Browsing by Issue Date, starting with "2007-08"
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- A conservation trade-off? Interspecific differences in seahorse responses to experimental changes in fishing effortPublication . Curtis, Janelle M. R.; Ribeiro, Joaquim; Erzini, Karim; Vincent, Amanda C. J.1. A 2-year experimental seining programme and underwater visual censuses were undertaken to quantify the direct effects of active demersal fishing on the population structure and relative abundance of two sympatric seahorse species of conservation concern: the European long-snouted seahorse, Hippocampus guttulatus Cuvier 1829 and the short-snouted seahorse, Hippocampus hippocampus L. The influence of habitat preference on population-level responses to changes in habitat structure following a reduction in fishing effort was also investigated. 2. It was predicted that the benthic habitat would be more structurally complex after fishing ceased and that seahorse densities would increase in response to reduced fishing mortality. Furthermore, it was predicted that the magnitude of the increase in density would be greater for H. guttulatus than for H. hippocampus, because the former species prefers complex vegetated habitats while the latter species uses sparsely vegetated habitats. 3. As predicted, the amount of habitat cover increased significantly when seining ceased, primarily through increases in the abundance of drifting macroalgae and unattached invertebrates. Despite similarities in life histories, the two seahorse species responded differently in terms of magnitude and direction to reduced fishing effort: the abundance of H. guttulatus increased significantly while H. hippocampus decreased in abundance. 4. Results suggest that active demersal fishing may influence the magnitude and direction of the responses of benthic marine fishes to exploitation through its impacts on habitat structure. An increase in habitat cover appeared to favour higher densities of H. guttulatus when seining effort was reduced. By contrast, repeated seining, which maintained less complex habitats, appeared to favour greater abundances of H. hippocampus. 5. Given differences in habitat preference among benthic marine fishes subject to incidental capture in fisheries, simultaneous attempts to manage populations of sympatric species may require complementary strategies that support the persistence of diverse habitat types. Copyright (c) 2006 John Wiley & Sons, Ltd.
- Genetic sub-structure and intermediate optimal outcrossing distance in the marine angiosperm Zostera marinaPublication . Billingham, M. R.; Simões, T.; Reusch, T. B. H.; Serrão, EsterThe spatial distribution of genetic variability depends on the spatial patterns of clonal and sexual reproduction, gene flow, genetic drift and natural selection. Species with restricted dispersal may exhibit genetic structuring within populations with immediate neighbours being close relatives, and may show differentiation among populations. Genetic structuring of a species may have important genetic, evolutionary and ecological consequences including distance-dependent mating success. In this study we used microsatellite markers to show that clones of Zostera marina in a population in the Ria Formosa, Portugal, were aggregated and covered distances of up to 3–4 m. Clones within 4 m of each other exhibited significant and positive coancestry values, reflecting the limited seed dispersal of this species. Hand-pollinations between near (0–10.9 m), intermediate (11–32 m) and far (15 km) individuals resulted in similar levels of seed set, although the near pollinations had higher, although not statistically significant, levels of seed abortion during maturation. Seeds from intermediate-distance pollinations had a significantly higher proportion of seeds germinate and shorter germination time than both the near and far seeds. Similarly, the average number of seedlings produced per pollination, used as an overall estimate of fitness, was significantly greater for the intermediate distance when compared to both near and far pollinations. These results suggest that the genetic structuring observed may result in both inbreeding and outbreeding depression, which gives rise to an intermediate optimal outcrossing distance.
- Turbo detection for the uplink of CP-Assisted DS-CDMA systemsPublication . Silva, Paulo; Dinis, RuiIn this paper we consider the use of SDMA (Space Division Multiple Access) techniques for the uplink of MC-CDMA systems (MultiCarrier -Coded Division Multiple Access) where the transmitted signals face strong nonlinear distortion effects. We define an iterative receiver that jointly performs a turbo-MUD (Multiuser Detection) as well as estimation and cancellation of the nonlinear distortion effects.
- A turbo SDMA receiver for strongly nonlinearly distorted MC-CDMA signalsPublication . Silva, Paulo; Dinis, RuiIn this paper we consider the use of SDMA (Space Division Multiple Access) techniques for the uplink of MC-CDMA systems (MultiCarrier -Coded Division Multiple Access) where the transmitted signals face strong nonlinear distortion effects. We define an iterative receiver that jointly performs a turbo-MUD (Multiuser Detection) as well as estimation and cancellation of the nonlinear distortion effects.
- Metodologias de previsão baseadas em modelos de índices de difusão – uma aplicação a variáveis da economia portuguesaPublication . Andraz, Jorge Miguel; Gouveia, Pedro; Rodrigues, Paulo M. M.Metodologias de previsão baseadas em modelos de índices de difusão - uma aplicação a variáveis da economia Portuguesa.
- Do código aberto ao acesso livre: soluções OSS para informatização de bibliotecasPublication . Mariano, Alexandra de Brito; Dias, MiguelApresentação de algumas soluções concretas de software livre para informatização de bibliotecas.