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  • 1.
    Algesten, Grete
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Ekologi och geovetenskap.
    Regulation of carbon dioxide emission from Swedish boreal lakes and the Gulf of Bothnia2005Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The global carbon cycle is subject to intense research, where sources and sinks for greenhouse gases, carbon dioxide in particular, are estimated for various systems and biomes. Lakes have previously been neglected in carbon balance estimations, but have recently been recognized to be significant net sources of CO2.

    This thesis estimates emission of carbon dioxide (CO2) from boreal lakes and factors regulating the CO2 saturation from field measurements of CO2 concentration along with a number of chemical, biological and physical parameters. Concentration of dissolved organic carbon (DOC) was found to be the most important factor for CO2 saturation in lake water, whereas climatic parameters such as precipitation, temperature and global radiation were less influential. All lakes were supersaturated with and, thus, sources of CO2. Sediment incubation experiments indicated that in-lake mineralization processes during summer stratification mainly occurred in the pelagial. Approximately 10% of the CO2 emitted from the lake surface was produced in epilimnetic sediments.

    The mineralization of DOC and emission of CO2 from freshwaters was calculated on a catchment basis for almost 80,000 lakes and 21 major catchments in Sweden, together with rates of sedimentation in lakes and export of organic carbon to the sea. The total export of terrestrial organic carbon to freshwaters could thereby be estimated and consequently also the importance of lakes for the withdrawal of organic carbon export from terrestrial sources to the sea. Lakes removed 30-80% of imported terrestrial organic carbon, and mineralization and CO2 emission were much more important than sedimentation of carbon. The carbon loss was closely related to water retention time, where catchments with short residence times (<1 year) had low carbon retentions, whereas in catchments with long residence times (>3 years) a majority of the imported TOC was removed in the lake systems.

    The Gulf of Bothnia was also studied in this thesis and found to be a net heterotrophic system, emitting large amounts of CO2 to the atmosphere on an annual basis. The rate of CO2 emission was depending on the balance between primary production and bacterial respiration, and the system was oscillating between being a source and a sink of CO2.

  • 2.
    Algesten, Grete
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Ekologi och geovetenskap.
    Sobek, Sebastian
    Bergström, Ann-Kristin
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Jonsson, Anders
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Tranvik, Lars J
    Jansson, Mats
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Contribution of sediment respiration to summer CO2 emission from boreal and subarctic lakes2005Inngår i: Microbial Ecology, ISSN 0095-3628, E-ISSN 1432-184X, Vol. 50, nr 4, 529-535 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We measured sediment production of carbon dioxide (CO(2)) and methane (CH(4)) and the net flux of CO(2) across the surfaces of 15 boreal and subarctic lakes of different humic contents. Sediment respiration measurements were made in situ under ambient light conditions. The flux of CO(2) between sediment and water varied between an uptake of 53 and an efflux of 182 mg C m(-2) day(-1) from the sediments. The mean respiration rate for sediments in contact with the upper mixed layer (SedR) was positively correlated to dissolved organic carbon (DOC) concentration in the water (r(2) = 0.61). The net flux of CO(2) across the lake surface [net ecosystem exchange (NEE)] was also closely correlated to DOC concentration in the upper mixed layer (r(2) = 0.73). The respiration in the water column was generally 10-fold higher per unit lake area compared to sediment respiration. Lakes with DOC concentrations <5.6 mg L(-1) had net consumption of CO(2) in the sediments, which we ascribe to benthic primary production. Only lakes with very low DOC concentrations were net autotrophic (<2.6 mg L(-1)) due to the dominance of dissolved allochthonous organic carbon in the water as an energy source for aquatic organisms. In addition to previous findings of allochthonous organic matter as an important driver of heterotrophic metabolism in the water column of lakes, this study suggests that sediment metabolism is also highly dependent on allochthonous carbon sources.

  • 3.
    Algesten, Grete
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Ekologi och geovetenskap.
    Sobek, Sebastian
    Bergström, Ann-Kristin
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Ågren, Anneli
    Tranvik, Lars J
    Jansson, Mats
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Role of lakes for organic carbon cycling in the boreal zone2004Inngår i: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 10, nr 1, 141-147 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We calculated the carbon loss (mineralization plus sedimentation) and net CO2 escape to the atmosphere for 79 536 lakes and total running water in 21 major Scandinavian catchments (size range 437–48 263 km2). Between 30% and 80% of the total organic carbon that entered the freshwater ecosystems was lost in lakes. Mineralization in lakes and subsequent CO2 emission to the atmosphere was by far the most important carbon loss process. The withdrawal capacity of lakes on the catchment scale was closely correlated to the mean residence time of surface water in the catchment, and to some extent to the annual mean temperature represented by latitude. This result implies that variation of the hydrology can be a more important determinant of CO2 emission from lakes than temperature fluctuations. Mineralization of terrestrially derived organic carbon in lakes is an important regulator of organic carbon export to the sea and may affect the net exchange of CO2 between the atmosphere and the boreal landscape.

