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  • 251.
    Hambäck, Peter
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Andersson, Petter
    Stockholm University, Faculty of Science, Department of Botany.
    Bukovinszky, Tibor
    Netherlands Institute of Ecology.
    Trait-mediated effects modify patch-size density relationships in insect herbivores and parasitoids2012In: Trait-mediated indirect interactions:  Ecological and evolutionary perspecitves / [ed] T. Ohgushi, O.J. Schmitz and R.D. Holt, Cambridge, UK: Cambridge University Press, 2012, p. 466-488Chapter in book (Refereed)
  • 252.
    Hambäck, Peter
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Bergman, K-O
    Bommarco, R
    Krauss, J
    Kuussarri, M
    Pöyry, J
    Öckinger, E
    Allometric density responses in butterflies: The response to small and large patches by small and large species.2010In: Ecography, ISSN 0906-7590, E-ISSN 1600-0587, Vol. 33, p. 1149-1156Article in journal (Refereed)
  • 253.
    Hambäck, Peter
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Björkman, Maria
    Stockholm University, Faculty of Science, Department of Botany.
    Rämert, Birgitta
    Hopkins, Richard
    Scale-dependent responses in cabbage herbivores affect attack rates in spatially heterogenous systems2009In: Basic and Applied Ecology, ISSN 1439-1791, E-ISSN 1618-0089, Vol. 10, p. 228-236Article in journal (Refereed)
    Abstract [en]

    Herbivorous insects face a dilemma when selecting suitable hosts in a complex environment, and their sensory capability may often reduce the female capacity for proper selection. As a consequence, eggs are often deposited on inferior hosts, affecting both insect and host plant fitness. We examined the attack rates of three cabbage herbivores in monocultures and biculture plots of different Brassica oleracea genotypes, with different spatial heterogeneity. The main goals of the study were to improve our understanding of the spatial scales involved in herbivore search processes and to examine the possibility of using spatial heterogeneity for manipulating pest attack rates in cabbage cropping systems. The results showed that the host selection behaviour of the small white butterfly (Pieris rapae) was strongly dependent on spatial heterogeneity. The difference in egg density between plant genotypes was larger when contrasting plants were growing in close proximity than in monoculture. This suggests that P. rapae is able to differentiate among genotypes from a small distance, while selection is compromised at larger spatial scales. The two other herbivores in the study (Mamestra brassicae and Delia radicum) did not respond to heterogeneity at any spatial scale, but showed a constant preference hierarchy. This suggests that host selection in these species occurs after direct plant contact. The difference in species’ responses to spatial heterogeneity has consequences both for selection gradients in natural communities and for the potential to reduce pest attack in polyculture systems.

  • 254.
    Hambäck, Peter
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Gilbert, James
    Schneider, Katie
    Martinson, Holly
    Kolb, Gundula
    Stockholm University, Faculty of Science, Department of Botany.
    Fagan, William
    Effects of body size, trophic mode and larval habitat on Diptera stoichiometry: a regional comparison2009In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 118, p. 615-623Article in journal (Refereed)
    Abstract [en]

    Ecological stoichiometry has emerged as a tool for exploring nutrient demand and evolutionary responses to nutrient limitation. Previous studies of insects have found predictable variability in stoichiometry, both in relation to body size and trophic mode, at ordinal levels or higher. Our study further examines the evolutionary and ecological lability in these traits by comparing the effects of body size, trophic mode (larval and adult) and larval habitat on the stoichiometry of insects within one order (Diptera). The study also expands on previous work by analyzing trophic mode both at coarse (detritivore, herbivore, predator) and fine (high- vs low- nutrient quality resources within trophic categories) scales and by comparing nutrient stoichiometry in two geographical regions, Sweden and Arizona. As predicted, adults feeding on nectar or pollen had the lowest body N content in the dataset. Additionally, for Diptera with predatory larvae, species low N diets had lower body N content than those with high N diets. However, body N content was not consistently lower for all species with low N resources, as species feeding on plant material were indistinguishable in stoichiometry from predators with high N diets. We suggest that these results emerge because larval resource exploitation is poorly understood in herbivorous Diptera species. Body P content for Swedish Diptera decreased with body size for all trophic modes, and the only difference among trophic modes was that blood feeders had higher P content than other groups. The regional comparison further showed that the allometry of body P content is a labile trait that may vary at regional scales, as there was no allometric scaling of body P content in the Arizona data set, in contrast to the Swedish data set. These results are not easily explained by existing theoretical frameworks, but instead point to a general context-dependence of P stoichiometry, which should now be a focus for future work.

  • 255. Hambäck, Peter
    et al.
    Oksanen, Lauri
    Ekerholm, Per
    Lindgren, Åsa
    Stockholm University, Faculty of Science, Department of Botany.
    Oksanen, Tarja
    Schneider, Michael
    Predators indirectly protect tundra plants by reducing herbivore abundance2004In: Oikos, ISSN 0030-1299, Vol. 106, no 1, p. 85-92Article in journal (Refereed)
  • 256.
    Hambäck, Peter
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Summerville, Keith
    Steffen-Dewenter, Ingolf
    Krauss, Jochen
    Englund, Göran
    Crist, Thomas
    Habitat specialisation, body-size and family identity explain Lepidopteran density-area relationships in a cross-continental comparison.2007In: Proceedings of the National Academy of Sciences of the United States of America, Vol. 104, p. 8368-8373Article in journal (Refereed)
    Abstract [en]

    Habitat fragmentation may strongly affect species density, species interactions and the rate of ecosystem processes. It is therefore important to understand the observed variability among species responses to fragmentation, and the underlying mechanisms. In this study, we compare density-area relationships (DAR) for 344 lepidopteran species belonging to 22 families (butterflies and moths). This analysis suggested that the DARslope is generally positive for moths and negative for butterflies. The differences are suggested to occur because moths are largely olfactory searchers, whereas most butterflies are visual searchers. The analysis also suggests that DARs vary as a function of habitat specialisation and body size. In butterflies, generalist species had a more negative DARslope than specialist species because of a lower patch size threshold. In moths, the differences in DARslope between forest and open habitat species were large for small species but absent for large species. This is argued to occur because the DARslope in large species mainly reflect their search mode, which does not necessarily vary between moth groups, whereas the slope in small species reflect population growth rates.

  • 257.
    Hambäck, Peter
    et al.
    Stockholm University, Faculty of Science, Department of Botany. Växtekologi.
    Vogt, MajBritt
    Tscharntke, Teja
    Thies, Carsten
    Englund, Göran
    Top-down and bottom-up effects on the spatiotemporal dynamics of cereal aphids: testing scaling theory for local density2007In: Oikos, Vol. 116, p. 1995-2006Article in journal (Refereed)
    Abstract [en]

    The relationship between density and area depends on local growth rates and the area-dependence of migration rates. These rates vary among taxa due to dispersal behaviour, plot productivity and natural enemy impact. Previous studies in aphids suggest that aphid densities are highest in patches of intermediate sizes, and lower in small and large patches. The suggested mechanism causing these patterns is that the dispersal behaviour in aphids creates a mixture of area- and perimeter-dependent migration rates. In this paper, we used these predictions to examine the additional consequences of nutrient availability and natural enemies on the densityarea

    relationship. The derived predictions were compared to data from a system with three aphid species, a set of aphid parasitoids and generalist natural enemies, and at two levels of plant nutrient availability. We find that predictions from the model based only on dispersal and local growth agree with the temporal dynamics of

    density-area relationships for aphids in high nutrient patches. In patches with low nutrients, high parasitism rates appeared to cause a negative density-area relationship for aphids, thereby deviating from predictions driven by the aphids’ dispersal behavior. Hence, the dispersal model with scale-dependent migration rates can provide a useful tool for understanding insect distribution in patch size gradients, but the relative importance of top-down effects can completely change with plot productivity.

