| 1. |
- Andersson, Petter, 1975-
(författare)
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The importance of search behavior and movements for spatial distributions of herbivorous insects
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Insect populations commonly show large spatial variation in density, and much variation have been shown to be explained by the search behavior applied by the insect when locating habitat patches. This thesis explores the importance of odor-mediated attraction for immigration rates of herbivorous insects in relation to the size of the patches and the density of host plants within the patches. By using electroantennogram and measuring moth antennal responses to sex pheromones and thereby estimating the relative odor-mediated attraction from odor patches in field experiments (Paper I, III), I show that the length of the odor plumes emanating from the patches increase proportional with the square-root of the number of odor sources. In laboratory and field experiments (with the weevils Cionus scrophulariae and C. tuberculosus and the host plant figwort Scrophularia nodosa; Paper II) and meta-analyses on multiple insect herbivores (Paper III), I examined whether the relative increase in plume length could also predict the immigration rates of olfactory searching insects in relation to patches with increasing area and increasing density of host plants. The experiments (Paper II) and meta-analyses (Paper III) showed that the observed immigration rates of olfactory searching insects was well predicted by the relative increase in plume length, as estimated from the electroantennogram measurements (Paper I, III). The importance of immigration rates, relative to the effect of emigration and local growth was also investigated for the Cionus weevils in natural S. nodosa patches (Paper IV). This study showed that the density-patch size relationships of the weevils during early season were predicted by the net scaling of emigration and immigration rates, and differences in density-patch size relationships between the two species could be explained by inter-specific differences in their emigration rates from small patches. In conclusion, this thesis shows that search behavior can be used to predict immigration rates and spatial distributions of insects, with implications for pest control, conservation ecology and general ecological theory.
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| 2. |
- König, Malin A. E., 1987-
(författare)
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Context dependency of plant – animal interactions
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The strength and direction of interactions between organisms vary spatially across the landscape. Traditionally, the focus has been on how trait variation affects the interactions between species. However, differences in abiotic and biotic environmental factors may also alter the distribution, phenology and behavior of the interacting species. To be able to understand why an interaction varies across the landscape, the effects of trait variation has to be separated from the effects of the environmental context. In this thesis, I try to separate the effects of context and trait differences on plant resistance against herbivory, through experimental and observational studies conducted with two cytotypes of the perennial herb Cardamine pratensis and its main herbivore, Anthocharis cardamines.The results show that differences in plant resistance against oviposition under controlled conditions were mainly mediated by flower size; larger flowers were more attractive to the female butterfly. However, among-populations differences in oviposition under natural conditions were not related to the resistance observed under controlled conditions, or to ploidy type, flowering phenology or plant size. Within populations under natural conditions the oviposition patterns by A. cardamines was affected by the plant traits plant size and flowering phenology.The result of this thesis shows that among-population differences in intensity of plant-herbivore interactions were caused by differences in environmental context rather than by herbivore preferences for any phenotypic plant traits, while host plant selection within population was based on plant traits. This suggests that biotic and biotic context can have important effects on the intensity of plant-herbivore interactions. Although genetic traits influenced the outcome of the interaction within populations, it was the environmental context of the populations that determined largely if the interaction took place or not.
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| 3. |
- Lönnell, Niklas, 1969-
(författare)
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Dispersal of bryophytes across landscapes
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Dispersal, especially long-distance dispersal, is an important component in many disciplines within biology. Many species are passively dispersed by wind, not least spore-dispersed organisms.In this thesis I investigated the dispersal capacity of bryophytes by studying the colonization patterns from local scales (100 m) to landscape scales (20 km). The dispersal distances were measured from a known source (up to 600 m away) or inferred from a connectivity measure (1–20 km). I introduced acidic clay to measure the colonization rates over one season of a pioneer moss, Discelium nudum (I–III). I also investigated which vascular plants and bryophytes that had colonized limed mires approximately 20–30 years after the first disturbance (IV).Discelium effectively colonized new disturbed substrates over one season. Most spores were deposited up to 50 meters from a source but the relationship between local colonization rates and connectivity increased with distance up to 20 km (I–III). Also calcicolous wetland bryophyte species were good colonizers over similar distances, while vascular plants in the same environment colonized less frequently. Common bryophytes that produce spores frequently were more effective colonizers, while no effect of spore size was detected (IV). A mechanistic model that take into account meteorological parameters to simulate the trajectories for spores of Discelium nudum fitted rather well to the observed colonization pattern, especially if spore release thresholds in wind variation and humidity were accounted for (III).This thesis conclude that bryophytes in open habitats can disperse effectively across landscapes given that the regional spore source is large enough (i.e. are common in the region and produce spores abundantly). For spore-dispersed organisms in open landscapes I suggest that it is often the colonization phase and not the transport that is the main bottle-neck for maintaining populations across landscapes.