  • 4. Arnqvist, Göran
    et al.
    Nilsson, Tina
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi och geovetenskap.
    The evolution of polyandry: multiple mating and female fitness in insects2000Inngår i: Animal Behaviour, Vol. 60, nr 2, 145-164 s.Artikkel i tidsskrift (Fagfellevurdert)
  • 5. Arnqvist, Göran
    et al.
    Nilsson, Tina
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi och geovetenskap.
    Katvala, Mari
    Mating rate and fitness in female bean weevils2005Inngår i: Behavioral Ecology, ISSN 1045-2249, Vol. 16, nr 1, 123-127 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Females of most animal taxa mate with several males during their lifespan. Yet our understanding of the ultimate causes of polyandry is incomplete. For example, it is not clear if and in what sense female mating rates are optimal. Most female insects are thought to maximize their fitness by mating at an intermediate rate, but it has been suggested that two alternative fitness peaks may be observed if multiple costs and benefits interact in determining the relationship between mating rate and fitness. We studied the relationship between female fitness and mating rate in the bean weevil, Callosobruchus maculatus (Coleoptera: Bruchidae), a species in which several distinct direct effects of mating to females have been reported. Our results show that female fitness, measured as lifetime offspring production, is lowest at an intermediate mating rate. We suggest that this pattern is the result of multiple direct benefits to mating (e.g., sperm replenishment and hydration/nutrition effects) in combination with significant direct costs to mating (e.g., injury from male genitalia). Females mating at low rates may efficiently minimize the costs of mating, whereas females mating at high rates instead may maximize the benefits of mating. If common, the existence of bimodal relationships between female mating rate and fitness may help explain the large intra- and interspecific variation in the degree of polyandry often seen in insects.

  • 6.
    Aunapuu, Maano
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi och geovetenskap.
    Predators in low arctic tundra and their impact on community structure and dynamics2004Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The abundance of predators and their impact on ecosystem dynamics is a vividly discussed topic in current ecology. In my studies, incorporating field observations, field experiments and theoretical modeling, I explored the importance of predators and predation in a low arctic tundra ecosystem in northern Norway. This involved observing the abundance and spatial activity of predators (raptors and small mustelids); manipulating the abundance of predators (spiders and birds) in an arthropod community; and exploring the theoretical consequences of intraguild predation on the coexistence among predators.

    The results show that predation is important both in the arthropod assemblage and, depending on the productivity of the community, in the vertebrate assemblage. In arthropod communities predators are at least as abundant as their prey, whereas in the vertebrate part of ecosystem, predators are substantially less abundant than their prey. Still, in both cases predators had strong impact on their prey, influencing the abundance of prey and the species composition of prey assemblages. The impact of predation cascaded to the plant community both in the reticulate and complex arthropod food web and in the linear food chain-like vertebrate community. In the vertebrate-based community we could even observe the long time scale effect on plant community composition.

    Within the predator community, exploitation competition and intraguild predation were the structuring forces. As the arthropod communities consist of predators with different sizes, intraguild predation is an energetically important interaction for top predators. As a consequence, they reduce the abundance of intermediate predators and the impact of intermediate predators on other prey groups. Moreover, being supported by intermediate predators, top predators can have stronger impact themselves on other prey groups.

    In vertebrate communities, intraguild predation seems to be unimportant as energetic link, instead it manifests as an extreme version of interference competition. Therefore intraguild predation reduces the likelihood of coexistence, as it is due limited prey diversity and intense exploitative competition already precarious in the low arctic tundra.

    In conclusion, predators have strong impact on their prey, especially in the more productive parts of the low arctic tundra. This applies even to the food webs with complex and reticulate structure, and these effects carry through the community both in the short time scale of population growth and on the long time scale of population generations.

  • 7.
    Aunapuu, Maano
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi och geovetenskap.
    Oksanen, Lauri
    Oksanen, Tarja
    Intraguild predation and coexistence in vertebrate predatorsManuskript (Annet vitenskapelig)
  • 8.
    Aunapuu, Maano
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi och geovetenskap.
    Oksanen, Tarja
    Habitat selection of coexisting competitors: a study of small mustelids in northern Norway2003Inngår i: Evolutionary Ecology, ISSN 0269-7653, Vol. 17, nr 4, 371-392 s.Artikkel i tidsskrift (Fagfellevurdert)
  • 9.
    Aunapuu, Maano
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi och geovetenskap.
    Oksanen, Tarja
    Atlegrim, Ola
    Predation structures the low arctic tundra arthropod communityManuskript (Annet vitenskapelig)
  • 10.
    Aunapuu, Maano
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi och geovetenskap.
    Oksanen, Tarja
    Oksanen, Lauri
    Grellmann, Doris
    Schneider, Michael
    Rammul, Üllar
    Biomass patterns in European tundra as a test of hypotheses on trophic dynamicsManuskript (Annet vitenskapelig)
  • 11.
    Berglund, H.
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi och geovetenskap.
    Jonsson, B. G.
    Predictability of plant and fungal species richness of old-growth boreal forest islands2001Inngår i: Journal of Vegetation Science, Vol. 12, 857-866 s.Artikkel i tidsskrift (Fagfellevurdert)
  • 12.
    Berglund, H.
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Ekologi och geovetenskap.
    Jonsson, B. G.
    Verifying an Extinction Debt among Lichens and Fungi in Northern Swedish Boreal Forests2005Inngår i: Conservation Biology, ISSN 0888-8892, E-ISSN 1523-1739, Vol. 19, nr 2, 338-348 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Destruction and fragmentation of natural habitats results in small species populations that face increased risk of extinction. A time delay may be involved in the regional extinction of species, and the number of species that eventually may go extinct in the future is called the “extinction debt.” In boreal Sweden, we examined whether the number of epiphytic crustose lichens and wood-inhabiting fungi in old-growth forest remnants diverges from species richness levels in forest patches that have been naturally isolated for millennia. An excess of species in forest remnants could indicate the presence of an extinction debt. Observed species richness in 32 old-growth forest remnants (also called woodland key habitats [WKHs]) was compared with predicted species richness. To predict species richness we used regression models based on data from 46 isolated old-growth forest patches in a forest-wetland matrix. The reference landscape is ancient and assumed to reflect the conditions of insular floras in dynamic equilibrium. Stand factors constituted predictive variables in the models. The observed number of lichen species was higher than expected (i.e., an extinction debt among lichens may exist). By contrast, there was no significant difference between observed and expected species richness among wood-inhabiting fungi. The species richness of wood-inhabiting fungi has adjusted to the changes in forest and landscape structure more rapidly than the species richness of lichens. Differences in substrate dynamics between epiphytes on living trees and species growing on decaying logs might explain the difference between species groups. The results also indicate that population densities of red-listed species were low, which may result in continuing extinctions of red-listed species. The importance of WKHs might be overvalued because species may be lost if conservation efforts consider only protection and preservation of WKHs.

