| 1. |
- Arnell, Matilda, 1987-
(författare)
-
Distribution patterns of fleshy-fruited woody plants at local and regional scales
- 2022
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Fleshy-fruited woody plants share a long history with humans, providing us with food and wood material. Because of this relation, we have actively moved some of these plants across landscapes and continents. In Sweden, these species are often found in open and semi-open habitats such as forest edges, their fruits are most often dispersed by birds and their flowers are, with some exceptions, pollinated by insects. In this thesis my overall aim was to map and analyse distribution patterns of fleshy-fruited woody plants in Sweden to expand our knowledge on the mechanisms governing their distributions. First, I mapped a population of the early flowering, fleshy-fruited shrub Daphne mezereum (common mezeron, tibast) and surveyed the reproduction and fruit removal of all individuals (chapter I). My main aim was to investigate to what extent reproduction and fruit removal was affected by local distribution patterns. Secondly, I mapped local distribution patterns of fleshy-fruited woody species and analysed spatial associations between life stages and species (chapter II). My main aim was to relate these spatial associations to predictions of how bird dispersal would shape the local distribution patterns and the hypothesis that birds create ‘wild orchards’. Thirdly, I digitized historical maps and surveyed fleshy-fruited woody species along transects across landscapes (chapter III). My aim was to examine the hypothesis that these species accumulate in open and semi open habitats created by human land use. Fourthly, I estimated range filling of woody plants in Sweden at a 1 km2 resolution (chapter IV). My aim was to compare these estimates among species with different dispersal systems to understand the effect of dispersal on the occupancy of woody species at regional scales.I found the distribution patterns of these species to be affected by past and present land use, supporting the hypothesis that these plants accumulate in open habitats. Occurrences of species in this guild in todays’ forest are positively related to past human land use (chapter III) and the density of D. mezereum increases with decreasing distances to forest edges (chapter I). This accumulation may in part be explained by the positive effect of forest edges on reproduction and fruit removal (chapter I). I further found local distribution patterns of this guild and the individual species to be aggregated (chapter I and II), and spatial associations between saplings and reproductive individuals to support the ‘orchard’ hypothesis (chapter II). The aggregated pattern of fruit-bearing individuals was positively related to fruit removal whereas aggregated flowering individuals was negatively related to fruit set (chapter I). On the regional scale, I found these species to occupy climatically suitable areas, or fill their potential ranges, to a less extent that wind dispersed trees and shrubs (chapter IV), which may indicate dispersal limitation.In conclusion, the behaviour of birds and humans have shaped, and still shape the current distribution of fleshy-fruited trees and shrubs in Sweden, resulting in accumulation in open habitats and locally aggregated distribution patterns. Changing land-use practices and potential mismatches between fruit maturation and bird dispersal with a changing climate may thus result in even lower chances of these species to fill their potential ranges, due to habitat losses and dispersal limitations at local and regional scales.
|
|
| 2. |
- Dahlberg, C. Johan, 1978-
(författare)
-
The role of microclimate for the performance and distribution of forest plants
- 2016
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Microclimatic gradients may have large influence on individual vital rates and population growth rates of species, and limit their distributions. Therefore, I focused on the influence of microclimate on individual performance and distribution of species. Further, I examined differences in how microclimate affect species with contrasting distributions or different ecophysiological traits, and populations within species. More specifically, I investigated the performance of northern and southern distributed forest bryophytes that were transplanted across microclimatic gradients, and the timing of vegetative and reproductive development among northern, marginal and more southern populations of a forest herb in a common garden. Also, I compared the landscape and continental distributions across forest bryophytes and vascular plants and, thus, their distribution limiting factors at different spatial scales. Lastly, I examined the population dynamics across microclimatic gradients of transplants from northern and southern populations of a forest moss. The effects of microclimatic conditions on performance differed among bryophytes with contrasting distributions. There were no clear differences between northern and southern populations in the timing of development of a forest herb or in the population dynamics of a moss. However, within each region there was a differentiation of the forest herb populations, related to variation in local climatic conditions and in the south also to proportion of deciduous trees. The continental distributions of species were reflected in their landscape distributions and vice versa, in terms of their occurrence optima for climatic variables. The variation in landscape climatic optima was, however, larger than predicted, which limit the precision for predictions of microrefugia. Probably, the distributions of vascular plants were more affected by temperature than the distributions of bryophytes. Bryophytes are sensitive to moisture conditions, which was demonstrated by a correlation between evaporation and the population growth rate of a forest moss. We might be able to predict species’ landscape scale distributions by linking microclimatic conditions to their population growth rates, via their vital rates, and infer larger scale distribution patterns.
