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Sökning: WFRF:(Ehrlén Johan) > (2005-2009)

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11.
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12.
  • Eriksson, Ove, et al. (författare)
  • Seedling recruitment and population ecology
  • 2008
  • Ingår i: Seedling Ecology and Evolution. - : Cambridge University Press, Cambridge. - 9780521873055 ; , s. 239-254
  • Bokkapitel (refereegranskat)
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13.
  • Herben, T, et al. (författare)
  • Longterm spatial dynamics of Succisa pratensis in a changing rural landscape : linking dynamical modelling with historical maps
  • 2006
  • Ingår i: Journal of Ecology. - : Wiley-Blackwell. - 0022-0477 .- 1365-2745. ; 94:1, s. 131-143
  • Tidskriftsartikel (refereegranskat)abstract
    • We attempt to explain the current distribution of a long-lived perennial plant, Succisa pratensis, in a rural landscape in southern Sweden by linking its population biology with documented changes in the landscape, using a dynamical, spatially explicit model incorporating population dynamics and spatial spreading of the plant. Changes in the landscape were inferred from historical maps (1850 and 1900) and aerial photographs (1945 and 2001). We tested whether predictions for the current species distribution are affected by assumptions about its early 19th century distribution, to determine whether recent history and current processes are dominant, and how past landscape changes determine current distributions. Initial conditions influence predictions of current distribution, suggesting that the current distribution still partly reflects the distribution of the species in the early 19th century. A period of 150 years is too short for Succisa to have spread extensively if dispersal parameters are given realistic values. Simulations in which present-day land-use patterns were imposed at earlier dates showed that changes in landscape structure over the past 175 years also had a strong effect on the present-day habitat occupancy and population sizes of Succisa. The dominant process for Succisanow is extinction from marginal habitats. It is therefore likely that the (relatively) high present-day occupation patterns are still due to much larger areas having been available in the past rather than to successful dispersal. Although the species has responded to landscape changes, there is little evidence of population sizes reaching equilibrium. Our approach shows that the wealth of landscape information available from historical maps can be linked with data on population biology by means of dynamical models that can make predictions about species dynamics.
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14.
  • Jonsson, Magnus, et al. (författare)
  • Genetic divergence of climatically marginal populations of Vicia pisiformis on the Scandinavian Peninsula
  • 2008
  • Ingår i: Hereditas. - 0018-0661 .- 1601-5223. ; 145:1, s. 1-8
  • Tidskriftsartikel (refereegranskat)abstract
    • Vicia pisiformis L. is a perennial leguminous plant with a main distribution in broadleaved forest-steppes of eastern Europe. The species is classified as endangered (EN) according to the IUCN red-lists in both Norway and Sweden, due to severe fragmentation, small population sizes and continuing population decline. The populations on the Scandinavian Peninsula constitute the northern limit of the species distribution and are mostly restricted to warm stony slopes with predominantly southern aspects. In this study we used the AFLP method, which is a high-resolution genetic fingerprint method. Samples were collected from 22 Scandinavian populations. The overall genetic structure was analysed in an AMOVA, in a Mantel test and through constrained correspondence analysis (CCA). The ordination scores representing non-geographic genetic divergence were extracted from the CCA and analysed in a linear model using habitat variables and population size as explanatory variables. We found (i) a strong geographic structure, (ii) significant genetic divergence between populations, (iii) that this genetic divergence remained significant even after removing the effect of geography in a partial CCA and (iv) that the remaining non-geographic part of genetic divergence (distance from the ordination centre) was associated with aspect, populations with a northern aspect were more genetically divergent. Aspect explains more variation than population size and is the only variable retained in the minimal adequate model. We suggest that local adaptation has caused this divergence from an expected geographical pattern of genetic variation. This explanation is further supported by the association between aspect and specific AFLP fragments. Many plant populations are relics of a different climate (Aguirre-Planter et al. 2000; Despres et al. 2002; Pico and Riba 2002). In response to long-term climate change, populations can either migrate towards a more favourable climate or adapt to the new conditions (delaVega 1996; Jump et al. 2006). Species with limited dispersal ability are at risk of reaching isolated dead-ends of decreasingly suitable habitat, without any suitable habitat within dispersal distance (Colas et al. 1997). Isolated populations have to use their inherent evolutionary potential and adapt to changes in environmental conditions, or they will go extinct. As population fragments go extinct, those that remain will become increasingly isolated from each other both spatially and also genetically as the level of gene flow declines with increasing distance. Such correlation between genetic dissimilarities and geographic distances, known as isolation by distance (Slatkin 1993; Wright 1943), when found, suggests a history of geographically limited gene flow (Kimura and Weiss 1964). On top of an isolation by distance pattern there might be other genetic structures to be found. Occasional long-distance dispersal events for example may disturb geographic patterns with puzzling allele distributions as a result (Nichols and Hewitt 1994). Genetic drift is a process that