  • 13.
    Berglund, Håkan
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi och geovetenskap.
    Biodiversity in fragmented boreal forests: assessing the past, the present and the future2004Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The aims of this thesis are to (1) analyze the predictability (indicators) of plant and fungal species diversity in old-growth forests, and (2) assess the history and biodiversity of woodland key habitats (WKHs) and their potential to maintain species diversity in fragmented boreal forest landscapes.

    Predictability was explored in Granlandet nature reserve, an unexploited landscape composed of discrete old-growth Picea forest patches of varying size isolated by wetland, reflecting conditions of insular biota at stochastic equilibrium. Data from 46 patches (0.2-12 ha) showed that most species were rare. However, species richness and composition patterns exhibited a high degree of predictability, which strengthen the possibility to apply biodiversity indicators in old-growth forest stands. Area was a key factor. The increase in species richness starts to level out at 2-3 ha. Large patches host more Red-list species in their interiors than do small ones, i.e. stand size is an important qualitative aspect of old-growth habitat. Nestedness emerged in relation to area but also in equal-sized plots. Structural complexity and habitat quality were important for species richness and compositional patterns, and small habitats of high quality could harbor many rare species. Monitoring of wood-fungi on downed logs showed that species diversity on downed logs changed over periods of 5-10 years and that the occurrences of annual species were unpredictable. It is suggested that monitoring of species with durable fruit bodies (mainly polypores) is likely to be a feasible approach to obtain comparable data over time.

    Assessments of biodiversity of WKHs were performed in two areas with contrasting histories of forest exploitation, namely in south boreal and north boreal Sweden. Analyses of the history of 15 south boreal WKHs showed that fire-suppression, selective logging until mid-20th century and abandonment by modern forestry has shaped their forest structure. These WKHs are not untouched forests, they lack key structural components and harbor few Red-list species. Artificial interventions to restore natural processes and patterns are needed to further increase their suitability for threatned species. Modeling analyses of species richness in 32 WKHs in north boreal Sweden, some of which have not been isolated by modern forestry until recently, indicated an excess of crustose lichen species, i.e. WKHs may face delayed species extinctions. By contrast, the results indicate that wood-fungi have tracked the environmental changes. Differences in substrate dynamics between epiphytes on living trees and species growing on decaying logs may explain the diffeence between species groups. The results indicate that population densities of Red-list species were low, which may result in further depletion of species diversity.

    Continuing species declines and extinctions are likely if not conservation of WKHs are combined with other considerations in th managed forest landscape. Both WKHs and their surroundings must be managed and designed to maintain biodiversity over time. For a successful future conservation of boreal forest biodiversity monitoring of WKHs must be combined with monitoring of refeence areas.

  • 14.
    Berglund, Håkan
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Ekologi och geovetenskap.
    Edman, Mattias
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Ekologi och geovetenskap.
    Ericson, Lars
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Ekologi och geovetenskap.
    Temporal variation of wood-fungi diversity in boreal old-growth forests: implications for monitoring2005Inngår i: Ecological Applications, ISSN 1051-0761, E-ISSN 1939-5582, Vol. 15, nr 3, 970-982 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Monitoring programs that supply reliable and sufficient information on numbers and types of organisms are essential for following changes in biodiversity. In boreal Fennoscandia, forest-dwelling species are threatened in managed forest landscapes and, thus, are of particular concern for conservation strategies. Wood fungi represent key ecological components in the boreal forest that are sensitive to forestry and widely used as indicators in large-scale forest inventories for identifying valuable forest habitats. Knowledge of their natural dynamics is required for designing monitoring programs to assess the adequacy of conservation strategies. We studied the occurrence of corticoids (Corticiaceae) and polypores (Polyporaceae) over time at different spatial scales in unexploited boreal old-growth forests. Data from 70 downed logs followed during an eight-year period showed that the lifespan of fruit bodies of most species was shorter than four years. Even perennial species followed this pattern, although fruit bodies of some species (e.g., Phellinus spp.) remained vital throughout the eight years studied. Both species richness and species composition on individual logs changed markedly over the eight years due to deterministic succession of species paralleling the wood decay. By contrast, data from the stand scale, i.e., seven 0.1 -ha plots, showed that species richness and species composition of polypores did not undergo any major changes during a six-year period. A majority of all recorded polypore species (80%) were already present at the first inventory. However, although species richness remained constant at the stand scale, corticoid species composition differed between years, reflecting their short-lived, annual fruit bodies. This study suggests that monitoring should be performed at stand scale and focus on species with durable fruit bodies, e.g., polypores. This will provide data that can be used both to detect future changes in biodiversity in old-growth spruce forests and to evaluate conservation strategies.