|
|
| 3. |
- 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.
|
|
| 4. |
- Fogelström, Elsa, 1986-
(författare)
-
Plant phenology in seasonal environments
- 2019
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Phenology, or the seasonal timing life-history events such as emergence, reproduction and senescence will determine the outcome of interactions between plants and both abiotic and biotic aspects of the environment. Such timing is therefore of utmost importance for plants in seasonal environments. In this thesis, I first investigated the factors determining the start, end and length of the growing season for a perennial herb. Secondly, I estimated phenotypic selection on flowering time and investigated to which extent it corresponded to genotypic selection in a natural field setting. Thirdly, I estimated population differentiation in flowering time in a common garden and in the field. Lastly, I experimentally manipulated the synchrony of a perennial herb and its main herbivore to investigate the effects of herbivore phenological preference and plant-herbivore synchrony on the direction of selection on flowering time.I found that flowering individuals emerged earlier in spring than non-flowering individuals and that large individuals senesced later in autumn, suggesting that the length of the growing season is linked to individual condition and resource demands. Phenotypic selection favoured early-flowering individuals, but there was no genotypic selection. I found evidence for genetic population differentiation in flowering time in a common garden but not in the field. This suggests that, although flowering time has a genetic component, the observed variation in flowering time was mainly plastic under natural field conditions. Lastly, I show that constant herbivore preferences of plant phenology, in combination with environmentally driven variation in relative synchrony of the plant and the herbivore, leads to among-year variation in natural selection on flowering time. With this thesis, I contribute to identifying the factors affecting plant phenology as well as of the mechanisms shaping selection on flowering time in perennial plants. Such knowledge is essential for predicting species responses to climate change.
|
|
| 5. |
- Greiser, Caroline, 1987-
(författare)
-
Microclimate at range margins : Consequences for boreal forest understory species
- 2020
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A warmer climate will shift species distributional range margins poleward, but near-ground microclimates may modify these shifts. Cold-adapted northern species at their rear edge may survive locally in microrefugia with a colder microclimate, and warm-adapted southern species at their leading edge may colonize stepping stone habitats with a warmer microclimate. However, we do not always know if species ranges are limited by climate and which role microclimate variation plays in modifying range margins. This is especially true for lowland forests, where forest structure and composition have relatively large influences on near-ground microclimates.In this thesis, I explored patterns and drivers of forest microclimate at the southern margin of the boreal zone in central Sweden, where many northern and southern species meet. First, I measured, modelled and mapped near-ground temperatures across ca. 20 000 km2 of forested land (Paper I). Second, I tested if cold and warm microclimates favour northern and southern understory species, respectively. To answer this, I investigated the occurrence and performance patterns of understory vascular plants, bryophytes and lichens across microclimate gradients at the species’ northern or southern range margins (Paper II-IV). I performed both correlational analyses on natural populations and experimental testing with transplanted populations. Third, I derived recommendations and tools for biodiversity conservation and forest management (Paper I-IV).I found high spatial and temporal variation of forest microclimate, which was in the summer mainly linked to differences in forest density and in the cold season to terrain effects (Paper I). Cold and warm microclimates were occupied by natural edge populations of northern and southern species, respectively (Paper II and IV). However, in the transplant experiments with removed competition other factors were more important for the species performance. The southern herb appeared to cope well with the range of microclimate at its current northern range margin and instead seems to be limited by soil and light in northern conifer-dominated forests (Paper IV). The northern transplanted bryophytes and lichens showed no or a positive response to warmer temperature, but also to higher moisture, to more conifers in the overstory and to less gastropod grazing (Paper III). The results indicate that competition with southern species, herbivory, leaf litter and water scarcity might be more important than temperature as direct limiting factors at the species’ current southern range margin. To conclude, microclimate influences the occurrence and performance of range edge populations, but it likely does so indirectly via effects on water availability and biotic interactions.Forest management heavily modifies near-ground temperature and humidity and hence likely impacts the climate-driven range shifts of understory species. I call for considering these effects in conservation and management actions, e.g. by protecting valuable microclimates, moving from clear-cutting to selective logging, reducing forest fragmentation and drainage and favouring either broad-leaved or coniferous trees in the overstory - depending on the local conservation target (Paper I-IV). Climate-change induced biodiversity loss may thus be slowed down by responsible forest management that provides stepping stone habitats for advancing southern species as well as microrefugia for retreating northern species.