will affect any pattern of genetic variation in a random fashion. Local adaptation through natural selection is a process that, if sufficiently strong in comparison with gene flow and genetic drift, will create patterns where genetic differentiation is associated with certain environmental conditions (Wright 1951). Several studies have shown the importance of local adaptation of populations (reviewed by Kawecki and Ebert 2004) (see also Bonin et al. 2006; Knight and Miller 2004; Kolseth and Lönn 2005; Lönn et al. 1998). Local adaptation can be strong also at small spatial scales (Snaydon and Davies 1976; Lönn 1993) even though it is sometimes very limited in terms of the number of genes involved (Kärkkainen et al. 2004) Environmental variability provides a base for biological variation by imposing differentiated selection pressures resulting in local adaptation. Topography provides large environmental variation within a relatively small area and thereby provides a basis for small-scale local adaptations. Depending on the local topographic possibilities populations can either migrate up and down slopes or along the same altitude to a different aspect to find a suitable microclimate. The dispersal distance will be much shorter per degree of temperature change during altitudinal migration (Hewitt 1996), than during simple latitudinal migration across a flat landscape. Slope and aspect are two important topographic parameters that determine the influx level of solar radiation, especially towards the poles where the total global radiation decreases (Larcher 2003). Vicia pisiformis is an endangered poorly-dispersed long-lived forest herb with its main distribution across the semi-open broadleaved forest steppes of eastern Europe. The Scandinavian populations are believed to be climate relict populations from warmer times. Earlier genetic studies of V. pisiformis using allozymes, RAPD:s and morhology, have found low to very low levels of genetic variation (Gustafsson and Gustafsson 1994; Black-Samuelsson et al. 1997; Black-Samuelsson and Lascoux 1999). Therefore we used AFLP (amplified fragment length polymorphism) markers, which detect even very small genetic differences between individuals. AFLP mainly analyse neutral variation, as the major fraction of most genomes is assumed to be neutral. However, since the AFLP-fragments are distributed randomly throughout the whole genome some fragments may be situated so close to regions under selection that they become more or less linked to them. This linkage disequilibrium between molecular markers and regions under selection, often referred to as quantitative trait loci (QTL), forms the basis for both QTL-mapping and marker assisted selection (MAS), reviewed by Dekkers and Hospital (2002). Gardner and Latta (2006) for example, found QTL under selection in both natural environments and in the greenhouse. Markers have been found to be connected to biomass production (Cavagnaro et al. 2006) and environmental variation (Bonin et al. 2006; Jump et al. 2006; Porcher et al. 2006). In this study we examine 22 Swedish and Norwegian populations of Vicia pisiformis and ask (i) if there is genetic differentiation between these populations, (ii) if there is can it be explained in its entirety by geographic location or (iii) can it partly be explained by habitat characteristics, suggesting local adaptation, or population size, suggesting genetic drift. We show that populations are differentiated geographically and that genetic variation in addition to the geographical pattern is associated with habitat.
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15.
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16.
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17.
  • Lehtilä, Kari, et al. (författare)
  • Habitat change and demography of Primula veris : Identification of management targets
  • 2006
  • Ingår i: Conservation Biology. - 0888-8892 .- 1523-1739. ; 20:3, s. 833-843
  • Tidskriftsartikel (refereegranskat)abstract
    • Although the effects of deterministic factors on population viability often are more important than stochasticity, few researchers have dealt with the effect of deterministic habitat changes on plant population demography We assessed population viability for the perennial herb Primula veris L. and identified targets for management based on demographic data from five different habitat types representing different degrees of canopy closure. We conducted replicate studies at the border of the distribution area and in more central parts. Demographic patterns were similar between the two regions. Most study populations had a positive population growth, and only populations in late phases of forest succession showed consistently negative trends. The populations of open habitats had high seedling recruitment, and the populations of early and middle forest succession had high seed production. The importance of survival for population growth rate increased with increasing habitat closure, whereas the importance of growth and reproduction decreased. Results of the elasticity analysis suggested that the best method to manage decreasing late-successional populations is to increase survival of the largest individuals. The life-table response experiment (LTRE) analysis, however, showed that survival of the largest individuals contributed little to differences in population growth rates of different habitats, whereas seed production and growth of small individuals were more important. Moreover, direct perturbation of the performance of the largest stages showed that late-successional populations would not attain positive population growth even if the largest stages had no mortality at all. We conclude that restoration of recruitment is the only possibility for positive population growth in late-successional populations of P. veris, although the elasticities of recruitment transitions are low. Our results also suggest that retrospective demographic methods such as LIRE constitute an important and necessary complement to prospective methods such as elasticities in identifying management targets.