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| 4. |
- Marteinsdóttir, Bryndís, 1980-
(författare)
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Plant community assembly in grazed grasslands
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Species assembly into local communities from the surrounding region can be caused either by species failure to reach the site (i.e. seed limitation) or to establish (i.e. establishment limitation). The aim of this thesis was to investigate plant species assembly and to determine the relative importance of different factors in that process.In a cultivated landscape in southeast Sweden, plant community assembly was studied in grazed ex-arable fields. Community assembly from the surrounding region into the local community was explored using trait-based null models and seed sowing and transplanting experiments. The influence of local environmental factors and landscape history and structure on community assembly was also studied. In addition, differences in species assembly between ex-arable fields and semi-natural grasslands were explored.Seed limitation was the strongest filter on local community assembly. Only a fraction (36%) of species in a region dispersed to a local site and adding seeds/transplants increased species establishment. Species abundance at the regional scale, species dispersal method and seed mass strongly influenced which species arrived at the local sites. Establishment limitation also affected the assembly. Of species arriving at a site 78% did establish, seedling survival was low and which species established was influenced by species interactions, local environmental conditions and stochastic events. In addition, landscape structure that determined the species richness in the regional species pool influenced the local assembly. The comparison between assembly in ex-arable fields and semi-natural grasslands indicated that the main cause of difference in species assembly between them was difference in their age.The main conclusion of this thesis is that regional processes are more important than local factors in determining plant community assembly.
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| 5. |
- von Euler, Tove, 1976-
(författare)
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Environmental heterogeneity, population dynamics and life-history differentiation in Primula farinosa
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Allocation to reproduction is a key life-history trait. Optimal allocation to reproduction depends on environmental conditions because of their effects both on costs and benefits of reproduction and on patterns of growth, fecundity, and mortality. In this thesis, I studied 24 populations of the perennial herb Primula farinosa in the northern part of the Great Alvar on Öland, SE Sweden, and in an experimental garden at Stockholm University to investigate how plant allocation patterns and population dynamics vary along environmental gradients. In the first study, I performed experimental manipulations of reproduction to study costs of reproduction in relation to water availability. In the second study, I performed a demographic survey to investigate the effects of pre-dispersal seed predation on host-plant population dynamics in relation to environmental context. In the third study, I used a common garden experiment to investigate whether environmental variation among natural populations was correlated with genetic differentiation in reproductive effort, and in the fourth study, I performed reciprocal transplantations among four populations to investigate whether genetically based adaptive differentiation among local populations could be detected. The results showed that under natural conditions, plant reproductive costs, intensity of pre-dispersal seed predation, population growth rate and reproductive effort varied with water availability and vegetation height. Costs of reproduction were detected at high and low water availability but not under intermediate soil moisture conditions (paper I). Population dynamics of P. farinosa were affected by environmental conditions both directly, through effects on potential population growth rate (in the absence of seed predation) and indirectly, through effects on seed predation intensity and sensitivity to seed predation (paper II). Among-population genetic differentiation in reproductive allocation was documented in the common-garden experiment (paper III). However, reciprocal transplantations among populations separated by up to 6.2 km provided no evidence of local adaptation to current environmental conditions. Moreover, large differences in the performance of individuals transplanted to different study sites suggest that the study populations display considerable phenotypic plasticity (paper IV). Taken together, the results of these studies suggest that environmental variation has important direct and indirect effects on population dynamics and life history trade-offs in P. farinosa, and that differences in reproductive effort partly reflect genetic differentiation, but that phenotypic variation observed among natural populations does not reflect adaptations to current environmental conditions.
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