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The mosquito Aedes aegypti , the principal vector of dengue and yellow fever viruses, is an anthropophilic species adapted to urban environments, particularly to housing. A decisive factor in the proliferation of this species is ambient temperature, which has a direct influence on the vital rates of the species. Here we present a structured matrix population model for analyzing the effect of temperature on the population dynamics of Aedes aegypti . The model is structured following the four natural stages of the species: egg, larva, pupa and adult. A set of population projection matrices (one for each temperature between 5 and 30 °C), was constructed and parameterized using published data on the biology of the species. The output of the models showed that pupation does not occur at temperatures below 8 °C. The population's growth rate was calculated for temperatures between 11 and 30 °C, resulting in an increasing function showing that temperatures above 12 °C are sufficient for population growth. For each matrix, a sensitivity and elasticity analysis of the parameters was performed. Together with the results from the population stable distribution analysis, they suggest that policies aimed at reducing the abundance of Aedes aegypti should seek to lower the survival probability in the egg and larval stages. The population dynamics was simulated under different seasonal scenarios. This seasonal analysis allows asserting that the egg stage dominates the population dynamics at all seasons.

Gastrointestinal parasitism is one of the diseases that has the highest economic impact on the Argentinian beef production system, rendering it inefficient. In the region of the Humid Pampas, it has been estimated that 22 million dollars are lost annually because of the death of calves and 170 million dollars are lost in sub-clinic costs. A mathematical model with fuzzy parameters was constructed for the analysis of the free-living stages of gastrointestinal parasites, with the purpose of estimating the pool of L3 larvae available for migration to pasture and the levels of infection in pasture at any time of the year under different climatic conditions. The model is formulated in terms of a system of three difference equations. These equations describe the abundance of parasites in each of the successive stages of the population development. The model was calibrated and tested with data gathered through fieldwork carried out in Tandil (37°19′S, 59°08′05″W), province of Buenos Aires (Argentina) and the corresponding weather data. A comparison between model simulations and fieldwork data obtained in other locations achieved satisfactory results.

Ostertagia ostertagi is a nematode, predominantly affecting cattle in the Pampean region of Argentina. A mathematical model parametrized using fuzzy rule-based systems of the Takagi-Sugeno-Kant type (FTSK) for estimating the development time from egg to infecting larval stage L3 of the gastrointestinal parasite O. ostertagi is here proposed. The estimation of development time of O. ostertagi is essential for the generation of appropriate control mechanisms, since this provides information about the time when parasites are ready to migrate to pastures. For the purpose of reflecting the natural environmental conditions, the mean daily temperature is taken as the main and only regulator of the development time. Humidity conditions are considered to be sufficient for the normal development of the larvae. Hence the individual's daily growth is a function of its length and the mean temperature recorded on the previous day. It is expressed in terms of a difference equation with fuzzy parameters, which are defined using laboratory data. Model outputs are tested against results of field experiments. Simulation results are very satisfactory, yielding a mean estimation error (MEE) of 0.64 weeks, with variance 0.34, and a determination coefficient R 2 = 0.74. The model clearly exhibits an inverse relationship between development time and temperature both in controlled and in field conditions. It also exhibits a very sensitive response both to the order in which the temperature sequence occurs, – reproducing the differences observed between spring and autumn – and to the amplitude of the temperature range.

Capybara (Hydrochaeris hydrochaeris ) is the largest living rodent, widely distributed in South America, with a considerable potential as an economic resource. There are large populations in the region of Esteros del Ibera that could be exploited in a sustainable manner and contribute positively to the development of the region. Such exploitation requires to be done responsibly and following a specially designed management plan. In the particular case of wildlife management, a sustainable exploitation of a given species requires knowledge of its dynamics, its density in the area, and its vital rates, as well as understanding how the natural environment will respond to the proposed manipulation. It is also important to determine which environmental variables lead the population dynamics in each region. A mathematical model is a very convenient tool for analyzing possible strategies. This work presents a matrix population model structured in five stages. Sensitivity and elasticity analyses of the model provide an understanding of the effects of differentiated class-dependent survival and growth probabilities on the life cycle. A harvest term has been included in the model with the purpose of evaluating the sustainability of a given exploitation scenario or comparing different harvest strategies. The different strategies depend on the exploitation pattern, the exploitation intensity, and the season in which the harvest takes place. The purpose is to formulate a simple tool that can be understood by a manager without specific training. Hence, the software interface was specially designed for a user with elementary knowledge of vital parameters of the species. © 2005 Elsevier B.V. All rights reserved.

