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

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1.
  • Dahlgren, Johan Petter, 1978- (författare)
  • Linking plant population dynamics to the local environment and forest succession
  • 2008
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Linking environmental variation to population dynamics is necessary to understand and predict how the environment influences species abundances and distributions. I used demographic, environmental and trait data of forest herbs to study effects of spatial variation in environmental factors on populations as well as environmental change in terms of effects of forest succession on field layer plants. The results show that abundances of field layer species during forest succession are correlated with their functional traits; species with high specific leaf area increased more in abundance. I also found that soil nutrients affect vegetative and flowering phenology of the forest herb Actaea spicata. The effect of nutrients shows that a wider range of environmental factors than usually assumed can influence plant phenology. Moreover, local environmental factors affected also the demography of A. spicata through effects on vital rates. An abiotic factor, soil potassium affecting individual growth rate, was more important for population growth rate than seed predation, the most conspicuous biotic interaction in this system. Density independent changes in soil potassium during forest succession, and to a lesser extent plant population size dependent seed predation, were predicted to alter population growth rate, and thereby the abundance, of A. spicata over time. Because these environmental factors had effects on population projections, they can potentially influence the occupancy pattern of this species along successional gradients. I conclude that including deterministic, as opposed to stochastic, environmental change in demographic models enables assessments of the effects of processes such as succession, altered land-use, and climate change on population dynamics. Models explicitly incorporating environmental factors are useful for studying population dynamics in a realistic context, and to guide management of threatened species in changing environments.
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2.
  • Arvanitis, Leena, 1959- (författare)
  • Plant polyploidy and interactions with insect herbivores
  • 2007
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Polyploidization has been suggested to be a common mechanism for plant speciation. Polyploidy is associated with changes in plant traits and altered habitat preference. Antagonistic and mutualistic animals are known to discriminate between plants based on variation in such plant traits, suggesting that interactions may have an important role in divergence of plant polyploids after the polyploidization. In this thesis, I investigated the effect of insect herbivores on divergence of plant polyploids in a system consisting of the predispersal seed predator butterfly Anthocharis cardamines, the bud gall forming midge Dasineura cardaminis, and tetraploids and octoploids of the herb Cardamine pratensis. Octoploid populations occurred more often in shaded and nongrazed habitats than tetraploids. Octoploid plants were larger and had fewer but larger flowers than tetraploids. Butterfly attack rates were higher in tetraploid than in octoploid populations, whereas the gall midge attacked only octoploids. These differences were associated with higher abundance of butterflies in sunny habitats and gall midges in shaded habitats. In contrast to the pattern at the population level, octoploid flower shoots were more likely to be attacked by the butterfly in sympatric populations. Also trait selection differed between ploidy levels, both in the absence and in the presence of herbivores. In a field experiment, butterfly preference did not alter the trait selection in tetraploids. In octoploids, the two herbivores did not change selection considered separately. However, their joint effect resulted in significant selection for smaller flower shoots and reduced selection on number of flowers. This thesis demonstrates that differences in habitat preference and phenotypic plant traits between polyploid cytotypes can lead to altered interactions with herbivores. Such differences in interactions with animals may alter not only the relative fitness of cytotypes but also trait selection within the respective ploidy type.
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3.
  • Boalt, Elin, 1976- (författare)
  • Ecology and evolution of tolerance in two cruciferous species
  • 2008
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Tolerance to herbivory is the ability of plants to maintain fitness in spite of damage. The goal of this thesis is to investigate the genetic variation and expression of tolerance within species, determine whether and in what conditions tolerance has negative side-effects, and how tolerance is affected by different ecological factors. Tolerance is investigated with special focus on the effects of different damage types, competitive regimes, history of herbivory, and polyploidization in plants. Studies are conducted as a literature review and three experiments on two cruciferous species Raphanus raphanistrum and Cardamine pratensis.In the tolerance experiments, plants are subjected to artificial damage solely, or in a combination with natural damage. A literature review was conducted in order to investigate the effects of damage method. We found that traits related to tolerance, such as growth and fitness were not as sensitive in regard to damage method as measures of induced chemical traits, or measures of secondary herbivory.Genetic variation of tolerance was demonstrated within populations of R. raphanistrum and between subspecies of C. pratensis. In R. raphanistrum, traits involved in floral display and male fitness were positively associated with plant tolerance to herbivore damage. A potential cost of tolerance was demonstrated as a negative correlation between levels of tolerance in high and low competitive regimes. I found no evidence of other proposed costs of tolerance in terms of highly tolerant plants suffering of reduced fitness in the absence of herbivores or trade-offs in terms of a negative association between tolerance to apical and leaf damage, or between tolerance and competitive ability. In C. pratensis, higher ploidy level in plants involved higher levels of tolerance measured as clonal reproduction. Furthermore, populations exposed to higher levels of herbivory had better tolerance than populations exposed to lower levels of herbivory. In this thesis, I demonstrate evidence of different components for the evolution of tolerance in plants: genotypic variation, selective factors in terms of costs and ploidization, and selective agents in terms of changing environment or herbivore pressure.
