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Sökning: WFRF:(Prentice Honor C)

  • Resultat 1-10 av 87
  • [1]234567...9Nästa
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  • Lönn, M, et al. (författare)
  • Gene diversity and demographic turnover in central and peripheral populations of the perennial herb Gypsophila fastigiata
  • 2002
  • Ingår i: Oikos. - : Wiley-Blackwell. - 1600-0706 .- 0030-1299. ; 99:3, s. 489-498
  • Tidskriftsartikel (refereegranskat)abstract
    • Within-population gene diversity (H-S) was estimated (using allozyme markers) for 16 populations of the perennial, outcrossing plant, Gypsophila fastigiata, on the Baltic island of Oland. The populations were characterized by data on extent, density, life-stages, and habitat diversity. Populations were classed as central or peripheral in relation to the distribution of ''alvar" (habitats with shallow, calcareous soils on limestone bedrock) on southern Oland. Three minimal adequate models were used to explain H-S and the proportions of juveniles and dead adults. In the first model, H-S was significantly lower in peripheral populations and there were no significant additional effects of other explanatory variables. The lower diversity in peripheral populations can be explained by a combination of genetic drift (in populations that vary in size in response to habitat fragmentation) and lower levels of interpopulation gene flow than in central populations. In the two life-stage models, peripheral populations had significantly larger proportions of both juveniles and dead adults indicating a greater demographic turnover than in the central populations. There were also significant effects of H-S and species diversity on the proportion of juveniles. The central or peripheral position of populations is the strop est predictor of both within-population gene diversity and life-stage dynamics in Oland G. fastigiata.
  • Prentice, Honor C, et al. (författare)
  • Changes in allozyme frequencies in Festuca ovina populations after a 9-year nutrient/water experiment
  • 2000
  • Ingår i: Journal of Ecology. - : Wiley-Blackwell. - 1365-2745 .- 0022-0477. ; 88:2, s. 331-347
  • Tidskriftsartikel (refereegranskat)abstract
    • 1 The grass Festuca ovina is an important constituent of the species-rich 'alvar' grasslands on the Baltic island of Oland. Levels of allozyme polymorphism are high and variation is known to be correlated with habitat variation (soil moisture, pH and depth). 2 A 9-year field experiment on species diversity provided replicate plots (in three sites) that had been subjected to six different experimental treatments (control; N + P + K; P + K; N + K; K; water). 3 Samples of F. ovina were collected and analyses of deviance were used to investigate associations between allele frequencies, at each of four polymorphic loci, and the nutrient/water treatments. We also used the models to estimate predicted values for the alleles in different nutrient/water treatments and in interactions involving the nutrient/water treatments and additional explanatory variables (vegetation height and clipping). 4 There were significant allozyme frequency differences between samples of F. ovina from the six different nutrient/water treatments in the grassland experiment. Frequencies in the fertilized or watered plots had diverged from those in the control plots. There were also significant allele-habitat associations (after the removal of site effects), especially at the Pgi-2 locus. 5 Soil moisture was the only variable that was common to this study and an earlier study of variation in F. ovina in natural habitats. In natural populations, the Pgi-2-2 allele was significantly associated with soil moisture and was more common in dry habitats. Our findings that the frequency of the Pgi-2-2 allele was significantly affected by the nutrient/water treatments, and that it was rarest in the treatment that involved the addition of extra water, were therefore as predicted. 6 The study supports the conclusion, from an earlier study of populations in unmanipulated grassland habitats, that selection is contributing to the fine-scale patterning of genetic variation in the alvar populations of F. ovina.
