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- König, Malin A. E., 1987-
(author)
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Context dependency of plant – animal interactions
- 2014
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Doctoral thesis (other academic/artistic)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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| 2. |
- Lönnell, Niklas, 1969-
(author)
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Dispersal of bryophytes across landscapes
- 2014
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Doctoral thesis (other academic/artistic)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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| 3. |
- Marteinsdóttir, Bryndís, 1980-
(author)
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Plant community assembly in grazed grasslands
- 2014
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Doctoral thesis (other academic/artistic)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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