|
|
| 6. |
- Marteinsdóttir, Bryndís, 1980-
(författare)
-
Plant community assembly in grazed grasslands
- 2014
-
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.
|
|
| 7. |
- Nuppenau, Jan-Niklas, 1989-
(författare)
-
Thriving in extremes : Local adaptation of grasses (Poaceae) to geothermally heated soils on a subarctic island
- 2023
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Temperature is one of the most decisive parameters when it comes to determining characteristics and distributions of life worldwide. For plants, as sessile organisms, it is particularly important to be able to deal with the temperatures they are exposed to at a given location. To understand evolutionary processes in plants, it is therefore crucial to gain knowledge about how plants deal with extreme temperatures and respond to changes in temperature. Such knowledge is especially needed given the ongoing rise in temperature under climate change. However, investigations in natural systems on how plants cope with opposing temperature extremes and the effect of long term heating are scarce. In Iceland, a subarctic island in the North Atlantic, a limited number of plant species grow on geothermally heated soils and non-heated soils alike. This constitutes a fascinating natural laboratory for studying local adaptations to opposing temperature extremes and especially constant warming. In my thesis, I investigated responses to geothermal heating in three grass species: Agrostis stolonifera and Agrostis vinealis, which are among the few vascular plants growing on the most heated soils, and Festuca rubra, which grows on moderately heated soils.First, I reconstructed phylogenetic relationships among Icelandic populations of A. stolonifera and A. vinealis and accessions across both species distribution ranges (Paper I). For A. stolonifera, but not for A. vinealis, I found a distinct geothermal lineage, which is not the closest relative of non-thermal populations. In a subsequent test of thermal tolerance for the geothermal lineage of A. stolonifera, I found no difference in survival following cold treatment, but geothermal plants survived exposure to higher temperatures. However, geothermal plants overall performed worse at colder conditions, which indicates a trade-off between heat tolerance and performance at colder temperatures (Paper II). Comparing survival ability and flowering phenology of the geothermal and non-thermal lineages of A. stolonifera in an overwintering experiment, I found no differences in survival rates but delayed flowering in geothermal A. stolonifera (Paper III). I additionally compared winter survival ability and phenology among several geothermal and non-thermal populations of F. rubra, as well as between northern and southern Swedish populations. I found no difference between geothermal and non-thermal populations of F. rubra but delayed flowering and higher performance in the northern Swedish population (Paper IV).The different findings for different species and temperature conditions emphasize the complexities of plant evolutionary responses to elevated temperatures. Whether a species adapts to elevated temperatures seems to depend not only on the level of maximum temperature rise, but also on species’ evolutionary histories, and on winter conditions. The found trade-off between heat tolerance and performance at optimal conditions suggests that adapting to extreme heat may limit viability under cooler conditions. These findings highlight the peculiarities of geothermal ecosystems, their value for studying thermal tolerances and provide a framework for future work on thermal adaptations of geothermal grasses.