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4.
  • Mildén, Mikael, 1973- (författare)
  • Local and regional dynamics of Succisa pratensis
  • 2005
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)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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5.
  • Sandring, Saskia, 1974- (författare)
  • Plant-Animal Interactions and Evolution of Floral Display and Flowering Phenology in Arabidopsis lyrata
  • 2007
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • In this thesis, I combined comparative and experimental approaches to examine selection on reproductive traits, and population differentiation in the insect-pollinated, outcrossing, perennial herb Arabidopsis lyrata. More specifically, I (1) determined whether selection on flowering phenology and floral display can be attributed to interactions with pollinators and herbivores, (2) examined whether population differentiation in flowering phenology and floral display is correlated with current selection on these traits, and (3) tested for local adaptation from contrasting environments in Europe.A field experiment conducted in a Swedish population demonstrated, that interactions with pollinators may markedly affect selection on both floral display and phenology of flowering. In an alpine population in Norway, grazing damage to inflorescences strongly influenced selection on floral display. The results suggest that variation in the abundance of pollinators and herbivores should contribute to spatio-temporal variation in selection on flowering phenology and floral display in A. lyrata. A common-garden experiment showed that flowering phenology and floral display vary among Scandinavian populations of A. lyrata. For some traits patterns of population differentiation were consistent with differences in the direction and strength of phenotypic selection determined in comparisons (a) between an alpine population in Norway and a coastal population in Sweden, and (b) among coastal populations in Sweden. This suggests that current selection contributes to the maintenance of genetic differentiation in these traits.Adaptive differentiation among populations was examined in a reciprocal transplant experiment that included populations from three contrasting environments, alpine Norway, coastal Sweden and lowland, continental Germany. The experiment provided evidence for local adaptation, and indicated that populations have diverged in traits affecting plant establishment and early growth.
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6.
  • Toräng, Per, 1978- (författare)
  • Pollinators, Enemies, Drought, and the Evolution of Reproductive Traits in Primula farinosa
  • 2007
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • In this thesis, I combined comparative and experimental approaches to examine selection on reproductive traits and population differentiation in the insect-pollinated, self-incompatible, perennial herb Primula farinosa. More specifically, I (1) determined whether the effects of floral display and interactions with pollinators and seed predators, and plant reproductive success were frequency-dependent and affected by surrounding vegetation context, (2) examined the consequences of intermittent drought years on population dynamics using numerical simulations based on demographic data collected over seven years, (3) analyzed among-population differentiation in flowering phenology and reproductive allocation, and its relationship to soil-depth at the site of origin.A field experiment suggested that conspicuous plants facilitate inconspicuous plants in terms of pollinator attraction, and that the facilitation effect is contingent on the height of the surrounding vegetation. Further experiments revealed that both mutualistic and antagonistic interactions can result in frequency-dependent selection on floral display. Among inconspicuous plants, both fruit initiation, and damage from seed predators increased with the proportion of the conspicuous morph. The relative strength of these effects, and therefore their net outcome on the relationship between morph ratio and seed production varied among years.I combined information on vital rates and their relation to environmental conditions in simulations to predict future population viability in changing environments. Simulated stochastic population growth rate decreased with increasing frequency of drought years.Reproductive allocation varied significantly among populations both in the field and in a common-garden experiment, but was correlated with soil depth at the site of origin only in the field. The results suggest that among-population variation in reproductive effort in the field mainly reflects plastic responses to environmental conditions, and that this plasticity may be adaptive. The common-garden experiment suggested that the study populations have diverged genetically in flowering time.
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7.
  • Vanhoenacker, Didrik, 1971- (författare)
  • Selection on floral traits in Primula farinosa
  • 2008
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Flowers and inflorescences have evolved in relation to animals for at least 100 million years. Plants attract pollinators with large, conspicuous, bright-coloured or scented flowers. These display attributes, however, also attract herbivores. Optimal conspicuousness may therefore represent a trade-off between attractiveness to pollinators and vulnerability to herbivores. In a heterogenic landscape, the abundances of pollinators and herbivores vary, and this variation should cause the local net selection on floral traits to vary as well. This thesis investigates how pollinators and herbivores select for floral traits, how this selection is linked to interaction intensities, and what factors determine spatial variation in interaction intensity. I have studied the small perennial herb, Primula farinosa, and its interactions with pollinators, a seed predator moth, and grazers. The plant varies in several floral traits; most notably it displays a polymorphism in scape length. Results showed that pollinators selected for long scape, while the seed predator and grazers selected against long scape. Local net selection on scape length depended on interaction intensities of all three interactions. Scape morph also affected selection on number and size of flowers. We hypothesised that intensity of seed predation should depend on local population history of the specialised moth. However, the results from a 5-year survey suggests that patches were recolonized every year, and that the most important patch choice criteria were plant characteristics, such as mean inflorescence size and scape morph frequency. Within a geographic selection mosaic, local hot spots of plant evolution may not be random patches, but patches chosen by the agent of selection based on plant trait values. This thesis shows how spatial population ecology and herbivore dispersal behaviour are linked to mosaic interactions and trait evolution.
