786 resultados para Theoretical ecology


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The goal of this paper is to develop a model of financial intermediation analyze the impact of various forms of taxation. The model considers in a unified framework various functions of banks: monitoring, transaction services and asset transformation. Particular attention is devoted to conditions for separability between deposits and loans. The analysis focuses on: (i) competition between banks and alternative financial arrangements (investment funds and organized security markets), (ii) regulation, and (iii) bank's monopoly power and risk taking behavior.

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El projecte de recerca s'ha basat en el projecte Miquel Martí i Pol, que ha consistit en la creació i manteniment d'un jardí dedicat a la memòria del poeta, amb persones en situació d'exclusió social (per motius de malaltia mental, immigració, pobresa) i estudiants de teràpia ocupacional de la Universitat de Vic, des d'una sinergia única entre la Universitat de Vic i institucions públiques, socials i empresarials. La recerca ve a cobrir la falta de coneixement sobre l'impacte terapèutic de la jardineria, com afirmava Sempik al 2003. Així mateix, genera coneixements sobre l'ocupació humana, la ciutadania, les comunitats inclusives, les aliances estratègiques i sobre noves praxis educatives en el marc del nou Espai Europeu d'Educació Superior (EEES). El marc teòric s'ha basat en una visió transdisciplinària, des de l'educació, la filosofia, la psicologia, la sociologia, la teràpia ocupacional, la política, l'ecologia i l'antropologia. S'ha desenvolupat una recerca inspirada per la investigació acció participativa que ha aprofundit en el significat que ha tingut aquesta experiència per a les persones implicades en el procés de creació del jardí: les persones procedents de col•lectius en situació d'exclusió, els estudiants, així com els representants de les institucions públiques, socials, empresarials i la pròpia Universitat de Vic. Així es van desenvolupar una sèrie d'entrevistes a fons i formularis amb 5 jardiners; 2 estudiants; la Consellera d'Acció Social de l'Ajuntament de Vic; el Conseller d'Acció Social del Consell Comarcal d'Osona; el President de Caritas; la terapeuta ocupacional de la Fundació Centre Mèdic Psicopedagògic d'Osona; la Rectora de la Universitat de Vic; la Directora de l'EUCS i el President del Rotary Club. Els temes que han sorgit en la recerca són: La construcció de l'ocupació significativa; la jardineria com a font de benestar; un espai de bellesa; la dignitat de la ciutadania; la creació de comunitats inclusives; una Universitat al servei de la Humanitat: noves praxis educatives; l'art de les aliances estratègiques i de les sinergies. Els coneixements generats tenen relació amb els estudis de teràpia ocupacional, així com per a educació social, infermeria, psicologia i ciències ambientals. A més a més són una aposta per al desenvolupament de noves praxis educatives en el nou EEES. El treball ha estat qualificat com a excel•lent per unanimitat del tribunal.

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It has been predicted on theorerical grounds (Sibly & Calow, 1983; Taylor & Williams, 1984) that optimal offspring size should be highly sensitive to juvenile growth and survival rates. To test such models, genetically-identical individuals of Simicephalus vetulus were reared at different temperatures and monitored for offspring size and juvenile growth rate. As adult size correlates negatively with temperature, an analysis of covariance was performed to separate the effects of temperature and maternal size. The result is that offspring size indeed correlates negatively with juvenile growth rate. Comparisons are made with field observation of several authors on seasonal variation of offspring size and alternative explanations are discussed. It is concluded that present experiments support the prediction of the theoretical models.

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A study on the ecology of phlebotomine sandfly fauna in a restricted focus of cutaneous leishmaniasis in northern Venezuela was undertaken in order to investigate the species responsible for the transmission. The study area and catching methods for phlebotomine sandflies are described. A total of 9,061 females and 1,662 males were collected during a year-term study. 12 species of Lutzomya and 1 species of Brumptomya sp. were identified. Absolute and relative abundance and ocurrence for each species were determined. The rel ative occurrence allowed to distinguish the common species, viz. L. panamensis, L. ovallesi, L. gomezi, L. tinidadensis, L. atroclavata, L. cayennensis, L. shannoni and L. olmeca bicolor from the rare species vis., L. punctigeniculata, L. rangeliana, L. evansi and L. dubitans. General comments on the species composition of the sandfly fauna in this locality are made.