  • 258.
    Hamisi, Mariam
    Stockholm University, Faculty of Science, Department of Botany.
    Genetic variability and nitrogenase activity of cyanobacterial communities associated with tropical seagrass meadows (western Indian Ocean)2010Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Tropical seagrass ecosystems are highly productive and important for sustaining marine life and associated coastal societies. In this study, the diversity and role of nitrogen-fixing cyanobacteria associated with five common seagrass genera in coastal regions of the western Indian Ocean (WIO; Tanzania) were examined, as well as the impact of anthropogenic activities. Cyanobacteria were characterized morphologically and genetically (16S rRNA and nifH gene phylogeny), as were diel variations in nifH gene expression, NifH protein levels and nitrogenase activity. The results revealed that WIO seagrass beds supported rich cyanobacterial diversity and that these represented approx. 83% of total clones obtained (DNA and RNA nifH clone libraries). Non-heterocystous genera, such as Oscillatoria, Lyngbya, Leptolyngbya, Phormidium and Microcoleus dominated, while heterocystous morphotypes such as Calothrix were less frequent and unicellular morphotypes (e.g. Gloeocapsa, Chroococcus and Chroococcidiopsis) were few. Additionally, the phylogenetic analysis revealed several novel uncharacterized cyanobacterial clades. Cyanobacterial composition and nitrogenase activity varied over seasons and between the seagrass species. Day time nitrogenase activity originated primarily from heterocystous phylotypes, while non-heterocystous filamentous phylotypes fixed nitrogen at night. The highest activity in the diel cycle was 358 ± 232 nmol C2H4 g-1 h-1at 09.00 associated with epiphytes of the seagrass Cymodocea. Nitrogenase activity was consistently lower in anthropogenically disturbed (eutrophication) seagrass sites. Such data suggest that diazotrophic cyanobacteria may be a significant source of ‘new’ nitrogen in the often oligotrophic coastal regions of tropical oceans. It is also proposed that the rapid shifts in the cyanobacterial population and function found may also be used as early disturbance indicator in coastal management practices.

  • 259.
    Hamisi, Mariam
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Díez, Beatriz
    Institut de Ciéncies del Mar (ICM), CMIMA-CSIC, Barcelona.
    Lyimo, Thomas
    University of Dar es Salaam, Tanzania.
    Ininbergs, Karolina
    Stockholm University, Faculty of Science, Department of Botany.
    Bergman, Birgitta
    Stockholm University, Faculty of Science, Department of Botany.
    Cyanobacteria associated with the phyllosphere of the seagrass Cymodocea rotundata: Diversity, diel nifH expression and nitrogenase activity: Diversity, nifH expression and activity in seagrassManuscript (preprint) (Other academic)
    Abstract [en]

    Tropical seagrass ecosystems are highly productive and extremely important for sustaining marine life. As seagrasses are associated with complex assemblages of poorly examined epiphytic microbes, we proposed that nitrogen-fixing microorganisms may contribute to the productivity. The morphological and genetic diversity (based on the 16S rRNA and nifH genes) of cyanobacteria and diel variations in nifH gene expression, NifH protein levels and nitrogenase (nitrogen-fixing) activity were examined in the phyllosphere of Cymodocea rotundata of coastal areas of the western Indian Ocean (Tanzania). The 16S rRNA and nifH gene analyses during two consecutive years (October-November, 2007 and 2008) revealed the dominance of a mixed cyanobacterial community. Most sequences represented free-living uncultured cyanobacteria previously reported as benthic in the region, clearly separated from marine planktonic phylotypes, while a few sequences clustered with cyanobacterial symbionts of diatoms. Appreciable, but varying nitrogenase activities were found on a diel as well as monthly basis, with the highest activity encountered, 358 ± 232 and 258 ± 139 nmol C2H4 g-1 h-1, in November. On a diel basis, nifH gene expression coincided with the NifH protein level (Oct 2008) and nitrogenase activity. At day time, nifH gene expression primarily originated from heterocystous phylotypes, while from non-heterocystous filamentous phylotypes (mainly Oscillatoriales) at night. The data suggest that a variety of diazotrophic cyanobacteria are common among the epiphytes on Cymodocea and we propose that these may represent a valuable source of ‘new’ nitrogen in the often oligotrophic, but ecologically important seagrass ecosystems.

  • 260.
    Hamisi, Mariam I.
    et al.
    University of Dodoma, School of Natural Sciences and Mathematics.
    Mvungi, Esther F.
    Stockholm University, Faculty of Science, Department of Botany.
    Lyimo, Thomas J.
    University of Dar es Salaam, Department of Molecular Biology and Biotechnology.
    Mamboya, Florence A.
    Dar es Salaam Institute of Technology, Department of Sciences and Laboratory Technology.
    Österlund, Katrin
    Stockholm University, Faculty of Science, Department of Botany.
    Bergman, Birgitta
    Stockholm University, Faculty of Science, Department of Botany.
    Björk, Mats
    Stockholm University, Faculty of Science, Department of Botany.
    Díez, Beatriz
    Institut de Ciéncies del Mar (ICM), CMIMA-CSIC, Barcelona.
    Nutrient enrichment affects the seagrass Cymodocea serrulata and induces changes to its epiphytic cyanobacterial communityManuscript (preprint) (Other academic)
    Abstract [en]

    To better understand how elevated water column nutrient levels affect the performance of the seagrass Cymodocea serrulata as well as the composition and density of its associated epiphytes, two sets of experiments were carried out where nutrient concentration were manipulated in a flow though system containing seagrasses. The photosynthetic performance, growth characteristics and nutrient content (N:P) were followed for C. serrulata. Simultaneously the biomass, species composition for the epiphytic cyanobacteria, in particular diazotrophs was monitored. The photosynthetic capacity of seagrasses decreased with increase in nutrient concentrations and exposure time. Nutrient contents of seagrass leaves and epiphytes decreased after nutrient addition. A higher diversity of both heterocystous and non-heterocystous cyanobacteria was observed in the experimental seagrasses as compared with natural field samples. Many of the cyanobacterial sequences retrieved represented uncultured and potentially novel diazotrophic phylotypes. Diel nitrogenase activity measurements verified the presence of a distinct proportion of diazotrophs, which was negatively affected by moderate nutrient levels. These results demonstrate that seagrasses were physiologically stressed by the increased nutrient level as revealed by low maximum quantum yields, although the effect was not instant. In contrast the epiphytes whose response was apparent during the short term exposure to moderate nutrient concentration which also promoted rapid change in their composition.

  • 261.
    Hamisi, Mariam
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Lyimo, Thomas
    University of Dar es Salaam, Tanzania.
    Cyanobacteria Occurrence and Nitrogen Fixation Ratesin the Seagrass Meadows of the East Coast of Zanzibar: Comparisons of Sites With and Without Seaweed Farms2008In: Western Indian Ocean journal of marine science, ISSN 0856-860X, Vol. 7, no 1, p. 45-55Article in journal (Refereed)
    Abstract [en]

    The occurrence and biological nitrogen fixation rates of epiphytic and benthic diazotrophs were studied in seagrass meadows at sites with seaweed farms and at a control site without seaweed farms from two locations, Chwaka Bay and Jambiani, along the east coast of Zanzibar. Ten species of cyanobacteria were encountered and Lyngbya majuscula and Microcoleus sp. were dominant in Chwaka Bay and Jambiani respectively. Cyanobacterial occurrence was significantly higher in seagrass meadows without seaweed farms (P<0.02), but there was no significant difference (P>0.05) in biomass (chlorophyll a). Biomass averaged 2.96±0.73 and 3.10±1.24 μg Chl a cm-2 in seaweed farms and 3.46±1.72 μg Chl a cm-2 at Chwaka Bay and 3.14±1.31 μg Chl a cm-2 at Jambiani in transects without seaweed farms. Nitrogenase activity showed no significant differences between sites with and without seaweed farms, (P=0.66 Chwaka and 0.75 at Jambiani). Fixation rates in sites without seaweed farms averaged 35.8±39.9 (Chwaka Bay) and 13.1±12.7 (Jambiani) μmol of C2H4 produced/m2/hr, while with seaweed farms averaged 22.6±22.5 and 12.8±14.9 μmol C2H4 produced/m2/hr at the same sites. There were no significant differences in nutrient levels between locations, sites with and without seaweed farms, or between tidal levels except for nitrate, which was significantly higher (P=0.01) at Jambiani than at Chwaka Bay. It was concluded that diazotrophs contribute a significant amount of exogenous nitrogen to the seagrass ecosystem, but no significant differences could be found between sites with or without seaweed farms.