  • 15.
    Bergsten, Johannes
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Ekologi och geovetenskap.
    A review of long-branch attraction2005Inngår i: Cladistics, ISSN 1096-0031, Vol. 21, nr 2, 163-193 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The history of long-branch attraction, and in particular methods suggested to detect and avoid the artifact to date, is reviewed. Methods suggested to avoid LBA-artifacts include excluding long-branch taxa, excluding faster evolving third codon positions, using inference methods less sensitive to LBA such as likelihood, the Aguinaldo et al. approach, sampling more taxa to break up long branches and sampling more characters especially of another kind, and the pros and cons of these are discussed. Methods suggested to detect LBA are numerous and include methodological disconcordance, RASA, separate partition analyses, parametric simulation, random outgroup sequences, long-branch extraction, split decomposition and spectral analysis. Less than 10 years ago it was doubted if LBA occurred in real datasets. Today, examples are numerous in the literature and it is argued that the development of methods to deal with the problem is warranted. A 16 kbp dataset of placental mammals and a morphological and molecular combined dataset of gall waSPS are used to illustrate the particularly common problem of LBA of problematic ingroup taxa to outgroups. The preferred methods of separate partition analysis, methodological disconcordance, and long branch extraction are used to demonstrate detection methods. It is argued that since outgroup taxa almost always represent long branches and are as such a hazard towards misplacing long branched ingroup taxa, phylogenetic analyses should always be run with and without the outgroups included. This will detect whether only the outgroup roots the ingroup or if it simultaneously alters the ingroup topology, in which case previous studies have shown that the latter is most often the worse. Apart from that LBA to outgroups is the major and most common problem; scanning the literature also detected the ill advised comfort of high support values from thousands of characters, but very few taxa, in the age of genomics. Taxon sampling is crucial for an accurate phylogenetic estimate and trust cannot be put on whole mitochondrial or chloroplast genome studies with only a few taxa, despite their high support values. The placental mammal example demonstrates that parsimony analysis will be prone to LBA by the attraction of the tenrec to the distant marsupial outgroups. In addition, the murid rodents, creating the classic “the guinea-pig is not a rodent” hypothesis in 1996, are also shown to be attracted to the outgroup by nuclear genes, although including the morphological evidence for rodents and Glires overcomes the artifact. The gall wasp example illustrates that Bayesian analyses with a partition-specific GTR + Γ + I model give a conflicting resolution of clades, with a posterior probability of 1.0 when comparing ingroup alone versus outgroup rooted topologies, and this is due to long-branch attraction to the outgroup.

     

  • 16.
    Bergsten, Johannes
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi och geovetenskap.
    Taxonomy, phylogeny, and secondary sexual character evolution of diving beetles, focusing on the genus Acilius2005Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Sexual conflict can lead to antagonistic coevolution between the sexes, but empirical examples are few. In this thesis secondary sexual characters in diving beetles are interpreted in the light of sexual conflict theory. Whether the male tarsal suction cups and female dorsal modifications are involved in a coevolutionary arms race is tested in two ways. First eight populations of a species with dimorphic females that varied in frequency of the morphs were investigated and male tarsal characteristics quantified. The frequency of female morphs is shown to be significantly correlated to the average number and size of male tarsal suction cups in the population, a prediction of the arms race hypothesis. Second, the hypothesis is tested in a phylogenetic perspective by optimizing the secondary sexual characters on a phylogeny. A full taxonomic revision of the genus Acilius is presented, including new synonyms, lectotype designations, geographic distributions based on more than five thousand examined museum specimens and the description of a new species from northeastern USA. Specimens of all species (except one possibly extinct that failed to be found in Yunnan, China 2000), were field collected between 2000 and 2003 in Sardinia, Sweden, Russia, Honshu and Hokkaido in Japan, New York, Maryland, California and Alberta. Three genes (CO1, H3 and Wingless) were sequenced from the fresh material as well as scoring a morphological character matrix all of which was used to derive a robust and complete hypothesis of the phylogenetic relationship in the group. The phylogeny was derived using Bayesian phylogenetics with Markov Chain Monte Carlo techniques and received a posterior probability of 0.85. Changes in male and female characters turned out to be perfectly correlated across the phylogeny, providing one of the best empirical examples to date of an antagonistic arms race between the sexes in a group of organisms. Finally, a review of a pitfall to phylogenetic analysis known under the name long-branch attraction (LBA), is provided. The problem is well known theoretically but has been questioned to occur in real data, and LBA has been in the core center of the hard debate between parsimony and likelihood advocates since different inference methods vary in sensitivity to the phenomenon. Most important conclusions from the review are; LBA is very common in real data, and is most often introduced with the inclusion of outgroups that almost always provide long branches, pulling down long terminal ingroup branches towards the root. Therefore it is recommended to always run analyses with and without outgroups. Taxon sampling is very important to avoid the pitfall as well as including different kind of data, especially morphological data, i.e. many LBA-affected conclusions have recently been reached by analyses of few taxa with complete genomes. Long-branch extraction (incl. outgroup exclusion), methodological disconcordance (parsimony vs modelbased), separate partition analyses (morphology vs molecules, codon positions, genes, etc), parametric simulation (incl. random outgroups), and split graphs are available relevant methods for the detection of LBA that should be used in combinations, because none alone is enough to stipulate LBA.