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The ecology of phlebotomine sandflies in an endemic focus of cutaneous leishmaniasis in Northern Venezuela (San Esteban, Carabobo State) was investigated through a year-term study. Three different habitats: viz. a house, a pridomestic area and a sylvatic area, were covered and the species composition, the abundance and occurrence of each species were analyzed in relation to the habitats, catching methods and hour of catching. L. panamensis, L. gomezi and L. ovallesi are the species which bite man, although almost exclusively at night. All of them hide by day and are common in the sylvatic area. Moreover, L. panamensis and L. gomezi successfully approach the house and seem to settle in the peridomestic area. L. shannoni and L. olmeca bicolor also approach and accidentally bite man. L. trinidadensis, L. atroclavata and L. cayennensis are the common non-antrhopophilic species in the area.

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A one year-long study (March 1979-March 1980) was carried out at San Esteban, an endemic focus of cutaneous leishmaniasis in Northern Venezuela, with the aim of observing the seasonal fluctuation of the local phlebotomine sandflies species. The influence of climatic factors (temperature, relative humidity and rainfall) on population dynamics was analyzed in three collecting sites - a house, a peridomestic area and a sylvatic region. Among anthropophilic species, L. panamensis behaved as a wetseason species, the mean minimum relative humidity being the critical factor influencing the total number of individuals. When the population density of this fly decreased, it was successfully replaced by L. ovallesi, a dry-season species. On the other hand, seasonal variations of L. gomezi were more strongly affected by the temperature.

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An attempt has been made to correlate the monthly incidence of human leishmaniasis with the temporal distribution of sandfly species at San Esteban, Northern Venezuela. Upon statistical analysis, the seasonal fluctuation of L. ovallesi population correlated strongly with the human disease, while the dynamics of L. panamensis, generally believed to be the vector in the Central area of the country, showed only a very weak correlation. These findings support the hypothesis that L. panamensis might not be the main or unique species responsible for the transmission in this area and that L. ovallesi and additionally L. olmeca bicolor might be involved in the epidemiology of the disease.

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The dispersal process, by which individuals or other dispersing agents such as gametes or seeds move from birthplace to a new settlement locality, has important consequences for the dynamics of genes, individuals, and species. Many of the questions addressed by ecology and evolutionary biology require a good understanding of species' dispersal patterns. Much effort has thus been devoted to overcoming the difficulties associated with dispersal measurement. In this context, genetic tools have long been the focus of intensive research, providing a great variety of potential solutions to measuring dispersal. This methodological diversity is reviewed here to help (molecular) ecologists find their way toward dispersal inference and interpretation and to stimulate further developments.

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Study Objectives: Interspecific variation in sleep measured in captivity correlates with various physiological and environmental factors, including estimates of predation risk in the wild. However, it remains unclear whether prior comparative studies have been confounded by the captive recording environment. Herein we examine the impact of predation pressure on sleep in sloths living in the wild. Design: Comparison of two closely related sloth species, one exposed to predation and one free from predation. Setting: Panamanian mainland rainforest (predators present) and island mangrove (predators absent). Participants: Mainland (Bradypus variegatus, 5 males and 4 females) and island (Bradypus pygmaeus, 6 males) sloths. Interventions: None. Measurements and Results: EEG and EMG activity were recorded using a miniature data logger. Although both species spent between 9 and 10 hours per day sleeping, the mainland sloths showed a preference for sleeping at night, whereas island sloths showed no preference for sleeping during the day or night. EEG activity during NREM sleep showed lower low-frequency power, and increased spindle and higher frequency power in island sloths when compared to mainland sloths. Conclusions: In sloths sleeping in the wild, predation pressure influenced the timing of sleep, but not the amount of time spent asleep. The preference for sleeping at night in mainland sloths may be a strategy to avoid detection by nocturnal cats. The pronounced differences in the NREM sleep EEG spectrum remain unexplained, but might be related to genetic or environmental factors.