| 1. |
- Dahlgren, Johan Petter, 1978-
(författare)
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Linking plant population dynamics to the local environment and forest succession
- 2008
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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, et al.
(författare)
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Plant ploidy level influences selection by butterfly seed predators
- 2008
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Ingår i: Oikos. ; 117, s. 1020-1025
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Tidskriftsartikel (refereegranskat)abstract
- Polyploidization is a common route to plant diversification. Polyploids often differ from their progenitors in size, flower number, flower size and flowering phenology. Such differences may translate into differences in the intensity of interactions with animals. Here we investigated the impact of the ploidy-related differences in tetraploids and octoploids of the perennial herb Cardamine pratensis on pre-dispersal seed predation by the butterfly Anthocharis cardamines. The probability of escaping attack was lower for octoploids than for tetraploids, even after accounting for the fact that octoploids were larger and had fewer flowers than tetraploids. Flower shoot size was correlated with probability of attack in tetraploids but not in octoploids. Differences in plant traits associated with polyploidization can alter interactions with animals, and animal-mediated differences in trait selection between ploidy types can contribute to their further divergence.
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| 3. |
- Boalt, Elin, 1976-
(författare)
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Ecology and evolution of tolerance in two cruciferous species
- 2008
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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. |
- Eriksson, Ove, et al.
(författare)
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Seedling recruitment and population ecology
- 2008
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Ingår i: Seedling Ecology and Evolution. - : Cambridge University Press, Cambridge. - 9780521873055 ; , s. 239-254
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Bokkapitel (refereegranskat)
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| 5. |
- Jonsson, Magnus, et al.
(författare)
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Genetic divergence of climatically marginal populations of Vicia pisiformis on the Scandinavian Peninsula
- 2008
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Ingår i: Hereditas. - : Springer Science and Business Media LLC. - 0018-0661 .- 1601-5223. ; 145:1, s. 1-8
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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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| 6. |
- Toräng, Per, et al.
(författare)
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Mutualists and antagonists mediate frequency-dependent selection on floral display
- 2008
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Ingår i: Ecology. - : Wiley. - 0012-9658 .- 1939-9170. ; 89:6, s. 1564-1572
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Tidskriftsartikel (refereegranskat)abstract
- Theory predicts that, with conflicting selection pressures mediated by mutualists and antagonists, alternative reproductive strategies can be maintained by negative frequency-dependent selection if it results in rare-morph advantage. We combined field experiments and surveys of natural populations to determine whether selection on. oral display is frequency dependent in the self-incompatible herb Primula farinosa, which is polymorphic for inflorescence height and occurs in a short-scaped and a long-scaped morph. Among short-scaped plants, both pollination success, quantified as initiation of fruits and seeds, and seed predation were positively correlated with the relative frequency of the long-scaped morph. The relative strength of these effects and the direction of the resulting frequency-dependent selection on scape morph varied among years and populations. The results suggest that both mutualists and antagonists may mediate frequency-dependent selection and that frequency dependence may vary from positive to negative with rare-morph advantage, depending on the relative strength of these interactions.
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| 7. |
- Vanhoenacker, Didrik, 1971-
(författare)
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Selection on floral traits in Primula farinosa
- 2008
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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. |
- Ågren, Jon, et al.
(författare)
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Spatio-temporal variation in fruit production and seed predation in a perennial herb influenced by habitat quality and population size
- 2008
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Ingår i: Journal of Ecology. - : Wiley. - 0022-0477 .- 1365-2745. ; 96:2, s. 334-345
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Tidskriftsartikel (refereegranskat)abstract
- 1. In patchily distributed plant species, seed production is likely to be influenced both by local abiotic factors affecting plant size and conditions for fruit maturation, and by population characteristics affecting the intensity of interactions with mutualists and antagonists. However, the relative importance of these effects is poorly known. 2. We used multiple regression and path models to examine the importance of abiotic factors (sun exposure, soil depth) and population characteristics (size, density and connectivity) for variation in flower and fruit production and intensity of seed predation among 39 populations of the long-lived herb Vincetoxicum hirundinaria in three consecutive years. In addition, we manipulated water availability in a field experiment and recorded short-term and long-term effects on fruit output, and conducted a supplemental hand-pollination experiment. 3. Flower production varied little, while fruit initiation, fruit abortion and fruit predation varied considerably among years. Sun exposure and soil depth affected fruit production per plant indirectly and positively through their effects on flower number. Population density affected fruit production negatively through its effect on flower number. Both fruit initiation and the proportion of fruits attacked by the tephritid fly Euphranta connexa were related positively to population size. 4. The number of full-size fruits per plant was related positively to sun exposure and population size in two years each, and related negatively to population density in one year. However, because of seed predation, the number of intact mature fruits was related significantly to population characteristics in only one of three years. 5. The field experiments showed that both shortage of water and insufficient pollination may limit fruit set in V. hirundinaria. 6. Synthesis. These results demonstrate that the relative importance of local abiotic conditions and population characteristics may vary considerably along the chain of events from flower formation to intact fruit, and also among years. They further show that, at least in species with a naturally patchy distribution, connectivity may be relatively unimportant for variation in reproductive output compared to effects of habitat quality, population size and density.
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| 9. |
- Östergård, Hannah, 1969-
(författare)
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Plant-seed predator interactions – ecological and evolutionary aspects
- 2008
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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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