| 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. |
- Arnell, Matilda, 1987-
(författare)
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Distribution patterns of fleshy-fruited woody plants at local and regional scales
- 2022
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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.
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| 3. |
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| 4. |
- Arnell, Matilda, 1987-, et al.
(författare)
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Reproductive success, fruit removal and local distribution patterns in the early-flowering shrub Daphne mezereum
- 2023
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Ingår i: Nordic Journal of Botany. - 0107-055X .- 1756-1051. ; :10
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Tidskriftsartikel (refereegranskat)abstract
- In insect-pollinated, bird-dispersed plants, both investment in reproduction and reproductive success involve interactions between plants and their pollinators and dispersers. The outcome of these plant–animal interactions may be affected by the number of flowers and fruits, as well as by the plants' local environment and by spatial associations among plants. In this study we mapped the spatial distribution of individuals in a population of the early flowering, fleshy-fruited shrub Daphne mezereum, in a forest in boreo-nemoral Sweden. For all mapped individuals we collected data on numbers of flowers and fruits and fruit removal, for three consecutive years. We analysed spatial associations among individuals, and the effects on reproductive performance and fruit removal of plant height, numbers of flowers and fruits, distance to forest edge, and neighbouring flower and fruit density. Our results show that the density of D. mezereum increases with increasing proximity to forest edge. The number of flowers produced, as well as fruit set and fruit removal, show the same positive relationship with increasing proximity to forest edges. We further show that individuals are aggregated up to distances of about 10 m. The flower production of neighbouring conspecific individuals within 10 m is negatively related to fruit set whereas the fruit production of neighbours is positively related to fruit removal. Our main conclusion is that the spatial distribution of D. mezereum affects reproductive success and fruit removal, which in turn has the potential to feed back to the spatial distribution pattern. Combining studies of reproduction with spatial analyses is important to advance our understanding of the dynamics of plant populations.
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| 5. |
- Arvanitis, Leena, et al.
(författare)
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Butterfly seed predation: effects of landscape characteristics, plant ploidy level and population structure
- 2007
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Ingår i: Oecologia. - : Springer Science and Business Media LLC. - 0029-8549 .- 1432-1939. ; 152:2, s. 275-285
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Tidskriftsartikel (refereegranskat)abstract
- Polyploidization has been suggested as one of the most common mechanisms for plant diversification. It is often associated with changes in several morphological, phenological and ecological plant traits, and therefore has the potential to alter insect–plant interactions. Nevertheless, studies evaluating the effect of plant polyploidy on interspecific interactions are still few. We investigated pre-dispersal seed predation by the butterfly Anthocharis cardamines in 195 populations of two ploidy levels of the herb Cardamine pratensis (tetraploid ssp. pratensis, 2n = 30 vs. octoploid ssp. paludosa, 2n = 56–64). We asked if differences in incidence and intensity of predation among populations were related to landscape characteristics, plant ploidy level and population structure. The incidence of the seed predator increased with increasing plant population size and decreasing distance to nearest population occupied by A. cardamines. The intensity of predation decreased with increasing plant population size and was not affected by isolation. Probability of attack decreased with increasing shading, and intensity of predation was higher in grazed than in non-grazed habitats. The attack intensity increased with increasing mean flower number of plant population, but was not affected by flowering phenology. Individuals in tetraploid populations suffered on average from higher levels of seed predation, had higher mean flower number, were less shaded and occurred more often in grazed habitats than octoploid populations. When accounting for differences in habitat preferences between ploidy levels there was no longer a difference in intensity of predation, suggesting that the observed differences in attack rates among populations of the two ploidy levels are mediated by the habitat. Overall, our results suggest that polyploidization is associated with differentiation in habitat preferences and phenotypic traits leading to differences in interspecific interaction among plant populations. This, in turn, may facilitate further divergence of ploidy levels.
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| 6. |
- Arvanitis, Leena, 1959-
(författare)
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Plant polyploidy and interactions with insect herbivores
- 2007
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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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| 7. |
- Bisang, Irene, et al.