  • 262.
    Hamisi, Mariam
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Lyimo, Thomas
    University of Dar es Salaam.
    Díez, Beatriz
    Institut de Ciéncies del Mar (ICM), CMIMA-CSIC, Barcelona.
    Björk, Mats
    Stockholm University, Faculty of Science, Department of Botany.
    Mvungi, Esther
    Stockholm University, Faculty of Science, Department of Botany.
    Mamboya, Florence
    Dar es Salaam Institute of Technology.
    Changes in the epiphytic cyanobacterial community and diazotrophic activity on the tropical seagrasses induced by varying nutrient regimesManuscript (preprint) (Other academic)
    Abstract [en]

    Seagrasses were subject to different nitrogen (N) and phosphorus (P) regimes in a flow trough system (four weeks) to study the influence of moderate nutrient enrichments on the associated cyanobacterial diversity and diazotrophic activity. The seagrass Cymodocea serrulata (R. Brown) were collected outside an urbanized area, west of the Unguja Island, Zanzibar in the Indian Ocean. The epiphytic cyanobacterial community was characterized morphologically (light microscopy) and phylogenetically by DGGE fingerprinting using the 16S rRNA and nifH genes. A lower diversity of both heterocystous and non-heterocystous cyanobacteria was apparent in the natural seagrass stands, when compare to the pulsed nutrient additions that stimulated the growth of the cyanobacterial epiphytes. Non-heterocystous morpho- and genotypes (e.g. Lyngbya, Oscillatoria and Leptolyngbya) dominated and were intermixed with a few representatives of the heterocystous genus Calothrix. Many of the cyanobacterial sequences retrieved represented uncultured and potentially novel diazotrophic phylotypes. Diel nifH gene transcription levels and patterns, and the diel nitrogenase activity (acetylene reduction; max levels of 70.1 ±.19 nmol C2H4 g-1 h-1) verified the presence of a distinct proportion of diazotrophs, which however was negatively affected even by moderate nutrient additions. Although the seagrass host remained unaffected, the increased nutrients levels, mimicking anthropogenic eutrophication in these coastal regions, promoted a rapid change in the epiphytic community composition

  • 263.
    Hamisi, Mariam
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Lyimo, Thomas
    University of Dar es Salaam, Tanzania.
    Muruke, Masoud
    University of Dar es Salaam, Tanzania.
    Bergman, Birgitta
    Stockholm University, Faculty of Science, Department of Botany.
    Nitrogen fixation by epiphytic and epibenthic diazotrophs associated with seagrass meadows along the Tanzanian coast, Western Indian Ocean2009In: Aquatic Microbial Ecology, ISSN 0948-3055, E-ISSN 1616-1564, Vol. 57, p. 33-42Article in journal (Refereed)
    Abstract [en]

    Seasonal, diurnal, and age-dependent variations in nitrogen fixation (nitrogenase activity) by epiphytic diazotrophs colonizing the seagrasses Halodule uninervis, Cymodocea rotundata, Thalassodendron ciliatum, and Thalassia hemprichii, and by epibenthic diazotrophs associated with seagrass-vegetated and nonvegetated sediments, were estimated at 2 sites along the Tanzanian coast, Western Indian Ocean. Acetylene reduction-gas chromatography showed that nitrogenase activity values were significantly higher (p = 0.0004) at the site with low nutrient levels (Mjimwema) than at the site with higher nutrient levels (Ocean Road). The nitrogenase activity ranged from 10 to 192 nmol N g–1 h–1 for H. uninervis, 7 to 80 nmol N g–1 h–1 for C. rotundata, 10 to 75 nmol N g–1 h–1 for Thalassia hemprichii, and from 4 to 61 nmol N g–1 h–1 for Thalassodendron ciliatum. Nitrogenase activity values in sediments covered by seagrasses were significantly higher than in surrounding nonvegetated sediments (t = 4.021, p = 0.0005). Significant variations in nitrogenase activity were apparent depending on leaf age and season, with highest activity being found in mid-aged leaves during the northeastern monsoon (NEM), and in older leaves during the southeastern monsoon (SEM). Daytime nitrogenase activity was appreciable on above-ground seagrass parts, while rhizosphere activity peaked at night-time. Collectively our data show that diazotrophs (cyanobacteria and other bacteria) are associated with seagrasses (leaves and roots), and potentially constitute an integral part of the ecosystem. They show highly dynamic nitrogenase activity and a succession in seagrass colonization, and we concluded that their presence may contribute to the productivity of the seagrass beds.

  • 264.
    Hansen, Joakim
    Stockholm University, Faculty of Science, Department of Botany.
    Distribution patterns of macroinvertebrates in vegetated shallow soft-bottom bays of the Baltic Sea2007Licentiate thesis, monograph (Other academic)
  • 265.
    Hansen, Joakim
    Stockholm University, Faculty of Science, Department of Botany.
    Effects of morphometric isolation and vegetation on the macroinvertebrate community in shallow Baltic Sea land-uplift bays2010Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Shallow sheltered Baltic Sea bays are ecologically important habitats that harbour a unique vegetation community and constitute vital reproduction areas for many coastal fish species. Knowledge about the invertebrate community in these bays is, however, limited. This thesis examines the macroinvertebrate community in shallow sheltered Baltic Sea bays and how it is affected by: (1) the natural morphometric isolation of bays from the sea due to post-glacial land uplift; and (2) differences in vegetation types. The invertebrate biomass and number of taxa was found to decrease with increased bay isolation. The taxon composition changed from dominance by bivalves and gastropods in open bays to a community composed of a larger proportion of insects in isolated bays. Stable isotope analysis indicated epiphytes and periphyton as the major energy resources for most of the examined consumers, but the relative importance of these in relation to larger plants decreased for some consumers with increased bay isolation. A comparison of invertebrate abundance between plants revealed a close relationship with morphological complexity of the plants. More complexly structured plants had higher invertebrate abundance than plants with simpler morphology. The results suggest that management of these coastal habitats should be dynamic and take into consideration the natural change in invertebrate community resulting from the slow bay isolation process. In addition, the results imply that changes in the aquatic vegetation due to anthropogenic influences could induce changes in the invertebrate community as the plant habitat structure is altered. A changed invertebrate community may in turn affect higher trophic levels since invertebrates are important food for many fish and waterfowl species.

  • 266.
    Hansen, Joakim
    Stockholm University, Faculty of Science, Department of Botany.
    The role of submersed angiosperms and charophytes for aquatic fauna communities2007Book (Other academic)
  • 267.
    Hansen, Joakim
    et al.
    Stockholm University, Faculty of Science, Department of Botany. Avd. för växtekologi.
    Johansson, Gustav
    Johan.
    Grunda havsvikar längs Sveriges kust: Mellanårsvariationer i undervattensvegetation och fiskyngelförekomst2008Report (Other academic)
    Abstract [sv]

    Sammanfattning.

