Navegando por Assunto "Ecologia dos ecossistemas"

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Acesso aberto (Open Access)
Interação de Ucides cordatus Linnaeus, 1763 em manguezais da Ilha de Marajó: uma abordagem ecológica
(Universidade Federal do Pará, 2012) GOMES, Cleidson Paiva; FERNANDES, Marcus Emanuel Barroncas; http://lattes.cnpq.br/8943067124521530
The present study was carried out in the mangroves of Soure, Marajó Island, Pará, Brazil, where the great amount of freshwater intake allows the development of transition zones estuary/river defining the geobotanic limits for mangroves in the state of Pará and, hence, for the leaf-removing mangrove crab (Ucididae). For an ecological approach on the interaction between U. cordatus and mangrove forests the following issues were investigated: i) the relationship between the population characteristics of U. cordatus and different transition levels along the gradient of vegetation between mangrove forests and tidal valley forests, ii) the influence of environmental factors of such transition zones on patterns of size and density of U. cordatus population, iii) the impacts of herbivory of U. cordatus on the seedlings production and the possible effects on recruitment process of these seedlings for mangrove forests. Study sites were classified according to the transition level of the tidal várzea forests, and these values correlated with density and size values of U. cordatus population. In each study site the availability of food by litterfall rates, salinity, and indicators of fishing activities on these areas were determined. The impact of U. cordatus on the recruitment of mangrove stands was evaluated by estimating the rate of herbivory and predation on propagules. The results reveal that in the zone of "high transition" local conditions seem to limit U. cordatus stocks, showing that the density of this species population is much lower compared to those recorded in the "low transition" zone. However, areas of high transition offer more favorable conditions for development of the leaf-removing mangrove crab populations, especially with regard to the variability and availability of food and protection from human action in the region. The indicators of fishing activity on U. cordatus revealed that the mangrove forests of the lower transition zone are more subject to overexploitation, mainly for ease of access. The main via of impact on propagules was the consumption rate of 60%, being the rate of export of propagules by tides of only 1%, thus less relevant. U. cordatus may be considered the most important impact agent on the propagules production of these mangrove forests without showing selectivity by size or maturity of seedlings, being important in the regulation of recruitment rates and, hence, in the population dynamics of Rhizophora’s trees in the mangrove forests on the coastal zone of Marajó Island, in the Brazilian Amazon.
Acesso aberto (Open Access)
Manguezais do Pará: fauna de galerias perfuradas por teredo em toras de Rhizophora
(Universidade Estadual de Campinas, 1989-11-29) FERREIRA, Clara Pantoja; AMARAL, Antonia Cecília Zacagnini; http://lattes.cnpq.br/4597417616952392
In view of the large area the mangroves occupy in the State of Para’s coast their well-known importance and with the purpose to investigate their plant composition and to demonstrate the importance of the galleries bored in the logs as an habitat to several populations, periodic collects of Rhizophora lags were conducted. Measurements of temperature, pH, salinity and dissolved oxigen were accomplished. The study region was divided into 2 AREAS. The first one located at the Igarape-Curumbá mangrove (Ananindeua), where the collects were carried cut from April 1985 through January 1986 and the second in the Municípios of Benevides, Belém (Mosqueiro Island), Vigia and São Caetano de Odivelas, in which collects were carried out in July 1987 and January 1988. The mangrove stands from both AREAS are well-developped, specially those from Vigia and São Caetano de Odivelas, that are structurally the most developped. Rhizophora wangle was the dominant species in the 2 AREAS. A total of 45 species and 5022 individuals was recorded from the galleries of the 40 Rhizophora logs analysed. CRUSTACEA was the dominant taxon both for individuals and species numbers in almost all Subareas. The amphipode Grandidierella bonnieroides was the dominant species in the fauna composing 43,5% of the total number of individuals. The high in the AREA I reflects the high proport of common species among Subareas. The low values among the species of the Subareas from AREA II indicates that the composition of the fauna found inside the galleries is affected both by the physical and biological conditions to which the Rhizophora logs are submitted. The relatively high species diversity values of the 2 AREAS suggests the existence of stable conditions inside the galleries, allowing biological adaptations and interactions.