(författare)
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Family affiliation, sex ratio and sporophyte frequency in unisexual mosses
- 2014
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Ingår i: Botanical journal of the Linnean Society. - : Oxford University Press (OUP). - 0024-4074 .- 1095-8339. ; 174:2, s. 163-172
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Tidskriftsartikel (refereegranskat)abstract
- Patterns of sex expression and sex ratios are key features of the life histories of organisms. Bryophytes are the only haploid-dominant land plants. In contrast with seed plants, more than half of bryophyte species are dioecious, with rare sexual expression and sporophyte formation and a commonly female-biased sex ratio. We asked whether variation in sex expression, sex ratio and sporophyte frequency in ten dioecious pleurocarpous wetland mosses of two different families was best explained by assuming that character states evolved: (1) in ancestors within the respective families or (2) at the species level as a response to recent habitat conditions. Lasso regression shrinkage identified relationships between family membership and sex ratio and sporophyte frequency, whereas environmental conditions were not correlated with any investigated reproductive trait. Sex ratio and sporophyte frequency were correlated with each other. Our results suggest that ancestry is more important than the current environment in explaining reproductive patterns at and above the species level in the studied wetland mosses, and that mechanisms controlling sex ratio and sporophyte frequency are phylogenetically conserved. Obviously, ancestry should be considered in the study of reproductive character state variation in plants.(c) 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 174, 163-172.
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| 8. |
- Bisang, Irene, et al.
(författare)
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Life history characteristics and historical factors are important to explain regional variation in reproductive traits and genetic diversity in perennial mosses
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Ingår i: Annals of Botany. - 0305-7364 .- 1095-8290.
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Tidskriftsartikel (refereegranskat)abstract
- Background and aims Plants have evolved an unrivalled diversity of reproductive strategies, including variation in the degree of sexual versus clonal reproduction. This variation has important effects on the dynamics and genetic structure of populations. We examined the association between large-scale variation in reproductive patterns and intraspecific genetic diversity in two moss species where sex is manifested in the dominant haploid generation and sex expression is irregular. We predicted that in regions with more frequent realised sexual reproduction, populations should display less skewed sex ratios, more often express sex, and have higher genetic diversity than in regions with largely clonal reproduction.Methods We assessed reproductive status and phenotypic sex in the dioicous long-lived Drepanocladus trifarius and D. turgescens, in 248 and 438 samples across two regions in Scandinavia with frequent or rare, respectively, realised sexual reproduction. In subsets of the samples, we analysed genetic diversity using nuclear and plastid sequence information and identified sex with a sex-specific molecular marker in non-reproductive samples.Key results Contrary to our predictions, sex ratios did not differ between regions, genetic diversity did not differ in D. trifarius and was higher in the region with rare sexual reproduction in D. turgescens. Supporting our predictions, relatively more samples expressed sex in D. trifarius in the region with frequent sexual reproduction. Overall, samples were mostly female. Degree of sex expression and genetic diversity differed between sexes.Conclusions Sex expression levels, regional sex ratios and genetic diversity were not directly associated with regional frequency of realised sexual reproduction, and relationships and variation patterns differed between species. We conclude that a combination of species-specific life histories such as longevity, overall degree of successful sexual reproduction and recruitment, and historic factors, are important to explain this variation. Our data on haploid-dominated plants significantly complement plant reproductive biology.
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| 9. |
- Bisang, Irene, et al.
(författare)
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No evidence of sexual niche partitioning in a dioecious moss with raresexual reproduction
- 2015
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Ingår i: Annals of Botany. - : Oxford University Press (OUP). - 0305-7364 .- 1095-8290.
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Tidskriftsartikel (refereegranskat)abstract
- Background and Aims. Roughly half of the species of bryophytes have separate sexes (dioecious) and half are hermaphroditic (monoecious). This variation has major consequences for the ecology and evolution of the different species. In some sexually reproducing dioecious bryophytes, sex ratio has been shown to vary with environmental conditions. This study focuses on the dioecious wetland moss Drepanocladus trifarius, which rarely produces sexual branches or sporophytes and lacks apparent secondary sex characteristics, and examines whether genetic sexes exhibit different habitat preferences, i.e. whether sexual niche partitioning occurs.Methods. A total of 277 shoots of D. trifarius were randomly sampled at 214 locations and 12 environmental factors were quantified at each site. Sex was assigned to the individual shoots collected in the natural environments, regardless of their reproductive status, using a specifically designed molecular marker associated with female sex.Key Results. Male and female shoots did not differ in shoot biomass, the sexes were randomly distributed with respect to each other, and environmental conditions at male and female sampling locations did not differ. Collectively, this demonstrates a lack of sexual niche segregation. Adult genetic sex ratio was female-biased, with 28 females for every male individual.Conclusions. The results show that although the sexes of D. trifarius did not differ with regard to annual growth, spatial distribution or habitat requirements, the genetic sex ratio as nevertheless significantly female-biased. This supports the notion that factors other than sex-related differences in reproductive costs and sexual dimorphism can also drive the evolution of biased sex ratios in plants
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