    I föreliggande studie undersöktes mellanårsvariationer i vattenvegetations- och fiskyngelsamhällen

    i grunda havsvikar längs den svenska östersjökusten. Syftet med studien var att ta fram

    riktlinjer för uppföljningsintervaller inom miljöövervakning av dessa miljöer. Variationer i

    vegetations- och fisksamhällena undersöktes även med hänsyn till faktorer som beskriver vikarnas

    geografiska läge, form och öppenhet mot havet. Inventeringar av vegetation och fiskyngel

    utfördes från slutet av juli till september i Västerbottens, Gävleborgs, Uppsala, Stockholms,

    Östergötlands, Kalmar, Blekinge och Skåne län. I denna studie analyserades 50 vikar

    med avseende på vegetation och 41 vikar med avseende på fiskyngel.

    Resultaten visade att täckningsgraden av stora vattenväxter och trådformiga alger varierade

    mycket mellan åren. Artsammansättningen av vegetation var relativt likartad i vikarna

    mellan åren, men i vissa vikar, främst inneslutna, varierade artsammansättningen mycket. Det

    förekom ingen samstämmig mellanårsvariation i växtartsammansättning i de grunda vikarna,

    d.v.s. förekomsten av arter var inte likartat hög eller låg i flera vikar samma år. En betydande

    del av skillnaderna i växtartsammansättning mellan vikarna kunde förklaras av skillnader i

    latitud och vikarnas öppenhet mot havet.

    Artsammansättningen av fiskyngel i vikarna varierade kraftigt mellan åren. Resultaten

    visade även en samstämmig mellanårsvariation av årsyngelsammansättningen, d.v.s. förekomsten

    av arter i vikarna var korrelerad till specifika år. Fiskyngelsammansättningen varierade

    även mycket med vikarnas öppenhet mot havet.

    Vi föreslår att inventeringsuppföljningar för naturtillståndsbedömning av grunda vikar

    görs med olika tidsintervaller för vegetation och fiskyngel samt för öppna och inneslutna vikar.

    Uppföljning av fiskyngelsamhället bör göras kontinuerligt och med korta tidsintervall,

    förslagsvis varje år, eftersom det är så stora mellanårsvariationer. Uppföljning av vegetationssamhället

    kan göras med längre tidsintervall i öppna vikar än i inneslutna vikar. Exempelvis

    kan vegetationen i öppna vikar inventeras enstaka år med påföljande tre till maximalt sex års

    intervall. För inneslutna vikar bör inventeringar ske vid tre på varandra följande år och därefter

    med exempelvis tre års intervall.

    Summary in English.

    The present study investigated inter-annual variations in the aquatic vegetation and young-ofthe-

    year (Y-O-Y) fish communities in shallow bays of the Baltic Sea. The aim of the study

    was to provide a scientific background and suggestions for monitoring time intervals for these

    coastal environments. Additionally, variations in the aquatic vegetation and Y-O-Y fish

    communities were studied in relation to the geographic location and morphometry of the bays.

    The surveys of vegetation and Y-O-Y fish were conducted in late July to September in 8

    counties along the Swedish Baltic Sea coast. In total 50 bays were analysed with respect to

    vegetation and 41 bays with respect to Y-O-Y fish.

    We found large variations between years in the mean percentage cover of large

    macrophytes and the cover of filamentous algae. The species composition was rather

    consistent in the bays between years. Only a few bays showed a large variation in species

    composition between years. These were mainly bays which were enclosed and very isolated

    from the sea. We did not find any synchronized variations in the species composition between

    years, i.e. the cover of certain species was not similarly high or low in several bays the same

    years. The variation in species composition could to a large extent be explained by latitude

    and the degree of isolation of bays from the sea.

    The Y-O-Y fish community varied considerably between years. The fish community

    showed a synchronized variation between years, i.e. the density of Y-O-Y fish species were

    correlated with specific years. Furthermore, the Y-O-Y fish community varied with the degree

    of isolation of bays from the sea.

    We suggest that monitoring of shallow coastal bays in the Baltic Sea should be

    conducted with different time intervals for the vegetation and Y-O-Y fish communities. We

    also suggest different time intervals for monitoring of open and enclosed isolated bays.

    Monitoring of the Y-O-Y fish community should be conducted with regular and short time

    intervals; every year would be advantageous. Monitoring of the submerged vegetation

    community could be conducted with long time intervals in open bays, e.g. 3 to maximum 6

    years. Enclosed isolated bays should be monitored at least 3 years in a row to get reliable

    results, but periods of yearly monitoring could be alternated with e.g. 3 year intervals.

  • 268.
    Hansen, Joakim P.
    Stockholm University, Faculty of Science, Department of Botany.
    Benthic vegetation in shallow inlets of the Baltic Sea: Analysis of human influences and proposal of a method for assessment of ecological status2012Report (Refereed)
    Abstract [en]

    The European Union Water Framework Directive (WFD) has a general objective that all European waters should attain good ecological status by 2015. Shallow wave-protected inlets with soft-sediment bottoms are common environments along the Swedish and Finnish Baltic Sea coastlines. However, there is no suitable method for assessing the ecological status of this biotope. The current assessment methods based on macrovegetation for coastal waters in Sweden and Finland are mainly designed for hard-bottom biotopes and function poorly for shallow soft bottoms. The aim of this study was to analyse the effects of human activities on submerged macrovegetation in shallow inlets along the Swedish and Finnish Baltic Sea coasts, and to develop a method for assessment of environmental status for the inlets.

    The results of the study showed that the proportion of disturbance-sensitive species decreased with increasing total phosphorus concentration and boating activity. In addition, macrophyte cover was lower in inlets with high, as compared to low, boating pressure. Natural environmental factors were found to be very important for explaining variation in the macrophyte community. However, a large part of the variation was unexplained in the models tested, and should be examined further.

    Based on the results, an assessment method for classification of environmental status was developed. The method uses a macrophyte index based on a cover proportion of sensitive to tolerant species, as well as the mean cover of all species combined. The two macrophyte responses are expressed as ecological quality ratios relative to a reference condition. Specific threshold values were developed to classify the environmental status on a five-point scale, from high to good, moderate, poor, and bad status. The method suggested can be used as a complement to the existing methods that are applied to deeper areas. The method is applicable to individual inlets and may also be suitable to larger water areas according to divisions in the WFD. It does, however, need further development and independent testing before application.

  • 269.
    Hansen, Joakim
    et al.
    Stockholm University, Faculty of Science, Department of Botany. Växtekologi.
    Robertson-Andersson, Deborah
    Troell, Max
    Department of Systems Ecology.
    Control of the herbivorous gastropod Fissurella mutabilis (Sow.) in a land-based integrated abalone-seaweed culture2006In: Aquaculture, Vol. 255, no 1-4, p. 384-388Article in journal (Refereed)
  • 270.
    Hansen, Joakim
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Sagerman, Josefin
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Sofia, Wikström
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Effects of plant morphology on small-scale distribution of invertebrates2010In: Marine Biology, ISSN 0025-3162, E-ISSN 1432-1793, Vol. 157, no 10, p. 2143-2155Article in journal (Refereed)
    Abstract [en]

    Habitat structure influences organism communities by mediating interactions between individuals and species, affecting abundance and species richness. We examined whether variations in the morphology of soft-bottom plants affect their function as habitat and whether complex structured plants support higher macroinvertebrate abundance and species richness. Three Baltic Sea plant species were studied, together with artificial plants resembling each species. In a field collection, we found higher invertebrate abundance on the morphologically more complex plants Myriophyllum spicatum and Chara baltica than on the structurally simpler plant Potamogeton perfoliatus. In a colonization experiment, we found the highest invertebrate abundance on artificial M. spicatum but found no difference between natural plants. Invertebrate taxon richness displayed no consistent relationship with plant structural complexity. The results imply that plant morphology influences small-scale invertebrate distribution, partly supporting the hypothesis that structurally complex plants harbour higher invertebrate abundance.