The objective of this work is to analyze at a regional scale the hydrometeorological and hydrological characteristics of the Esteros del Ibera, a vast freshwater wetland located in NE Argentina. Since water is the main driving force in the inland wetlands and variations in water level impose conditions on the behavior of vegetation and animal populations, the knowledge of the main hydrometeorological variables that affect the hydrology is essential. Data correlation analysis makes it possible to evaluate the observed changes in the wetland and to infer its response to regional climatic change. As a first approach, the construction of a topo-bathymetric map provides a basic tool for developing a digital elevation model (DEM) using a geographic information system (GIS) and models that are based on a spatial scale.

There are several freshwater systems associated to large rivers in South America, being the inland wetlands one of substantial significance from an environmental and ecological point of view. Largely sub-valued and unknown, the permanent-temporary flooded ecosystems related to the Parana River in Argentina and Paraguay must be studied in view to their conservation. In the particular case of the Ibera wetlands, their extension (14,000 km2), their inaccessibility, and the scarcity of available data need to be taken into account when attempting to study water dynamics. As a tool to understand the hydrology, main driving force of the ecosystem, a water balance was performed for analyzing the state of the system. As a result, a good agreement between measured water levels and calculated balance was encountered and the possibility of a non-previously considered ground-water inflow tested.

We propose an individual-based energy budget model of the Greater Rhea (Rhea americana) with the purpose of analyzing the population's recruitment. One remarkable characteristic of this species is that female rheas lay eggs communally and males incubate the eggs and care for the chicks without the assistance of females. The model is based on a system of equations daily updating the weight of each bird as a function of its ingestion rate and the energetic cost of its activity pattern. Ingestion rate is calculated from field experiments. Daily energetic costs are estimated from activity patterns observed in the field, taking into account gender and factors that influence behavior (e.g., photoperiod, season). Concatenating daily model outputs, the weight dynamics of an individual can be calculated over any given period of time. The possible factors that affect the successful breeding of the Greater Rhea and therefore population growth are analyzed using the model. Different reproductive strategies for each gender are analyzed and the minimal body weight, and thus energy reserves, that an individual needs to achieve for ensuring reproductive success is determined. Model outputs show that the reproductive success of males depends strongly on their body weight while females exhibit low nutritional requirements for producing eggs. An analysis of model outputs allows inferring that males in wild populations might not be able to breed in consecutive years but could successfully breed every other year. They also allow estimating the incidence that food availability has on population growth. Management strategies that are easy to implement in extensive and semi-extensive farms may allow obtaining male individuals capable of breeding every year. Fil: Simoy, Maria Veronica. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Ciencias Exactas. Instituto Multidisciplinario de Ecosistemas y Desarrollo Sustentable; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Canziani, Graciela Ana. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Ciencias Exactas. Instituto Multidisciplinario de Ecosistemas y Desarrollo Sustentable; Argentina Fil: Fernandez, Gustavo Javier. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ecología, Genética y Evolución; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Marinelli, Claudia Beatriz. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Ciencias Exactas. Instituto Multidisciplinario de Ecosistemas y Desarrollo Sustentable; Argentina

The model here presented describes the dynamics of adult Ostertagia ostertagi parasites in cattle in the field. The model also describes the population of infecting L3 larvae subject to the conditioning process while in the pasture as well as the inhibition–disinhibition process in ingested L4 larvae. The model has two modules: one for the conditioning process and the other for the parasitic stage. The first module determines the proportion of ingested L3 larvae that will go through an arrested stage of development, or hypobiosis, and for how long depending on the weather conditions and the length of the period of exposure in the pasture. The second one describes the adult population dynamics as disinhibiting larvae and recently ingested larvae accumulate in the animal. The model has a discrete daily step and is parameterized using fuzzy inference systems of the Mamdani type (FM). Given that the inhibition–disinhibition process is not yet fully understood, a series of perturbations on the different input variables were performed with the purpose of analysing the model's behavior. Simulations show that the adult population exhibits two maximal peaks of infection in the hosts in December–January (Summer) and April–May (Autumn). These high values are a consequence of hypobiotic larvae resuming their development at those times. Fil: Chaparro, Mauro Alejandro Eduardo. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Ciencias Exactas. Instituto Multidisciplinario de Ecosistemas y Desarrollo Sustentable; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Canziani, Graciela Ana. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Ciencias Exactas. Instituto Multidisciplinario de Ecosistemas y Desarrollo Sustentable; Argentina Fil: Fiel, Cesar Alberto. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Ciencias Veterinarias. Departamento de Sanidad Animal y Medicina Preventiva; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina