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| Legendre, P; Mcardle, Bh. |
| Values of a variable observed over a delimited geographic area are called a ''surface''. The problem we investigate is how to compare measures of the same area observed at two or more Sampling times. It is important to recognise that two different null hypotheses can be tested about the surface. The first is that the corresponding values in the surfaces differ only because of measurement or sampling error. The second is that the underlying process that generated the surfaces is the same. In the first case, the surfaces should have the same shape and values, while in the second case the surfaces might have different values, but if they still have the same means, variances and autocorrelation structures, the null hypothesis cannot be rejected. To prove the... |
| Tipo: Text |
Palavras-chave: Analysis of variance; Comparison of surfaces; Log-linear model; Sampling strategy; Trend surface analysis. |
| Ano: 1997 |
URL: http://archimer.ifremer.fr/doc/00093/20397/18064.pdf |
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| Lanctot, Jl; Legendre, P; Salvat, B. |
| The resistance to perturbations of reef-dwelling gastropod assemblages was studied on the seaward reefs of Fangataufa atoll (French Polynesia) after their exposure to atmospheric nuclear tests, a major man-made perturbation. We focused on two important aspects: (1) the temporal evolution of the densities of the most important species before and after the tests, and (2) the temporal evolution of the spatial structure of the assemblages. Three transects, crossing several geomorphological zones, were established on the seaward reefs of the atoll. Each transect was sampled at irregular time intervals during a twenty-year period. Several univariate and multivariate methods were used to study (1) the temporal fluctuations in species abundances and ranks, and (2)... |
| Tipo: Text |
Palavras-chave: Atmospheric nuclear tests; Clustering; Coral reefs; Gastropods; Perturbation. |
| Ano: 1997 |
URL: http://archimer.ifremer.fr/doc/00093/20394/18061.pdf |
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| Augustin, D; Galzin, R; Legendre, P; Salvat, B. |
| The interannual variability of the five dominant coral reef communities of the French Polynesia seascape (algae, corals, echinoderms, molluscs and fishes) was studied from 1990 to 1994 in the Tiahura sector of Moorea Island. Qualitative (species richness) and quantitative (cover percentage or density, depending on the type of community) stability is shown for benthic communities (algae, corals, echinoderms and molluscs), except for the macroalgae group and for bivalve species Tridacna maxima. In contrast, the fish community shows in its abundance a significant interannual variability characterized by a recruitment peak in 1991 and gradual and stochastic changes of densities for a few species. The bleaching events (in 1991 and 1994) and the cyclone Wasa... |
| Tipo: Text |
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| Ano: 1997 |
URL: http://archimer.ifremer.fr/doc/00093/20432/18099.pdf |
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