  • 271.
    Hansen, Joakim
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Wikström, Sofia
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Axemar, Hanna
    Stockholm University, Faculty of Science, Department of Botany.
    Kautsky, Lena
    Stockholm University, Faculty of Science, Department of Botany.
    Distribution differences and active habitat choices of invertebrates between macrophytes of different morphological complexity2011In: Aquatic Ecology, ISSN 1386-2588, E-ISSN 1573-5125, Vol. 45, no 1, p. 11-22Article in journal (Refereed)
    Abstract [en]

    This study explores: (1) whether the abundance of macroinvertebrates differs between macrophytes differing in both morphological complexity and tolerance to nutrient enrichment; (2) whether the distribution of invertebrates between macrophytes is due to active habitat choice; and (3) whether invertebrates prefer structurally complex to simple macrophytes. Macroinvertebrate abundance was compared between two common soft-bottom plants in the Baltic Sea that are tolerant to eutrophication, Myriophyllum spicatum and Potamogeton pectinatus, and one common plant that is sensitive to eutrophication, Chara baltica. Both field sampling and habitat choice experiments were conducted. We recorded higher total macroinvertebrate abundance on the structurally complex M. spicatum than on the more simply structured P. pectinatus and C. baltica, but found no difference in macroinvertebrate abundance between P. pectinatus and C. baltica. In accordance with the field results, our experiment indicated that the crustacean Gammarus oceanicus actively chose M. spicatum over the other macrophytes. Besides, we found that G. oceanicus actively preferred complex to simply structured artificial plants, indicating that the animal distribution was at least partly driven by differences in morphological complexity between plant species. In contrast, the gastropod Theodoxus fluviatilis did not make an active habitat choice between the plants. Our findings suggest that human-induced changes in vegetation composition can affect the faunal community. Increased abundance of structurally complex macrophytes, for example, M. spicatum, can result in increased abundance of macroinvertebrates, particularly mobile arthropods that may actively choose a more structurally complex macrophyte.

  • 272.
    Hansen, Joakim
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Wikström, Sofia
    Kautsky, Lena
    Stockholm University, Faculty of Science, Department of Botany.
    Effects of water exchange and vegetation on the macroinvertebrate fauna composition of shallow land-uplift bays in the Baltic Sea2008In: Estuarine, Coastal and Shelf Science, ISSN 0272-7714, E-ISSN 1096-0015, Vol. 77, no 3, p. 535-547Article in journal (Refereed)
    Abstract [en]

    Shallow bays with soft sediment bottoms are common habitats along the Swedish and Finnish Baltic Sea coastline. These bays undergo a process of geomorphometric evolution with the natural isostatic land-uplift process, whereby open bays and sounds decrease in depth and are gradually isolated from the sea, forming bays with narrow openings. This study tested the relationship between the morphometric isolation of the bays from the sea and the macroinvertebrate fauna community of these bays. Additionally, we tested the specific role of the submerged vegetation as an indicator of the macroinvertebrate fauna community. We chose two environmental factors for the analyses, water exchange of the bays and the taxon richness of the macroflora in the bays. We found a hierarchical relationship between water exchange, flora taxon richness, and fauna biomass and taxon richness using structural equation modelling: decreased biomass and taxon richness of fauna were related to decreased flora taxon richness, which in turn was related to decreased water exchange. Using multivariate redundancy analysis, the two environmental factors included in the model were found to explain 47.7% of the variation in the fauna taxon composition and 57.5% of the variation in the functional feeding groups of the fauna. Along the morphometric isolation gradient of the bays, the fauna assemblages changed from a community dominated by gastropods, bivalves, and crustaceans, to a community mainly consisting of a few insect taxa. Moreover, the proportion of predators, gathering collectors, and shredders increased while that of filtering collectors and scrapers decreased. Our results indicate that the density and taxon richness of macroinvertebrate fauna are higher in less morphometrically isolated bays than in more isolated bays in the Baltic Sea. Furthermore, we suggest that the taxon richness of macroflora can serve as an indicator of the fauna community.

  • 273.
    Hansen, Joakim
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Wikström, Sofia
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Kautsky, Lena
    Stockholm University, Faculty of Science, Department of Botany.
    Taxon composition and food-web structure in a morphometric gradient of Baltic Sea land-uplift bays2012In: Boreal environment research, ISSN 1239-6095, E-ISSN 1797-2469, Vol. 17, no 1, p. 1-20Article in journal (Refereed)
    Abstract [en]

    Shallow Baltic Sea bays undergo a process of morphometric isolation from the sea due to post-glacial land uplift. Recent studies have documented that both flora and fauna communities change along this gradient. Changes in taxon composition may in turn alter feeding ecology and trophic relationships. In addition, the relative importance of carbon from terrestrial sources may increase with bay isolation. In accordance with previous studies, we found a change in the community composition of both flora and fauna with bay isolation. Results of stable isotope analysis (δ13C, δ15N) suggested that epiphytes and periphyton are the major carbon sources for most benthic primary consumers, but that their importance in relation to angiosperms and charophytes decreased with bay isolation. The results also indicated that filter feeders utilize terrestrially derived carbon, but its importance could not be critically related to bay isolation. Trophic positions of the consumers were similar across the bay isolation gradient.

  • 274.
    Hansson, Christer
    et al.
    Dept Biol, Zool Museum, Lund, Sweden.
    Hambäck, Peter A.
    Stockholm University, Faculty of Science, Department of Botany.
    Three cryptic species in Asecodes (Forster) (Hymenoptera, Eulophidae) parasitizing larvae of Galerucella spp. (Coleoptera, Chrysomelidae), including a new species2013In: JOURNAL OF HYMENOPTERA RESEARCH, ISSN 1070-9428, Vol. 30, p. 51-64Article in journal (Refereed)
    Abstract [en]

    Three morphologically very similar species of Asecodes Forster (Hymenoptera: Eulophidae) are reviewed. Asecodes parviclava (Thomson) is removed from synonymy under A. lucens stat. rev., and differentiated from A. lucens (Nees) and A. lineophagum sp. n. All three species develop as gregarious endoparasitoids in larvae of Galerucella spp. (Coleoptera: Chrysomelidae), but each species has its own unique host range. Asecodes lineophagum attacks only Galerucella lineola (Fabr.) and A. lucens only G. sagittariae (Gyllenhal), whereas A. parviclava parasitizes G. tenella (L.), G. calmariensis (L.) and G. pusilla (Duftschmid). The Asecodes species are similar but display small though distinct morphological differences, and are distinguished also through molecular differences. The genetic distance in mitochondrial CO1 ranged from 2.3% to 7.3% between the species. Five names, one valid and four synonyms, were available for this group of species, but none of them was linked to a primary type. To promote stability of nomenclature, primary types are designated for all five names, neotypes for Eulophus lucens Nees, Entedon mento Walker and Derostenus parviclava Thomson, and lectotypes for Entedon chthonia Walker and Entedon metagenes Walker. Entedon mento, E. chthonia and E. metagenes remain synonymized under A. lucens.