  • 17.
    Bergsten, Johannes
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi och geovetenskap.
    Miller, Kelly B.
    Female diving beetles in antagonistic coevolutionary arms race with male suckersManuskript (Annet vitenskapelig)
  • 18.
    Bergsten, Johannes
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi och geovetenskap.
    Töyrä, Anne
    Nilsson, Anders N.
    Intraspecific variation and intersexual correlation in secondary sexual characters of three diving-beetles (Coleoptera: Dytiscidae)2001Inngår i: Biological Journal of the Linnean Society, Vol. 73, nr 2, 221-232 s.Artikkel i tidsskrift (Fagfellevurdert)
  • 19.
    Bergström, Lena
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi och geovetenskap.
    Macroalgae in the Baltic Sea: responses to low salinity and nutrient enrichment in Ceramium and Fucus2005Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The brackish Baltic Sea is a marginal environment for both marine and freshwater species. The rate of ecological differentiation is presumably high due to strong selection pressure from a gradient of decreasing salinity that has been present in its current state for only about 3 000 years. Even more recently, increased nutrient loading due to human activities has affected the growth rate of species, with potential effects on their competitive interactions and responses to other regulating factors. I have investigated the potential effects of low salinity and nutrient enrichment on the distributional ranges of two marine macroalgae with a wide distribution in the Baltic Sea, the red alga Ceramium tenuicorne (Kütz.) Wærn and the brown alga Fucus vesiculosus L.

    A field study in the northern Baltic Sea indicated a strong relationship between the community structure of macroalgae and abiotic factors even on a small, local scale. The abiotic factors are potentially modulated by eutrophication, which may have a strong effect on the depth distribution and abundance of macroalgae. On a regional scale, laboratory experiments suggested that nutrient enrichment is unlikely to affect the distribution of Ceramium and Fucus along the salinity gradient. Growth in Ceramium from the Baltic Proper was enhanced by nitrate and phosphate, but the response did not override growth constraints due to low salinity. Ceramium from the Gulf of Bothnia had an inherently lower growth rate that was not positively affected by nitrate and phosphate increase. In Fucus vesiculosus, reproductive performance was impaired by nitrate and phosphate levels corresponding to ambient levels in eutrophicated areas of the Baltic Sea, when measured by their effect on zygote attachment, germination, and rhizoid development.

    The wide distribution of Ceramium in the inner Baltic Sea is probably related to local adaptation, rather than a generalized tolerance of different salinity levels. Ecotypic differences were observed when comparing strains from the Baltic Proper (salinity 7 psu) and the Gulf of Bothnia (4 psu). A high rate of vegetative reproduction was evident, although sexual reproduction was occasionally observed in salinity 4. In Fucus vesiculosus, genetic and morphological analyses of sympatric and allopatric populations of the common, vesicular, morphotype and a dwarf morphotype, characteristic for the Gulf of Bothnia, showed that the dwarf morphotype represents a separate evolutionary lineage. Also, vegetative reproduction was observed in Fucus for the first time, as supported by genetic and experimental data.

    The results show that the biota of the inner Baltic Sea may have unique adaptive and genetic properties, and that it is highly relevant to consider subspecies diversity in Baltic Sea management.

  • 20.
    Bergström, Lena
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi och geovetenskap.
    Berger, Rita
    Kautsky, Lena
    Negative direct effects of nutrient enrichment on the establishment of Fucus vesiculosus in the Baltic Sea2003Inngår i: European Journal of Phycology, Vol. 38, 41-46 s.Artikkel i tidsskrift (Fagfellevurdert)
  • 21.
    Bergström, Lena
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi och geovetenskap.
    Eklund, Britta
    Bruno, Ellen
    Kautsky, Lena
    Reproductive strategies of Ceramium tenuicorne near its inner limit in the brackish Baltic Sea2003Inngår i: Botanica Marina, Vol. 46, 125-131 s.Artikkel i tidsskrift (Fagfellevurdert)
  • 22.
    Bergström, Lena
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi och geovetenskap.
    Kautsky, Lena
    Local adaptation in Ceramium tenuicorne (Ceramiales, Rhodophyta) within the Baltic Sea salinity gradientManuskript (Annet vitenskapelig)
  • 23.
    Bergström, Lena
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Ekologi och geovetenskap.
    Tatarenkov, Andrei
    Jönsson, Rita B
    Johannesson, Kerstin
    Kautsky, Lena
    Morphological and genetic differentiation of Fucus vesiculosus in the brackish Baltic SeaInngår i: Journal of Phycology, ISSN 0022-3646, E-ISSN 1529-8817Artikkel i tidsskrift (Fagfellevurdert)
  • 24.
    Bergström, Ulf
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi och geovetenskap.
    Spatial heterogeneity and biotic interactions: scaling from experiments to natural systems2004Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Much of current ecological theory stems from experimental studies. These studies have often been conducted in closed systems, at spatial scales that are much smaller than the systems of interest. It is known that the outcome of these experiments may be seriously affected by artefacts associated with the caging procedures, as well as by the actual difference in spatial scale between experimental and target system. Yet, quantitative methods for estimating and removing artefacts of enclosure and for extrapolating experimental results to the scales of natural systems are largely lacking.