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18.
  • Lehtilä, Kari, et al. (författare)
  • Seed size as an indicator of seed quality : a case study of Primula veris
  • 2005
  • Ingår i: Acta Oecologica. - 1146-609X .- 1873-6238. ; 28:3, s. 207-212
  • Tidskriftsartikel (refereegranskat)abstract
    • Seed size is a widely accepted measure of seed quality, because many earlier studies have shown that large seeds have high seedling survival, growth and establishment. We tested whether ovule loss increases size of the remaining seeds and whether such size increase affects seedling establishment. We removed all except one flower from inflorescences of Primula veris L. (Primulaceae), a perennial hemicryptophyte herb, at a late stage of flowering. Flower removal (FR) increased seed size by 33% compared to the control plants. We then divided the seeds within each treatment to small, middle-sized and large seeds and carried out a sowing experiment in the field, Within each experimental group, seedling establishment was positively associated with seed size. However, despite size differences, seeds from the FIR and control groups had the same seedling establishment probability. Seeds from FR plants had a higher seedling emergence in May than those from control plants, but the number of seedlings alive per sowing plot in the late summer was the same in both experimental groups. Increase in seed mass after partial FR thus did not enhance seedling performance, although seed size variation due to other causes was positively correlated with seedling establishment. Further studies are needed to show whether plastic changes of seed size are usually adaptive or not.
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19.
  • Mildén, Mikael, 1973- (författare)
  • Local and regional dynamics of Succisa pratensis
  • 2005
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • Land use change is considered to be one of the biggest threat to global species diversity. In Sweden, abandonment of grazing is one of the most common reasons for decline in species richness in semi-natural grasslands. Today semi-natural grasslands often occur as more or less isolated fragments. The result for species that benefits from grazing is a smaller area of suitable habitat and higher extinction risks and a lowered ability to colonize new areas. Succisa pratensis is a long-lived perennial plant that benefits from grazing and is common in Swedish semi-natural grasslands. I have assessed the performance of Succisa pratensis at various spatial and temporal scales, in a Swedish rural landscape. I performed demographic matrix modelling of populations at grazed and ungrazed sites. A regional level was then added, by incorporating data collected from a large number of populations and habitat types into the matrix models and extinction risks over 50 years were calculated. A dynamic metapopulation model was created and the regional dynamics, in terms of colonisations resulting from long distance dispersal and population extinctions were examined. The effects of management history were incorporated into the model by using historical maps. In addition, I made an analysis of the impact of management history on the distribution and performance of four grassland species, using vegetation maps from 1945 and 2001. Local dynamics of Succisa pratensis was negatively affected by abandonment of grazing. Recorded population sizes were ten times higher in grazed sites than in ungrazed. The turnover rate of the system was estimated to about one extinction or colonisation per year. Both the simulation study and the analyses of vegetation maps suggested a pronounced legacy of management history in Succisa pratensis in the study landscape. Overall, the results of this thesis demonstrate the importance of management history for species in the rural landscape.
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20.
  • Mildén, Mikael, et al. (författare)
  • Metapopulation dynamics of a perennial plant, Succisa pratensis, in an agricultural landscape
  • 2006
  • Ingår i: Ecological Modelling. - : Elsevier B.V.. - 0304-3800 .- 1872-7026. ; 199:4, s. 464-475
  • Tidskriftsartikel (refereegranskat)abstract
    • Most metapopulation models neglect the local dynamics, and systems characterized by slow population turnover, time lags and non-equilibrium, are only rarely examined within a metapopulation context. In this study we used a realistic, spatially explicit, dynamic metapopulation model of a long-lived grassland plant, Succisa pratensis, to examine the relative importance of local population dynamics, and short and long-distance dispersal of seeds. Using both vegetation composition and sowing experiments we identified 94 occupied and 43 unoccupied, but suitable, habitat patches in a 7-km2 landscape. Local population dynamics were studied in permanent plots in five populations. Simulation results showed that the colonization and extinction dynamics of S. pratensis were slow with about one colonization or extinction per year and the time frame for the population system to attain equilibrium in a constant landscape was several thousands of years. Sensitivity analyses demonstrated that occasional long-distance dispersal had a large influence on population turnover rates whereas regular short-distance dispersal had little effect. Our model also allowed us to assess how demographic processes affect not only local population growth but also regional dynamics. Fecundity was more important, compared with growth and survival, in a metapopulation context than when considered only within populations. The effect of landscape development was examined through different land-use scenarios and suggested that S. pratensis only very slowly colonizes new habitats that are made available. Our results with S. pratensis in an agricultural landscape show that long-distance dispersal and colonization dynamics play an important role for the regional distribution in long-lived plants but that time lags, and thus the effect of landscape history, are also very important.
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