  • 275. Herben, T
    et al.
    Münzbergová, Z
    Mildén, Mikael
    Stockholm University, Faculty of Science, Department of Botany.
    Ehrlén, Johan
    Cousins, Sara A O
    Eriksson, Ove
    Stockholm University, Faculty of Science, Department of Botany.
    Longterm spatial dynamics of Succisa pratensis in a changing rural landscape: linking dynamical modelling with historical maps2006In: Journal of Ecology, ISSN 0022-0477, E-ISSN 1365-2745, Vol. 94, no 1, p. 131-143Article in journal (Refereed)
    Abstract [en]

    We attempt to explain the current distribution of a long-lived perennial plant, Succisa pratensis, in a rural landscape in southern Sweden by linking its population biology with documented changes in the landscape, using a dynamical, spatially explicit model incorporating population dynamics and spatial spreading of the plant. Changes in the landscape were inferred from historical maps (1850 and 1900) and aerial photographs (1945 and 2001).

     

    We tested whether predictions for the current species distribution are affected by assumptions about its early 19th century distribution, to determine whether recent history and current processes are dominant, and how past landscape changes determine current distributions.

     

    Initial conditions influence predictions of current distribution, suggesting that the current distribution still partly reflects the distribution of the species in the early 19th century. A period of 150 years is too short for Succisa to have spread extensively if dispersal parameters are given realistic values.

     

    Simulations in which present-day land-use patterns were imposed at earlier dates showed that changes in landscape structure over the past 175 years also had a strong effect on the present-day habitat occupancy and population sizes of Succisa.

     

    The dominant process for Succisanow is extinction from marginal habitats. It is therefore likely that the (relatively) high present-day occupation patterns are still due to much larger areas having been available in the past rather than to successful dispersal. Although the species has responded to landscape changes, there is little evidence of population sizes reaching equilibrium.

     

    Our approach shows that the wealth of landscape information available from historical maps can be linked with data on population biology by means of dynamical models that can make predictions about species dynamics.

  • 276.
    Holmén Bränn, Kristina
    Stockholm University, Faculty of Science, Department of Botany.
    Pollination processes - maternal and offspring performance2007Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Pollination is one of the most important factors determining the reproductive success of plants. This thesis examines processes associated to varying pollination, with focus on plant responses. The first aim was to examine the possibility and constraints for short-term evolution of flower size in Raphanus raphanistrum. The results showed that there exists a possibility for pollinator-mediated short-term evolution of flower size in the study species. Flower size was strongly correlated to plant size. Since flower size cannot evolve separately from plant size, this correlation may constitute a constraint to the evolution of flower size. The second aim was to determine how varying pollen load affects later flowering, reproduction and growth of maternal plants. High pollen load treatment resulted in larger or more flowers on late flowers, which may enhance pollen dispersal and reproductive success, while the total seed mass was the same between treatments. The results indicate that the study species R. raphanistrum, Sinapis arvensis and Brassica napus have plastic responses in floral traits according to the present pollination level. The third aim was to determine how varying pollen load affects seed quality and offspring vigor. The results suggest that high pollen load had no positive effects on seed quality or offspring vigor due to pollen competition. Instead, seed mass determined seed quality and offspring vigor in the three study species and low pollen load treatment resulted in highquality offspring due to heavier seeds. The fourth aim was to examine causes and consequences of variation in reproductive success of Succisa pratensis on a regional scale. The results suggest that the most important variables, on a regional scale, for reproductive success were population size and habitat quality. The results showed that seed weight variation might be important when assessing reproductive success. In this study, seed weight variation did not seem to be adaptive.

  • 277.
    Holmén Bränn, Kristina
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Lehtilä, K.
    Maternal plant responses to high pollen loads2007In: International journal of plant sciences, ISSN 1058-5893, E-ISSN 1537-5315, Vol. 168, no 7, p. 1013-1019Article in journal (Refereed)
    Abstract [en]

    Maternal plant responses to different levels of pollination vary and are of importance for the total fitness of the plant. We studied how varying pollen load affects late flowering, reproduction, and growth of maternal plants. Raphanus raphanistrum, Sinapis arvensis, and Brassica napus were used as study species. We conducted hand‐pollination experiments with different pollen loads for early flowers in the inflorescence and measured responses on vegetative traits, floral traits of late flowers, and seed production. There were no effects on vegetative traits, but floral traits were affected by treatments in two of the study species. The high pollen load treatment in S. arvensis resulted in longer petals on late flowers compared with the low pollen load treatment. In R. raphanistrum, the high pollen load treatment resulted in a higher number of flowers, with narrower petals, than the low pollen load treatment. Total seed production was similar in both treatments in all species. Our results suggest that plants that received a high pollen load were able to allocate resources to high seed production of early flowers and to increased pollen dispersal of late flowers, thereby achieving higher total fitness than plants that received a lower pollen load.

  • 278.
    Holmén Bränn, Kristina
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Lehtilä, K.
    The effect of pollen load on seed quality and offspring vigor: the role of resource allocationManuscript (Other academic)
  • 279.
    Holmén Bränn, Kristina
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Mildén, M.
    Variation in reproductive success on a regional scale in Succisa pratensisManuscript (Other academic)
  • 280.
    Homma, T
    et al.
    Japan.
    Mizuta, Y
    Japan.
    Jige, M
    Japan.
    Yokota, K
    Japan.
    Nagafuchi, O
    Japan.
    Matsuo, K
    Japan.
    Greger, M
    Stockholm University, Faculty of Science, Department of Botany. Växtfysiologi.
    Luxova, Miroslav
    Academie of Science, Bratislava.
    Lux, Alexander
    Comenius University, Bratislava.
    Effects of cadmium treatment on tea plants.2008In: Abstract. Japanese Sociey for Root Research.: Root Research 17 (2)., 2008Conference paper (Other academic)
  • 281.
    Honkakangas, Jessica
    Stockholm University, Faculty of Science, Department of Botany.
    Spring succession on shallow rocky shores in northern Baltic proper2007Book (Other academic)
  • 282. Horvitz, Carol C.
    et al.
    Ehrlén, Johan
    Stockholm University, Faculty of Science, Department of Botany.
    Matlaga, David
    Context-dependent pollinator limitation in stochastic environments: can increased seed set overpower the cost of reproduction in an understorey herb?2010In: Journal of Ecology, ISSN 0022-0477, E-ISSN 1365-2745, Vol. 98, no 2, p. 268-278Article in journal (Refereed)
    Abstract [en]

    1. In the understorey herb Lathyrus vernus seed production is pollen limited, but increased reproduction results in a lower probability of remaining reproductive. Putting these two results together, previous research reported that population growth rate lambda was negatively impacted by high pollination. 2. Thus, costs and benefits have to be translated into the common currency of their respective effects on population dynamics to determine whether populations are truly pollen limited or whether they are already at an optimal level of pollination. 3. Also, when pollinators and demography vary from year to year we require a framework that examines reproductive benefits and demographic costs in the context of a variable environment. Whether or not additional pollination will increase the stochastic population growth rate lambda(S) depends upon the balance of stochastic elasticities of the costs and benefits. 4. In constant environment models, where seed survival, germination and seedling survival were increased, we found that the high cost of reproduction could be offset by improvements in seed survival and germination, but not by improvements of seedling survival. 5. In variable environment models, where changes in the sequence and frequencies of high- and low-pollination years mixed with occasional high-germination years were modelled, we found that increasing the frequency of high-germination conditions could offset the cost of reproduction, and the offset was even greater if high-germination years occurred after a high-pollination year or if high pollination was accompanied by high-germination conditions in the same year. 6. Both deterministic lambda and stochastic lambda(S) were less sensitive to perturbation of reproduction than to perturbation of the probability for flowering plants to remain reproductive. In other words, a small change in the parameter which is related to the 'cost' of reproduction had a bigger effect than a small change in the parameter which is related to the 'benefit' of increased pollination for Lathyrus. 7.Synthesis. Stochastic environment-specific elasticities for reproduction and stasis of flowering plants differ in their response to environmental context. The cost-benefit relationships, the ultimate fitness consequences of supplemental pollen, are influenced by the frequency and sequence of years differing in pollen availability and recruitment conditions.