    The aim of this thesis was to confront some of the problems encountered when scaling from experiments to nature in studies on predator-prey systems, with focus on effects of changes in spatial heterogeneity. Specifically, I examined mechanisms that may cause consumption rate estimates to depend on the size of the experimental arena. I also studied methods for scaling up these process rate estimates to natural predator-prey systems. The studies were performed on invertebrate predator-prey systems found in the northern Baltic Sea. Initially, a descriptive study of small-scale distribution patterns was performed, in order to get background information on how the behaviour of the organisms was manifested in the spatial structure of the community. Experimental studies of two predator-prey systems exposed an artefact that may be widespread in experiments aiming at quantifying biotic interactions. It is caused by predator and prey aggregating along the walls of the experimental containers. This behaviour affects the encounter rate between predator and prey, thereby causing consumption rates to be scale-dependent. Opposing the common belief that larger arenas always produce less biased results, this scale effect may instead be reduced by decreasing arena size. An alternative method for estimating the magnitude of, and subsequently removing, the artefact caused by aggregation along the arena wall was presented.

    Once unbiased estimates of process functions have been derived, the next step is to scale up the functions to natural systems. This extrapolation entails a considerable increase in spatial heterogeneity, which may have important implications for the dynamics of the system. Moment approximation provides a method of taking the heterogeneity of natural populations into account in the extrapolation process. In the last study of the thesis, the concepts of moment approximation and how to estimate relevant heterogeneity were explained, and it was shown how the method may be used for adding space as a component to a dynamic predator-prey model. It was concluded that moment approximation provides a simple and useful technique for dealing with effects of spatial variation, and that a major benefit of the method is that it provides a way of visualising how heterogeneity affects ecological processes.

  • 25.
    Bergström, Ulf
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi och geovetenskap.
    Englund, Göran
    Estimating predation rates in experimental systems: scale-dependent effects of aggregative behaviour2002Inngår i: Oikos, Vol. 97, 251-259 s.Artikkel i tidsskrift (Fagfellevurdert)
  • 26.
    Bergström, Ulf
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Ekologi och geovetenskap.
    Englund, Göran
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Spatial scale, heterogeneity and functional responses2004Inngår i: Journal of Animal Ecology, ISSN 0021-8790, E-ISSN 1365-2656, Vol. 73, nr 3, 487-493 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    1. In a laboratory experiment, we studied the effect of arena size on the functional response of the mysid shrimp Neomysis integer preying on the cladoceran Polyphemus pediculus. The aim of the study was to examine mechanisms that cause the functional response to be scale-dependent, by documenting the spatial distribution and the movement behaviour of predator and prey.

    2. The attack rate was significantly higher in large arenas, while the handling time did not differ between arena sizes. The difference in attack rate could be explained by differences in aggregative behaviour of predator and prey and in swimming activity of the predator. It is suggested that distributions of animals are often affected by the walls of the experimental arenas and that this spatial heterogeneity is scale-dependent, which may have a considerable impact on estimates of ecological process rates.

    3. A method of correcting attack rate estimates for artefacts caused by such spatial heterogeneity is presented.

  • 27.
    Bergström, Ulf
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi och geovetenskap.
    Englund, Göran
    Bonsdorff, Erik
    Small-scale spatial structure of Baltic Sea zoobenthos - inferring processes from patterns2002Inngår i: Journal of Experimental Marine Biology and Ecology, Vol. 281, 123-136 s.Artikkel i tidsskrift (Fagfellevurdert)
  • 28.
    Bergström, Ulf
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi och geovetenskap.
    Englund, Göran
    Leonardsson, Kjell
    Plugging space into predator-prey models: an empirical approachManuskript (Annet vitenskapelig)
  • 29.
    Bigler, Christian
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi och geovetenskap.
    Diatoms as indicators of Holocene climate and environmental change in northern Sweden2001Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The objective of the thesis was to explore the potential of diatoms (Bacillariophyceae) as indicators of Holocene climate and environmental change in northern Sweden (Abisko region, 68°21'N, 18°49'E). A modern surface-sediment calibration set including 100 lakes was developed and lake-water pH, sedimentary organic content (assessed by loss-on-ignition) and temperature were identified as most powerful environmental variables explaining the variance within the diatom assemblages. Transfer functions based on unimodal species response models (WA-PLS) were developed for lake-water pH and mean July air temperature (July T), yielding coefficients of determination of 0.77 and 0.70, and prediction errors based on leave-one-out cross-validation of 0.19 pH units and 0.96 °C for lake-water pH and July T, respectively. The transfer functions were validated with monitoring data covering two open-water seasons (lake-water pH) and meteorological records covering the 20th century (July T). The good agreement between diatom-based inferences and measured monitoring data confirmed the prediction ability of the developed transfer functions.