  • Rautenberg, Anja, et al. (författare)
  • Geographic and phylogenetic patterns in Silene section Melandrium (Caryophyllaceae) as inferred from chloroplast and nuclear DNA sequences
  • 2010
  • Ingår i: Molecular Phylogenetics and Evolution. - : Elsevier. - 1095-9513 .- 1055-7903. ; 57:3, s. 978-991
  • Tidskriftsartikel (refereegranskat)abstract
    • The phylogenetic relationships between the five dioecious species in Silene section Melandrium (Caryophyllaceae) and their putative hermaphrodite relatives are investigated based on an extensive geographic and taxonomic sample, using DNA sequence data from the chloroplast genome and the nuclear ribosomal ITS region. The hermaphrodite S. noctiflora (the type species of section Elisanthe) is distantly related to the dioecious species. With the exception of chloroplast sequences in one S. latifolia population from Turkey, the dioecious taxa form a strongly supported monophyletic group (Silene section Melandrium). The phylogenetic structure within section Melandrium differs between chloroplast and nuclear sequences. While there is extensive sharing of chloroplast haplotypes among all the dioecious species (the observed patterns reflect geographic structure), the nuclear ITS phylogeny shows a higher degree of taxonomic structure. Chloroplast-sharing by the section Melandrium species is most plausibly explained by a history of hybridization and extensive backcrossing. (C) 2010 Elsevier Inc. All rights reserved.
  • Reitalu, Triin, et al. (författare)
  • Determinants of fine-scale plant diversity in dry calcareous grasslands within the Baltic Sea region
  • 2014
  • Ingår i: Agriculture, Ecosystems & Environment. - : Elsevier. - 1873-2305 .- 0167-8809. ; 182, s. 59-68
  • Tidskriftsartikel (refereegranskat)abstract
    • We used an extensive dataset (1220 vegetation plots of 1 m(2)) to study vegetation gradients and fine-scale plant diversity in dry calcareous grasslands (including alvar grasslands) in the Baltic Sea region. The study area covers the entire European distributional range of alvar habitats: Sweden (Oland, Gotland, Gotaland), Estonia (Saaremaa, Hiiumaa, north Estonia, west Estonia), and western Russia (Izhora, lzborsk). Fine-scale plant diversity was characterized by species richness and standardized phylogenetic diversity (comparing the observed mean pairwise phylogenetic distance (MPD) with MPD values from random communities). Ordination techniques (DCA) were used to characterize the main vegetation gradient. Variables describing local environment, climate, the biogeographic composition of the plant communities, and geographic location were related to fine-scale species richness and phylogenetic diversity using variation partitioning techniques and linear mixed models. The main vegetation gradient in the dry calcareous grasslands in the Baltic Sea region had a strong geographic component, was associated with soil depth, species' stress- and disturbance-tolerance and the age of the grassland habitat. Fine-scale phylogenetic diversity and species richness were negatively associated suggesting that these two diversity components are influenced by different sets of environmental and historical parameters. Fine-scale species richness was unimodally associated with the main vegetation gradient, and the highest levels of species richness were found under intermediate environmental (disturbance, light conditions and temperature) conditions where there was a mixture of species from different biogeographic regions. In contrast to species richness, fine-scale phylogenetic diversity was negatively associated with the main vegetation gradient. The highest phylogenetic diversity was found in the extremely thin-soiled alvar grasslands in Gotaland and on the Baltic islands (especially on Oland) where the high phylogenetic diversity is likely to be a reflection of a long history of continuous openness that has allowed time for the "collection" of phylogenetically different species within these unique habitats. (C) 2012 Elsevier B.V. All rights reserved.
  • Reitalu, Triin, et al. (författare)
  • Small-scale plant species richness and evenness in semi-natural grasslands respond differently to habitat fragmentation
  • 2009
  • Ingår i: Biological Conservation. - : Elsevier. - 1873-2917 .- 0006-3207. ; 142:4, s. 899-908
  • Tidskriftsartikel (refereegranskat)abstract
    • The study explores whether small-scale species diversity, species evenness and species richness in semi-natural grassland communities are similarly associated with present management regime and/or present and historical landscape context (percentage of different land-cover types in the surroundings). Species diversity, evenness and richness were recorded within 44150 x 50 cm grassland plots in a 4.5 x 4.5 km agricultural landscape on bland, Sweden. Recent and historical land-cover maps (years 2004, 1959, 1938, 1835, and 1800) were used to characterize the present and past landscape context of the sampled vegetation plots. Partial regression and simultaneous autoregressive models were used to explore the relationships between species diversity measures (Shannon diversity, richness and evenness) and different explanatory variables while accounting for spatial autocorrelation in the data. The results indicated that species richness was relatively sensitive to grassland isolation, while the response of species evenness to isolation was characterized by a degree of inertia. Because the richness and evenness components of species diversity may respond differently to habitat fragmentation, we suggest that monitoring projects and empirical studies that focus on changes in biodiversity in semi-natural grasslands should include the assessment of species evenness - as a complement to the assessment of species richness. In addition, our results indicated that the development and persistence of a species-rich and even grassland vegetation was favoured in areas that have historically (in the 19th century) been surrounded by grasslands. Information on landscape history should, whenever possible, be incorporated into the planning of strategies for grassland conservation. (C) 2008 Elsevier Ltd. All rights reserved.