  • 283. Huang, Wei-Ping
    et al.
    Sun, Hang
    Deng, Tao
    Razafimandimbison, Sylvain G.
    Stockholm University, Faculty of Science, Department of Botany.
    Nie, Ze-Long
    Wen, Jun
    Molecular phylogenetics and biogeography of the eastern Asian-eastern North American disjunct Mitchella and its close relative Damnacanthus (Rubiaceae, Mitchelleae)2013In: Botanical journal of the Linnean Society, ISSN 0024-4074, E-ISSN 1095-8339, Vol. 171, no 2, p. 395-412Article, review/survey (Refereed)
    Abstract [en]

    Mitchella is a small genus of the Rubiaceae with only two species. It is the only herbaceous semishrub of the family showing a disjunct distribution in eastern Asia and eastern North America, extending to Central America. Its phylogeny and biogeographical diversification remain poorly understood. In this study, we conducted phylogenetic and biogeographical analyses for Mitchella and its close relative Damnacanthus based on sequences of the nuclear internal transcribed spacer (ITS) and four plastid markers (rbcL, atpB-rbcL, rps16 and trnL-F). Mitchella is monophyletic, consisting of an eastern Asian M. undulata clade and a New World M. repens clade. Our results also support Michella as the closest relative to the eastern Asian Damnacanthus. The divergence time between the two intercontinental disjunct Mitchella species was dated to 7.73 Mya, with a 95% highest posterior density (HPD) of 3.14-12.53 Mya, using the Bayesian relaxed clock estimation. Ancestral area reconstructions suggest that the genus originated in eastern Asia. The semishrub Mitchella appears to have arisen from its woody ancestor in eastern Asia and then migrated to North America via the Bering land bridge in the late Miocene.

  • 284.
    Hylander, K.
    Stockholm University, Faculty of Science, Department of Botany.
    Aspect modifies the magnitude of edge effects on bryophyte growth in boreal forests2005In: Journal of Applied Ecology, Vol. 42, p. 518-525Article in journal (Refereed)
  • 285.
    Hylander, K.
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Dynesius, M.
    Causes of the large variation in bryophyte species richness and composition among boreal streamside forests?2006In: Journal of Vegetation Science, Vol. 17, p. 333-346Article in journal (Refereed)
  • 286.
    Hylander, K.
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Dynesius, M.
    Jonsson, B.G.
    Nilsson, C.
    Substrate form determines the fate of bryophytes in riparian buffer strips2005In: Ecological Applications, Vol. 15, p. 674-688Article in journal (Refereed)
  • 287.
    Hylander, K.
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Hedderson, T.A.
    Does the width of isolated ravine forests influence moss and liverwort diversity and composition? – a study of temperate forests in South Africa2007In: Biodiversity & Conservation, Vol. 16, p. 1441-1458Article in journal (Refereed)
  • 288.
    Hylander, K.
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Jonsson, B.G.
    The conservation ecology of cryptogams2007In: Biological Conservation, Vol. 135, p. 311-314Article in journal (Refereed)
  • 289.
    Hylander, K.
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Nilsson, C.
    Jonsson, B.G.
    Göthner, T.
    Differences in habitat quality explain nestedness in a land snail meta-community2005In: Oikos, Vol. 108, p. 351-361Article in journal (Refereed)
  • 290.
    Hylander, Kristoffer
    Stockholm University, Faculty of Science, Department of Botany.
    No increase in colonization rate of boreal bryophytes close to propagule sources2009In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 90, p. 160-169Article in journal (Refereed)
  • 291.
    Hylander, Kristoffer
    Stockholm University, Faculty of Science, Department of Botany.
    Riparian zones increase regional species richness by harboring different, not more, species: comment.2006In: Ecology, ISSN 0012-9658, Vol. 87, no 8, p. 2126-2128Article in journal (Refereed)
  • 292.
    Hylander, Kristoffer
    Stockholm University, Faculty of Science, Department of Botany.
    The response of land snail assemblages below aspens to forest fire and clear-cutting in Fennoscandian boreal forests2011In: Forest Ecology and Management, ISSN 0378-1127, E-ISSN 1872-7042, Vol. 261, no 11, p. 1811-1819Article in journal (Refereed)
    Abstract [en]

    Species can persist in a landscape with recurrent disturbances either through local survival or by dispersing to sites of a preferred successional stage. This study investigated in what extent forest floor dwelling land snails survived forest fires and clear-cutting. Snail fauna in LFH (litter, fermenting litter and humus) samples below retained aspen trees in disturbed areas were compared with samples under scattered aspens in adjacent forests by extracting snails from LFH samples below five aspens in several stands of each type (five forest fires, six clear-cuts, and seven undisturbed forests). LFH samples from burnt sites had a higher pH than from forests, but on average a lower abundance of individual snails (11 vs. 30 in 0.5 I LFH) and 50% lower species density (3 vs. 6 species). The abundances and species densities in the clear-cuts were less affected. There was generally a positive relationship between pH and both species density and abundance in all the stand types. Burning apparently depleted the snail fauna considerably and some species may be dependent on dispersal if they are to recover within the burnt area, while the snail assemblages at clear-cuts did not differ significantly in species composition from adjacent forests. The positive relationship between pH and snail prevalence on the burnt sites raises questions regarding the pre- and post-fire spatial variation in pH (and available minerals) within and among stands and how it relates to snail survival rates and their capacity to track suitable places after the disturbance. Retained aspens at clear-cuts seem to harbour a forest like land snail fauna.

  • 293.
    Hylander, Kristoffer
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Johnson, Samuel
    Stockholm University, Faculty of Science, Department of Botany.
    In situ survival of forest bryophytes in small-scale refugia after an intense forest fire2010In: Journal of Vegetation Science, ISSN 1100-9233, E-ISSN 1654-1103, Vol. 21, no 6, p. 1099-1109Article in journal (Refereed)
    Abstract [en]

    Question Species can persist in landscapes with recurring disturbances either by migrating to places suitable for the moment or by enduring the threatening conditions. We investigated to what extent boreal forest bryophytes survived an intense forest fire in situ and whether bryophytes had started to recolonize the area 7-8 years later. Location Tyresta National Park, eastern Sweden. Methods We recorded bryophytes in 14 burnt and 12 forest reference plots (50 x 50 m). In each plot we investigated 15 random 1-m2 micro-plots. In plots in the burnt area we also examined micro-plots at locations of all fire refugia, and in case of the forest references, of 10 potential refugia. Results We found on average three small refugia per 50 x 50-m plot; each containing on average 4.8 forest bryophytes, a level similar to that of micro-plots in the references, but significantly higher than in random micro-plots in the burnt plots (1.5 species). Many refugia were located in rocky areas, but few were in wet sites. The burnt area remained dominated by a few fire-favoured species, even if recolonization of forest bryophytes had begun. There was, however, no significant correlation between number of refugia and number of forest species in random micro-plots, leaving open the question of the importance of refugia as regulators of early succession. Conclusion We conclude that small-scale refugia can also occur for sensitive species such as forest bryophytes, and that the refugia in our case were frequently found on rocky or mesic rather than wet sites. The role of such refugia in recolonization, however, warrants further investigation.

