagana caused by Trypanosoma spp. and vectored by
species of tsetse flies (Glossina spp.). Suppression of trypanosomiasis through trapping of
tsetse fly populations was conducted from 1995 to 2005 at and near Luke, Southwest
Ethiopia. Odor baited mass trapping technology was used to suppress adult fly populations
to very low levels while tryponocidal drugs were used to treat trypanosome infections in
cattle. Data on ecological, economic and social variables were collected and analyzed in the
context of eco-social dynamics in the community.
The bio-economicmodel of Regev et al. [Regev,U., Gutierrez, A.P., Schreiber, S.J., Zilberman,
D., 1998. Biological and Economic Foundations of Renewable Resource Exploitation. Ecological
Economics 26, 227-242] and Gutierrez and Regev [Gutierrez, A.P., Regev, U., 2005. The
bioeconomics of tritrophic systems: applications to invasive species. Ecological Economics
52, 382-396]was used as amethodological framework for qualitative evaluation of the effects of
tsetse/trypanosomiasis suppression on ecological, economic and social aspects. An objective
function for single farmers was formulated to determine the optimal harvesting level of cattle,
exposed to high and low levels of risk from tsetse/trypanosomiasis, as measured by the
discount rate (δ) for a given base level pastoral resource (R=pasture or forage for cattle). The
socially optimal objective function for resource exploitation by all farmers is that which
maximizes the present value of utility of individuals expending revenues (consumption) from
the revenue stream in ways that enhance the quality of life and yet assures the persistence of
the resource base over an infinite time horizon (i.e., renewable resource sustainability).
The bio-economic model predicts that reducing risk (δ) from tsetse and disease increased
the cattle populations and their marginal value. The model also predicts that the interaction
of decreased δ and increased productivity (θ) can lead to increased human and cattle
populations and hence to over-exploitation of base resources (pastures) that lower
environmental carrying capacity and reduced sustainability.
Trap catches indicated that tsetse populations were reduced to very low levels, while the
disease prevalence decreased from 29% to 10%. This led to a substantial increase in cattle including oxen populations, increased calving rates, increased milk production and
increased the per-capita income. The availability of oxen allowed an increase in
cultivated land from 12 ha in 1995 to 506 ha in 2005. Revenues (consumption) were invested
in the purchase of more cattle and the establishment of a school for educating village
children. Increases in land allocated to crops and other sources of income were also found.
The bioeconomic model predicts the solution of the trypanosomiasis problems so
transforms the East African agro-pastoral communities that new social structures will be
required to cope with the ecological, economic and social consequences of this
technological changes on sustainable development (sensu [Goodland, R., 1995. The
concept of environmental sustainability. Annual Review of Ecology and Systematics 26, 1-
24]). This insight should not be lost in international rural development programs
A physiologically based tritrophic metapopulation model of the African cassava food web
No full textThe metapopulation dynamics of the African cassava food web is explored using a physiologically based tritrophic model. The interacting species are cassava, cassava mealybug and its natural enemies (two parasitoids, a coccinellid predator and a fungal pathogen), and the cassava greenmite and its natural enemies (two predators and a fungal pathogen). The metapopulation model is based on a single patch age-structured population dynamics model reported by Gutierrez et al. (Gutierrez, A.P., Wermelinger, B., Schulthess, F., Baumgärtner, J.U., Herren, H.R., Ellis, C.K., Yaninek, J.S., 1988b. Analysis of biological control of cassava pests in Africa: I. Simulation of carbon nitrogen and water dynamics in cassava. J. Appl. Ecol. 25, 901-920; Gutierrez, A.P., Neuenschwander, P. van Alphen, J.J.M., 1993. Factors affecting the establishment of natural enemies: biological control of the cassava mealybug in West Africa by introduced parasitoids. J. Appl. Ecol. 30, 706-721). The same model simulates the mass number dynamics of each plant or animal species in each patch and the movement of animals between patches. Movement is based on species specific supply–demand relations. The pathogen mortality rate is a simple function of rainfall intensity. The within-patch species composition, their initial densities, and the initial values of edaphic variables may be assigned stochastically. Sensitivity, graphical and multiple linear regression analyses are used to summarize the effects of spatial and resource heterogeneity on species dynamics. Important plant level effects on higher trophic levels are demonstrated, and recommendations are made as to the appropriate model for different ecological studies
UvA-DARE (Digital Academic Repository)
No full textRing1A is a transcriptional repressor that interacts with the Polycomb-M33 protein and is expressed at rhombomere boundaries in the mouse hindbrain Schoorlemmer, J.; Marcos-Gutierrez, C.; Were, F.; Martinez, R.; Garcia-Mendoza, E.; Satijn, D.P.E.; Otte, A.P.; Vidal, M
Eco-social Consequences of Disease Management in East African Agro-Pastoral Systems: Policy Implications.
No full text
STRUCTURE OF THE ART-SPACE IN THE STORY "I" BY A.P. POTEMKIN
No full textThe author performs the analysis of the art space structure in A.P. Potemkin's story "I". Several interrelated spatial models are allocated and described: household space, natural space, social space, psychological space, transpersonal space
Pressure drop and turbulence statistics in transpired pipe flow
No full textMeasurements of turbulent flow in a horizontal pipe subjected to wall transpiration are presented. Results include data on global flow rates and pressure drop, and local mean and fluctuating velocity profiles. Two distinct flow transpiration rates are studied, = / = 0.0005 and 0.001. The effects of flow transpiration on the friction-coefficient are compared with theoretical predictions. The theory furnishes predictions accurate to 3\%
Fully Turbulent Mean Velocity Profile for Purely Viscous non-Newtonian Fluids
No full textThe characteristic near wall behavior of turbulent flow of purely-viscous non-Newtonian fluids is discussed for both power-law (P.-L.) and Herschel-Bulkley (H.-B.) rheological models. A proper scaling is presented for H.-B. fluids to establish an analogy with power-law fluids with same flow index. To provide reference data for turbulent flow of non-Newtonian fluids, DNS simulations of power-law fluids are conducted in a rectangular channel for a large range of power-law indices ( = 0.5, 0.69, 0.75, 0.9, 1, 1.2). The DNS data show that the mean velocity profile in the viscous and logarithmic layers follow expressions of the form and respectively, where shows a logarithmic dependency on the flow index.Comparison with some experimental data shows the above formulation to be valid for Reynolds numbers (based on shear velocity) as high as 1000
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