    Analysing a Holocene sediment core from a lake nearby Abisko (Vuoskkujávri), diatoms infer a linearly decreasing July T trend (1.5 °C) since 6,000 cal. BP, which compares well with inferences based on chironomids and pollen from the same sediment core. The lake-water pH inference shows a pattern of moderate natural acidification (c. 0.5 pH units) since the early Holocene, reaching present-day pH values at c. 5,000 cal. BP. By fitting fossil diatom samples to the modern calibration set by means of residual distance assessment within canonical correspondence analysis (CCA), the early Holocene (between 10,600 and 6,000 cal. BP) was identified as a problematic time-period for diatom-based inferences and, consequently, reconstructions during this period are tentative. Pollen-based inferences also show 'poor' fit between 10,600 and 7,500 cal. BP and chironomids probably provide the most reliable July T reconstruction at Vuoskkujávri, with 'poor' fit only during the initial part of the Holocene (between 10,600 and 10,250 cal. BP).

    Possible factors confounding diatom-based July T inferences were investigated. Using detrended CCA (DCCA), Holocene sediment sequences from five lakes indicate that during the early Holocene, mainly physical factors such as high minerogenic erosion rates, high temperature and low light availability may have regulated diatom assemblages, favouring Fragilaria species. In all five lakes, diatom assemblages developed in a directional manner, but timing and scale of development differed substantially between lakes. The differences are attributed primarily to the geological properties of the lake catchments (with strong effects on lake-water pH), but other factors such as climatic change, vegetation, hydrologic setting and in-lake processes appear to regulate diatom communities in each lake differently. The influence of long-term natural acidification on diatom assemblages progressively declined during the Holocene with corresponding increase of the influence of climatic factors.

  • 30.
    Bigler, Christian
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Ekologi och geovetenskap.
    Grahn, E.
    Larocque, I.
    Jeziorski, A.
    Hall, Roland
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Ekologi och geovetenskap.
    Holocene environmental change at Lake Njulla (999 m asl), northern Sweden: a comparison with four small nearby lakes along an altitudinal gradient2003Inngår i: Journal of Paleolimnology, ISSN 0921-2728, E-ISSN 1573-0417, Vol. 29, nr 1, 13-29 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We assess Holocene environmental change at alpine Lake Njulla (68degrees22'N, 18degrees42'E, 999 m a.s.l.) in northernmost Sweden using sedimentary remains of chironomid head capsules and diatoms. We apply regional calibration sets to quantitatively reconstruct mean July air temperature (using chironomids and diatoms) and lake-water pH (using diatoms). Both chironomids and diatoms infer highest temperatures (1.7-2.3degreesC above present-day estimates, including, a correction for glacio-isostatic land up-lift by 0.6degreesC) during the early Holocene (c. 9,500-8,500 cal. yrs BP). Diatoms suggest a decreasing lake-water pH trend (c. 0.6 pH units) since the early Holocene. Using detrended canonical correspondence analysis (DCCA), we compare the Holocene development of diatom communities in Lake Njulla with four other nearby lakes (Lake 850, Lake Tibetanus, Vuoskkujavri, Vuolep Njakajaure) located along an altitudinal gradient. All five lakes show similar initial DCCA scores after deglaciation, suggesting that similar environmental processes such as high erosion rates and low light availability associated with high summer temperature appear to have regulated the diatom community, favouring high abundances of Fragilaria species. Subsequently, the diatom assemblages develop in a directional manner, but timing and scale of development differ substantially between lakes. This is attributed primarily to differences in the local geology, which is controlling the lake-water pH. Imposed on the basic geological setting, site-specific processes such as vegetation development, climate, hydrological setting and in-lake processes appear to control lake development in northern Sweden.