  • 294.
    Hylander, Kristoffer
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Nemomissa, Sileshi
    Addis Ababa University.
    Complementary roles of home gardens and exotic tree plantations as alternative habitats for Ethiopian montane rainforest plant biodiversity2009In: Conservation Biology, ISSN 0888-8892, E-ISSN 1523-1739, Vol. 23, p. 400-409Article in journal (Refereed)
  • 295.
    Hylander, Kristoffer
    et al.
    Stockholm University, Faculty of Science, Department of Botany. Stockholm University, Faculty of Science, Department of Botany. Växtekologi.
    Nemomissa, Sileshi
    Home garden coffee as a repository of epiphyte biodiversity in Ethiopia2008In: Frontiers of Ecology and the Environment, Vol. 6, no 10, p. 524-528Article in journal (Refereed)
  • 296.
    Hylander, Kristoffer
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Pocs, Tamas
    Nemomissa, Sileshi
    Liverworts of southwest Ethiopian montane forests: ecological and biogeographical notes2010In: Journal of Bryology, ISSN 0373-6687, E-ISSN 1743-2820, Vol. 32, p. 92-100Article in journal (Refereed)
    Abstract [en]

    Ethiopia has diverse topographic features and climatic conditions with a diverse flora. The liverwort flora of southwest Ethiopia is practically unknown, despite a favourable climate and the occurrence of suitable ecosystems such as montane rainforests. During an ecological study of diversity patterns of bryophytes and vascular plants in relation to land use, we recorded many bryophyte species. In this paper we report the finding of 89 species of liverworts, and give short ecological notes and describe the distribution (locally and in Africa) for each species. Of these, 51 species are newly reported from Ethiopia. It is thus obvious that Ethiopia is considerably richer in liverworts than might be expected from previous checklists.

  • 297.
    Hylander, Kristoffer
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Weibull, Henrik
    Do time-lagged extinctions and colonizations change the interpretation of buffer strip effectiveness?: a study of riparian bryophytes in the first decade after logging2012In: Journal of Applied Ecology, ISSN 0021-8901, E-ISSN 1365-2664, Vol. 49, no 6, p. 1316-1324Article in journal (Refereed)
    Abstract [en]

    There is a risk that short-term studies either underestimate disturbance effects because of time-lagged responses, including both time-lagged extinctions and colonizations, or overestimate them because of fast recovery. To evaluate the conservation effectiveness of tree group retention (in this case, buffer strips along streams), we studied the bryophyte community once prior to, and twice after logging, comparing one buffer and one clear-cut plot (0.1 ha) in each of 13 riparian sites. We asked whether time-lagged responses or recovery processes had dominated the period between two re-inventories, 2.5 and 10.5 years after logging, focusing both on the whole community and on species of conservation concern. Although there were examples of recovering species in both clear-cuts and buffer strips, the similarity in species composition to predisturbance conditions had decreased in the second re-inventory. Even if the buffer strips displayed more time-lagged colonizations and local extinctions over the later period compared to the clear-cuts, the overall species composition in the buffer strips was still significantly more similar to the prelogging conditions than the clear-cuts. The red-listed species had mostly declined during the first period, and the number of red-list species per plot (mostly species growing on dead wood) was rather stable at <20% of predisturbance levels in clear-cuts and <60% in buffer strips in the last re-inventory. Synthesis and applications. We show that most extinctions of red-list species occurred soon after disturbance and that the conclusions drawn from a study carried out 2.5 years after the disturbance did not change profoundly 8 years later. Although the species composition in the buffer strips continued to change over time, sensitive species survived much better in buffer strips than in clear-cuts, which supports the practice of retaining buffer strips for terrestrial species too. This knowledge should encourage managers to find ways of increasing the efficacy of this practice. One obvious measure could be to retain wider strips or implement other management practices that make the buffer strips less sensitive to wind, which will lead to higher tree retention to support a prelogging species composition.

  • 298. Ickert-Bond, Stefanie M.
    et al.
    Rydin, Catarina
    Stockholm University, Faculty of Science, Department of Botany.
    MICROMORPHOLOGY OF THE SEED ENVELOPE OF EPHEDRA L. (GNETALES) AND ITS RELEVANCE FOR THE TIMING OF EVOLUTIONARY EVENTS2011In: International journal of plant sciences, ISSN 1058-5893, E-ISSN 1537-5315, Vol. 172, no 1, p. 36-48Article in journal (Refereed)
    Abstract [en]

    Micromorphology of the seed envelope of Ephedra (Gnetales) is known to be variable, but variation patterns have never been systematically documented. We test the usefulness of this feature for species determination and subclade delimitation in Ephedra and investigate the relationship of this character to infrageneric evolutionary patterns. Most species have a basically smooth seed envelope, which in some species appears slightly striate or reticulate due to convex or depressed outer periclinal cell walls. Ephedra rhytidosperma from China and Ephedra torreyana from North America have transverse lamellae formed by the epidermis. A papillate surface is found in respective close relatives of these two species. Micromorphology of the seed envelope is generally not useful for species identification or subclade delineation. The amount of variation is low, and intraspecific variation, which in some cases seems to be correlated with hybridization and/or introgression, complicates species recognition. Furthermore, parallel evolution of similar micromorphological patterns in unrelated subclades of Ephedra is evident and cannot be explained by similar seed dispersal mechanisms. The Asian species with transverse lamellae or papillae on the seed are dispersed by frugivores whereas similar American species are anemochoric. Transverse ridges occur in several Early Cretaceous fossil seeds with affinity to Ephedra. However, our results indicate that the resemblance between these fossils and extant taxa with similar features is superficial and convergent. In line with other recent studies, we find that Cretaceous ephedroids are extinct stem relatives to the extant clade.

  • 299.
    Idestam-Almquist, Jerker
    Stockholm University, Faculty of Science, Department of Botany.
    Temporal and spatial variation of submersed aquatic plants in the Baltic Sea1998Doctoral thesis, comprehensive summary (Other academic)
  • 300. Ilina, Elena L.
    et al.
    Logachov, Anton A.
    Laplaze, Laurent
    Demchenko, Nikolay P.
    Pawlowski, Katharina
    Stockholm University, Faculty of Science, Department of Botany.
    Demchenko, Kirill N.
    Composite Cucurbita pepo plants with transgenic roots as a tool to study root development2012In: Annals of Botany, ISSN 0305-7364, E-ISSN 1095-8290, Vol. 110, no 2, p. 479-489Article in journal (Refereed)
    Abstract [en]

    In most plant species, initiation of lateral root primordia occurs above the elongation zone. However, in cucurbits and some other species, lateral root primordia initiation and development takes place in the apical meristem of the parental root. Composite transgenic plants obtained by Agrobacterium rhizogenes-mediated transformation are known as a suitable model to study root development. The aim of the present study was to establish this transformation technique for squash. The auxin-responsive promoter DR5 was cloned into the binary vectors pKGW-RR-MGW and pMDC162-GFP. Incorporation of 5-ethynyl-2-deoxyuridine (EdU) was used to evaluate the presence of DNA-synthesizing cells in the hypocotyl of squash seedlings to find out whether they were suitable for infection. Two A. rhizogenes strains, R1000 and MSU440, were used. Roots containing the respective constructs were selected based on DsRED1 or green fluorescent protein (GFP) fluorescence, and DR5::Egfp-gusA or DR5::gusA insertion, respectively, was verified by PCR. Distribution of the response to auxin was visualized by GFP fluorescence or -glucuronidase (GUS) activity staining and confirmed by immunolocalization of GFP and GUS proteins, respectively. Based on the distribution of EdU-labelled cells, it was determined that 6-day-old squash seedlings were suited for inoculation by A. rhizogenes since their root pericycle and the adjacent layers contain enough proliferating cells. Agrobacterium rhizogenes R1000 proved to be the most virulent strain on squash seedlings. Squash roots containing the respective constructs did not exhibit the hairy root phenotype and were morphologically and structurally similar to wild-type roots. The auxin response pattern in the root apex of squash resembled that in arabidopsis roots. Composite squash plants obtained by A. rhizogenes-mediated transformation are a good tool for the investigation of root apical meristem development and root branching.

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