858 research outputs found

    Genetic erosion in the snail <i>Littoraria subvittata</i> (Reid, 1986) due to mangrove deforestation

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    In tropical coastal ecosystems mangrove forests are important as feeding, spawning, breeding and nursery grounds for many marine species. High human population pressure in coastal areas has led to the loss and deterioration of mangrove habitats. Solar salt production can affect these habitats along the East African coast. Littorinid snails live on mangrove trees, forming an important component of the mangrove ecosystem and have been used as bioindicators of environmental health and community stress. Littoraria subvittata is the most abundant littorinid species in mangroves along the East African coast. Partial mitochondrial cytochrome oxidase subunit 1 (COI) gene sequences of 298 individuals were used to assess the impact of mangrove deforestation at salt ponds on the genetic diversity and structuring of L. subvittata populations, as well as to infer the demographic history of the species. Nucleotide and haplotype diversities were found to be lower in samples from mangroves at salt ponds than in samples from natural mangroves. The mean nucleotide diversity was 0.049 ± 0.036% and 0.115 ± 0.068% in mangroves at salt ponds and natural mangroves, respectively. The mean haplotype diversity was 0.23 ± 0.14 and 0.50 ± 0.14 in mangroves at salt ponds and natural mangroves, respectively. Analysis of molecular variance (AMOVA) detected a significant population structure (Фst = 0.049; P ct = 0.022; P st = 0.054, P st = −0.0026, P = 0.64). Reduced effective population size was observed in most samples from mangrove sites at salt ponds compared with natural mangrove. The direction of migrants was mostly from salt ponds to natural mangroves. These results show that salt ponds have a negative impact on the genetic diversity of L. subvittata populations and modify the population's genetic structure

    Seed Production of Native Grassland Plants

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    2D mixed hybrid FEM of lanir model

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    Osmoelastic media have large negatively charged groups attached to the solid matrix. Due to the fixed charges, the total ion concentration inside the medium is higher than in the surrounding fluid. This excess of ion particles leads to an osmotic pressure difference, which causes swelling of the medium. Lanir's osmoelastic model assumes that small ions are always in equilibrium with the external salt concentration. This means that ion contribution is neglected and the medium is described by two constituents only: the solid and the fluid. In this paper, we implemented Lanir model using MHFEM (Mixed Hybrid Finite Element Method) for consolidation experiment in both 1D and 2D cases, with result verification with analytical solution in 1D. The constituents are assumed to be incompressible. Infinitesimal deformations are assumed. The material is linear elastic, isothermal, isotropic, homogeneous and fully saturated.</p
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