  • Siefert, Andrew, et al. (författare)
  • A global meta-analysis of the relative extent of intraspecific trait variation in plant communities
  • 2015
  • Ingår i: Ecology Letters. - : Wiley-Blackwell. - 1461-023X .- 1461-0248. ; 18:12, s. 1406-1419
  • Forskningsöversikt (refereegranskat)abstract
    • Recent studies have shown that accounting for intraspecific trait variation (ITV) may better address major questions in community ecology. However, a general picture of the relative extent of ITV compared to interspecific trait variation in plant communities is still missing. Here, we conducted a meta-analysis of the relative extent of ITV within and among plant communities worldwide, using a data set encompassing 629 communities (plots) and 36 functional traits. Overall, ITV accounted for 25% of the total trait variation within communities and 32% of the total trait variation among communities on average. The relative extent of ITV tended to be greater for whole-plant (e.g. plant height) vs. organ-level traits and for leaf chemical (e.g. leaf N and P concentration) vs. leaf morphological (e.g. leaf area and thickness) traits. The relative amount of ITV decreased with increasing species richness and spatial extent, but did not vary with plant growth form or climate. These results highlight global patterns in the relative importance of ITV in plant communities, providing practical guidelines for when researchers should include ITV in trait-based community and ecosystem studies.
  • Jonsson, Olle B, et al. (författare)
  • Allozyme diversity and geographic variation in the widespread coastal sedge, Carex arenaria
  • 2000
  • Ingår i: Diversity and Distributions. - : Wiley-Blackwell. - 1366-9516 .- 1472-4642. ; 6:2, s. 65-80
  • Tidskriftsartikel (refereegranskat)abstract
    • Allozyme electrophoresis was used to investigate the structure of genetic variation in the rhizomatous coastal sedge, Carex arenaria, throughout its European range — from the SW Iberian peninsula to the Baltic region. Material was sampled from 77 sites in five geographic regions. Nine of the 13 investigated loci were polymorphic in the total material and there were interregional differences in the number of polymorphic loci per site and the percentage of variable sites. In the Scandinavia/Baltic region only 61% of the sites contained at least one locus with more than one allele, whereas all the British and SW Iberian sites were variable. There was a general tendency for the regional frequencies of the less common alleles at individual loci to decline from SW to NE. The mean (over loci and sites) within-site gene diversity (H ¯site) was 0.064 (in calculations based on the number of observed multilocus allozyme genotypes within each sampling site). Although there was considerable variation between geographically adjacent sites, within-site diversity showed a general decrease from SW to NE in Europe. There were significant differences in within-region gene diversity (Hreg) for the four most variable loci between the five regions. Hreg generally decreased from SW to NE Europe and most loci showed the highest diversity in the SW Iberian peninsula and the Bay of Biscay regions. The mean (over loci) gene diversity in the total material (Htot) was 0.070 and the levels of diversity in Carex arenaria are substantially lower than is usual in rhizomatous sedges. The within-site, between-site and between-regional components of the total diversity were 92.4%, 2.5% and 5.1%, respectively. The low levels of overall gene diversity in C. arenaria and the successive decrease in diversity from SW to NE are interpreted in terms of the species' history of postglacial spread into northern Europe. Despite the overall northwards decrease in diversity, the widespread occurrence of less common alleles and the lack of regional deviations from Hardy–Weinberg genotype frequency expectations suggest that C. arenaria is not predominantly self-fertilized.
  • Ahlberg, Erik, et al. (författare)
  • "Vi klimatforskare stödjer Greta och skolungdomarna"
  • Ingår i: Dagens nyheter (DN debatt). - 1101-2447.