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8.
  • von Zeipel, Hugo, 1973- (författare)
  • The spatial and temporal dynamics of plant-animal interactions in the forest herb Actaea spicata
  • 2007
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Landscape effects on species performance currently receives much attention. Habitat loss and fragmentation are considered major threats to species diversity. Deciduous forests in southern Sweden are previous wooded pastures that have become species-rich communities appearing as islands in agricultural landscapes, varying in species composition. Actaea spicata is a long-lived plant occurring in these forests. In 150 populations in a 10-km2 area, I studied pre-dispersal seed predation, seed dispersal and pollination. I investigated spatio-temporal dynamics of a tritrophic system including Actaea, a specialist seed predator, Eupithecia immundata, and its parasitoids. In addition, effects of biotic context on rodent fruit dispersal and effects of flowering time and flower number on seed set, seed predation and parasitization were studied. Insect incidences of both trophic levels were related to resource population size and small Eupithecia populations were maintained by the rescue effect. There was a unimodal relationship between seed predation and plant population size. Seed predator populations frequently went extinct in small plant populations, resulting in low average seed predation. Parasitoids were present in large plant populations but did not affect seed predator density. Seed predators aggregated at edges, relaxing seed predation in patch interiors. Flowering phenology was unrelated to seed set and insect incidence. A higher flower number did not influence seed predation but was associated with higher seed set and a tendency for a higher parasitization rate. In the study on fruit dispersal more fruits were removed inside than outside populations. Within plant populations more fruits were removed from large aggregations. Overall, this thesis underlines the importance of plant-animal interactions during different phases of the life cycle. The spatial configuration of host plants plays an important role for the outcome of plant-animal interactions and trophic cascades.
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9.
  • Wallin, Lotta, 1975- (författare)
  • Plant Population Dynamics and Conservation in Wooded Hay-Meadows – Effects of Intensified Management
  • 2007
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • The decrease in number and area of managed hay-meadows over the last century, in combination with the reduction of traditional management, threatens the biodiversity connected to these habitats. I experimentally examined how management intensity affected meadow characteristics and long-term population viability of three vascular plant species in wooded hay-meadows on the Swedish island of Gotland in the Baltic Sea. I discovered that intensified management (extra raking and/or extra mowing) reduced the amount of litter and biomass, even in well-managed meadows. The effects of intensified management on population growth rate varied among species. Deterministic demographic models revealed that intensified management increased population growth rate in Succisa pratensis. Stochastic modelling confirmed this; all meadows displayed larger projected population sizes 50 years into the future with intensified management. Polygala amarella responded with lower growth rates in raked plots, a consequence of the plant’s morphology, which makes it prone to being pulled out by raking. Hypochoeris maculata had population growth rates close to unity, and showed no response to an increase in management. Examination of the life-history characteristics of Polygala amarella showed that the species’ strategy is aimed at reproduction and fast growth, which is in contrast to the other two species, with their success relying on the survival of older plants. The species-specific responses to management show that several species should be considered when evaluating management practices for conservation of semi-natural grasslands. Furthermore, I suggest that data on stage distributions alone may not be sufficient for identifying threatened populations.In a study of artificial dispersal between meadows, I found that establishment was twice as successful for planted plug-plants compared to sown seeds. Both methods may be useful for introducing or augmenting meadow populations, depending on access to seed sources and possibilities to nurse plants.An electronic coordinate measurement device for gathering location data to be used in demographic studies was developed. In the field, the device proved to be a simple and reliable method for locating individuals in permanent plots.
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10.
  • Östergård, Hannah, 1969- (författare)
  • Plant-seed predator interactions – ecological and evolutionary aspects
  • 2008
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Plant-animal interactions are affected by both abundance and distribution of interacting species and the community context in which they occur. However, the relative importance of these factors is poorly known. I examined the effects of predator host range, environmental factors, host plant populations, plant traits and fruit abortion on the intensity of pre-dispersal seed predation in 46 host populations of the perennial herb Lathyrus vernus. I recorded damage by beetle pre-dispersal seed predators, mainly Apion opeticum and Bruchus atomarius with different host ranges on L. vernus as well as on two additional host plants. Local seed predator population size was mainly influenced by plant population size, current seed production and beetle population size in the previous year, but was not strongly affected by connectivity. The monophagous seed predator was less abundant and had lower densities than the oligophagous. Both predator species had a strong ability to track fluctuations in seed production; intensity of predation increased with relative increases in seed production. Oligophagous predation on L. vernus increased with the abundance of alternative hosts, but presence of L. vernus did not affect predation on alternative hosts. Abundances and trait preferences differed among three co-occurring seed predators, but were also associated with the abundance of the other species. Overall, seed predation influenced selection on flower number. I found clear indications of seed predator offence but no obvious plant defence. The pattern of fruit abortion was associated with reduced plant fitness since the seed predator had an advanced ability to locate fruits with high probability of retention. Taken together, different factors influencing abundance of the seed predator species, different preferences, and context dependent trait selection are likely to result in complex spatio-temporal variation in overall seed losses and trait selection in the common host plant.
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