|
|
| 8. |
- Posledovich, Diana, 1984-
(författare)
-
Effects of climate on phenological synchrony between butterflies and their host plants
- 2015
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Shifts in species’ phenologies and phenological asynchronies between the interacting organisms have received a lot of attention in the context of climate change. Changes in temporal overlap between species, caused by phenological asynchrony, make species depending on one another become so separated in time that they can no longer interact. This may have important consequences both for single species, like fluctuations in abundances, and for the functioning of whole communities by creating mismatches between trophic levels and rearrangements of community structure. This thesis focuses on the impact of temperatures on spring timing and phenological synchrony in a herbivorous insect – host plant system, consisting of the orange tipbutterfly Anthocharis cardamines and five of its Brassicaceae host plant species. Paper I demonstrates that diapause duration and winter thermal conditions can determine the timing of spring emergence in the herbivore, and these traits may differ between species with different feeding strategies. In paper II we show that thermal reaction norms of post-winterdevelopment of A. cardamines display cogradient latitudinal variation.Paper III shows that temperature-mediated phenological plasticity of A. cardamines butterflies and a majority of the most used host plant species is similar within populations originating from different latitudes. Thus, the species’ timing appeared well conserved in response to thermal variation. In paper IV we explored the importance of the butterfly’s adult emergence and thermal conditions on the succeeding part of the butterfly’s life-cycle – larval development. The outcome from the interaction was examined for both the insect and the plant side. The degree in phenological overlap between the female butterflies and host plants as well as temperatures during larval development were found to influence larval development but had no effect on plant reproductive fitness. The four papers of the presented thesis demonstrate that developmental preadaptations, evolvedin a herbivore to maintain phenological synchrony with host plants across yearly variation of spring conditions, can prevent disruption of the interaction under a wide range of temperatures. This indicates that temporary constrained interactions are not always vulnerable to decoupling, particularly if they involve generalist strategy.
|
|
| 9. |
- 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.
|
|
| 10. |
- Bolinder, Kristina, 1987-
(författare)
-
Pollen and pollination in Ephedra (Gnetales)
- 2017
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Ephedra (Gnetales) is a gymnosperm genus with a long evolutionary history; the first dispersed pollen grains with affinity to the group are known already from the Permian. This thesis focuses on the evolutionary history of the group and different aspects of its pollination mechanisms. Despite the limited number of extant species of the genus (50-60), and a low morphological and genetic divergence among species, there is variation in pollination syndrome in the genus. The prevailing state in Ephedra, and most gymnosperms, is wind pollination. It is therefore surprising that one species, E. foeminea, is insect-pollinated. Together with co-workers I documented the pollination syndromes of E. foeminea and a sympatric species, E. distachya, based on long term field experiments in north-eastern Greece and aerodynamic investigations and calculations. Placing the results into an evolutionary framework reveals that the insect-pollinated species E. foeminea is sister to the remaining (mostly wind-pollinated) genus, and indicates that insect pollination is the ancestral state in the Gnetales. During the course of evolution of the group there has been a shift to wind pollination, which may have played a crucial role for the diversification of the crown group in the Paleogene. Pollination biology is often correlated with the morphology of the pollen such that pollen grains of anemophilous plants are small with a smooth surface, whereas pollen grains of entomophilous plants are larger with an ornamented surface and a covering of pollenkitt. The pollen morphology of Ephedra can be broadly divided into two types: an ancestral type with an unbranched pseudosulcus between each pair of plicae, and a derived type with a branched pseudosulcus between each pair of plicae. Further, the pollen morphology and ultrastructure of the pollen wall in Ephedra are to some degree correlated with the pollination syndrome and capability of long distance dispersal. Pollen of E. foeminea has a denser ultrastructure, as a result a higher settling velocity and is therefore capable of flying shorter distances than does pollen of the anemophilous E. distachya, and other investigated anemophilous species that show a more spacious ultrastructure of the pollen grain. These results can be useful in the reconstruction of the pollination mechanism of extinct taxa of the Ephedra-lineage in the future.
|
|