  • Tidskriftsartikel (populärvet., debatt m.m.)abstract
    • DN DEBATT 15/3. Sedan industrialiseringens början har vi använt omkring fyra femtedelar av den mängd fossilt kol som får förbrännas för att vi ska klara Parisavtalet. Vi har bara en femtedel kvar och det är bråttom att kraftigt reducera utsläppen. Det har Greta Thunberg och de strejkande ungdomarna förstått. Därför stödjer vi deras krav, skriver 270 klimatforskare.
  • Li, Yuanzhi, et al. (författare)
  • Habitat filtering determines the functional niche occupancy of plant communities worldwide
  • Ingår i: Journal of Ecology. - : Wiley-Blackwell. - 0022-0477. ; 106:3, s. 1001-1009
  • Tidskriftsartikel (refereegranskat)abstract
    • How the patterns of niche occupancy vary from species-poor to species-rich communities is a fundamental question in ecology that has a central bearing on the processes that drive patterns of biodiversity. As species richness increases, habitat filtering should constrain the expansion of total niche volume, while limiting similarity should restrict the degree of niche overlap between species. Here, by explicitly incorporating intraspecific trait variability, we investigate the relationship between functional niche occupancy and species richness at the global scale. We assembled 21 datasets worldwide, spanning tropical to temperate biomes and consisting of 313 plant communities representing different growth forms. We quantified three key niche occupancy components (the total functional volume, the functional overlap between species and the average functional volume per species) for each community, related each component to species richness, and compared each component to the null expectations. As species richness increased, communities were more functionally diverse (an increase in total functional volume), and species overlapped more within the community (an increase in functional overlap) but did not more finely divide the functional space (no decline in average functional volume). Null model analyses provided evidence for habitat filtering (smaller total functional volume than expectation), but not for limiting similarity (larger functional overlap and larger average functional volume than expectation) as a process driving the pattern of functional niche occupancy. Synthesis. Habitat filtering is a widespread process driving the pattern of functional niche occupancy across plant communities and coexisting species tend to be more functionally similar rather than more functionally specialized. Our results indicate that including intraspecific trait variability will contribute to a better understanding of the processes driving patterns of functional niche occupancy.
  • Löfgren, Oskar, et al. (författare)
  • Landscape history confounds the ability of the NDVI to detect fine-scale variation in grassland communities
  • Ingår i: Methods in Ecology and Evolution. - : British Ecology Society / John Wiley & Sons, Inc.. - 2041-210X. ; 9:9, s. 2009-2018
  • Tidskriftsartikel (refereegranskat)abstract
    • The NDVI is a remotely sensed vegetation index that is frequently used in ecological studies. There is, however, a lack of studies that evaluate the ability of the NDVI to detect fine-scale variation in grassland plant community composition and species richness. Ellenberg indicators characterize the environmental preferences of plant species—and community-mean Ellenberg values have been used to explore the environmental drivers of community assembly. We used variation partitioning to test the ability of satellite-based NDVI to explain community-mean Ellenberg nutrient (mN) and moisture (mF) indices, and the richness of habitat-specialist species in dry grasslands of different ages. The grasslands represent a gradient of decreasing soil nutrient status. If community composition is determined by the responses of individual species to the underlying environmental conditions and if, at the same time, community composition determines the optical characteristics of the vegetation canopy, then positive relationships between the NDVI and mN and mF are expected. Many grassland specialists are intolerant of nutrient-rich soils. If specialist richness is negatively related to soil-nutrient levels, then a negative association between the NDVI and specialist richness is expected. However, because grassland community composition is not only influenced by abiotic variables but also by other spatial and temporal drivers, we included spatial variables and grassland age in the statistical analyses. The NDVI explained the majority of the variation in mF, and also contributed to a substantial proportion of the variation in mN. However, variation in specialist richness and the lowest values of mN were explained by grassland age and spatial variables—but were poorly explained by the NDVI. Synthesis and applications. The NDVI showed a good ability to detect variation in plant community composition, and should provide a valuable tool for assessing fine-scale environmental variation in grasslands or for monitoring changes in grassland habitat properties. However, because the concentration of grassland specialists not only depends on environmental variables but also on the age and spatial context of the grasslands, the NDVI is unlikely to allow the identification of grasslands with high numbers of specialist species.
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