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- Csergoe, Anna-Maria, et al.
(författare)
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Two-scale modelling of Saponaria bellidifolia Sm. (Caryophyllaceae) abundance on limestone outcrops from its northern range periphery (Southeastern Carpathians)
- 2009
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Ingår i: PLANT ECOLOGY. - : Springer Science and Business Media LLC. - 1385-0237 .- 1573-5052. ; 203:2, s. 229-242
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Tidskriftsartikel (refereegranskat)abstract
- We modelled the effect of habitat heterogeneity on the abundance of the submediterranean Saponaria bellidifolia, a red list species in Romania. The study was designed at two scales: 100 and 0.5 m(2). At larger scale, generalized additive models and canonical correspondence analysis were used to model the density of ramets, whereas at microscale, binomial logistic regression was employed to model the species' occurrence. S. bellidifolia abundance responded sensitively to habitat type (classified as "grassy", "rocky" and "scree"), rather than to microclimatic variables. At both scales, habitat type was the best predictor of ramet abundance, followed by slope and vegetation cover. At 0.5 m(2), soil depth was also a good predictor of species occurrence. The data revealed that screes are the most suitable habitats for hosting relatively large populations of this rare species, because of occasional natural disturbances and presumably lower interspecific competition.
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| 3. |
- Hartel, Tibor, et al.
(författare)
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Pond and landscape characteristics - which is more important for common toads (Bufo bufo)? A case study from central Romania
- 2008
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Ingår i: Applied Herpetology. - : Brill. - 1570-7539 .- 1570-7547. ; 5:1, s. 1-12
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Tidskriftsartikel (refereegranskat)abstract
- The primary anthropogenic factor causing amphibian declines in Europe is habitat loss and fragmentation. Here we explore the effects of aquatic and landscape habitat variables on the adult counts of the Common Toad (Bufo bufo) in 43 ponds in central Romania surveyed between 2000 and 2005. Principal components analysis (PCA) identified two main factors, with which the adult counts can be related the first related to landscape variables (percentage of forest cover, presence/absence of roads and habitat corridors) and the second, to pond variables, in particular the presence/absence of fish, together accounting for 49% of the total variance. Analysis of variance (ANOVA) showed differences between ponds where toads were present or absent in factor loadings of both principal components, but only the landscape factor was significantly correlated with toad counts. These results highlight the role of landscape composition and configuration in maintaining toad populations in this area, and suggest a negative effect of landscape fragmentation. To efficiently protect amphibians in Romania, appropriate legislation and a close collaboration between landowners, landscape planners and herpetologists are needed.
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| 6. |
- Nemes, Szilard, 1977, et al.
(författare)
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Bias in odds ratios by logistic regression modelling and sample size.
- 2009
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Ingår i: BMC medical research methodology. - : Springer Science and Business Media LLC. - 1471-2288. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- Background: In epidemiological studies researchers use logistic regression as an analytical tool to study the association of a binary outcome to a set of possible exposures. Methods: Using a simulation study we illustrate how the analytically derived bias of odds ratios modelling in logistic regression varies as a function of the sample size. Results: Logistic regression overestimates odds ratios in studies with small to moderate samples size. The small sample size induced bias is a systematic one, bias away from null. Regression coefficient estimates shifts away from zero, odds ratios from one. Conclusion: If several small studies are pooled without consideration of the bias introduced by the inherent mathematical properties of the logistic regression model, researchers may be mislead to erroneous interpretation of the results.
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