  • 31.
    Bigler, Christian
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Ekologi och geovetenskap.
    Hall, Roland I
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Ekologi och geovetenskap.
    Diatoms as indicators of climatic and limnological change in Swedish Lapland: A 100-lake calibration set and its validation for paleoecological reconstructions2002Inngår i: Journal of Paleolimnology, ISSN 0921-2728, E-ISSN 1573-0417, Vol. 27, nr 1, 97-115 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This study investigated the distribution of subfossil diatom assemblages in surficial sediments of 100 lakes along steep ecological and climatic gradients in northernmost Sweden (Abisko region, 67.07degrees N to 68.48degrees N latitude, 17.67degrees E to 23.52degrees E longitude) to develop and cross-validate transfer functions for paleoenvironmental reconstruction. Of 19 environmental variables determined for each site, 15 were included in the statistical analysis. Lake-water pH (8.0%), sedimentary loss-on-ignition (LOI, 5.9%) and estimated mean July air temperature (July T, 4.8%) explained the greatest amounts of variation in the distribution of diatom taxa among the 100 lakes. Temperature and pH optima and tolerances were calculated for abundant taxa. Transfer functions, based on WA-PLS (weighted averaging partial least squares), were developed for pH (r(2) = 0.77, root-mean-square-error of prediction (RMSEP) = 0.19 pH units, maximum bias = 0.31, as assessed by leave-one-out cross-validation) based on 99 lakes and for July T (r(2) = 0.75, RMSEP = 0.96 degreesC, max. bias = 1.37 degreesC) based on the full 100 lake set. We subsequently assessed the ability of the diatom transfer functions to estimate lake-water pH and July T using a form of independent cross-validation. To do this, the 100-lake set was divided in two subsets. An 85-lake training-set (based on single limnological measurements) was used to develop transfer functions with similar performance as those based on the full 100 lakes, and a 15-lake test-set (with 2 years of monthly limnological measurements throughout the ice-free seasons) was used to test the transfer functions developed from the 85-lake training-set. Results from the intra-set cross-validation exercise demonstrated that lake-specific prediction errors (RMSEP) for the 15-lake test-set corresponded closely with the median measured values (pH) and the estimations based on spatial interpolations of data from weather stations (July T). The prediction errors associated with diatom inferences were usually within the range of seasonal and interannual variability. Overall, our results confirm that diatoms can provide reliable and robust estimates of lake-water pH and July T, that WA-PLS is a robust calibration method and that long-term environmental data are needed for further improvement of paleolimnological transfer functions.

  • 32.
    Bigler, Christian
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Ekologi och geovetenskap.
    Hall, Roland I
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Ekologi och geovetenskap.
    Diatoms as quantitative indicators of July temperature: a century-scale validation with meteorological data from northern Sweden2003Inngår i: Palaeogeography, Palaeoclimatology, Palaeoecology, ISSN 0031-0182, E-ISSN 1872-616X, Vol. 189, nr 3-4, 147-160 s.Artikkel i tidsskrift (Fagfellevurdert)
  • 33.
    Bigler, Christian
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Ekologi och geovetenskap.
    Larocque, Isabelle
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Ekologi och geovetenskap.
    Peglar, S. M.
    Birks, H. J. B.
    Hall, Roland I.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Ekologi och geovetenskap.
    Quantitative multiproxy assessment of long-term patterns of Holocene environmental change from a small lake near Abisko, northern Sweden2002Inngår i: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 12, nr 4, 481-496 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Quantitative reconstructions are made of Holocene changes in climatic and environmental conditions from analyses of pollen, chironomids and diatoms in identical stratigraphic levels of a sediment core from Vuoskku-javri (68degrees20'43 N, 19degrees06'00 E, 348 m a.s.l.) near Abisko in northern Sweden (Lapland). Transfer functions, based on regional calibration sets, are applied to reconstruct Holocene patterns in mean July air temperature (using all three indicators). mean January air temperature (pollen), annual precipitation (pollen) and lakewater pH (diatoms). During periods with 'good' fit to the modern calibration sets all mean July air-temperature inferences based on the three proxy indicators reveal a general trend of decreasing temperature: pollen-inferred mean July air temperature shows a decrease of c, 1.1degreesC since 7500 cal. yrs BP; the chironomids show a decrease of c. 1.2degreesC since the early Holocene whereas the diatoms show a decrease of c. 1.5degreesC since 6000 cal. yrs BP. Pollen-inferred mean January air temperature indicates that winters may have been warmer by c. 3.0degreesC during the early Holocene, followed by a gradual cooling until 8500 cal. yrs BP (c. 1.0degreesC warmer than today) and a subsequent warming until 7000 cal. yrs BP (c. 2.0degreesC warmer than today). Since 7000 cal, yrs BP, a gradual cooling towards the present-day values is inferred. According to the pollen, annual precipitation may have been considerably higher during the early Holocene than today (c. +150 mm) and increased until 7000 cal. yrs BP (c. +320 mm). Since 7000 cal. yrs BP, annual precipitation decreased continuously towards present-day values. Diatom-inferred pH trends show that natural acidification of c. 0.5 pH units followed deglaciation; present-day values were reached c. 5000 cal. yrs BP. The early Holocene is identified as a problematic time period for the application of modern calibration sets. as diatoms show 'poor' fit to the calibration set from 10 600 to 6000 cal. yrs BP. pollen from 10 600 to 7500 cal. yrs BP, and chironomids from 10 250 to 10 000 cal. yrs BP. Compared with estimates from the COHMAP GCM model, mean July air-temperature inferences based on biological proxies at Vuoskkujavri suggest a more moderate decrease in temperature over the past 9000 years.

  • 34. Bolnick, Daniel
    et al.
    Svanbäck, Richard
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Ekologi och geovetenskap.
    Fordyce, James
    Yang, Louie
    Davis, Jeremy
    Hulsey, Darrin
    Forister, Matthew
    The ecology of individuals: incidence and implications of individual specialization2003Inngår i: American Naturalist, Vol. 161, 1-28 s.Artikkel i tidsskrift (Fagfellevurdert)
  • 35.
    Bonander, Sofie
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi, miljö och geovetenskap.
    Lyhamn, Louise
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi och geovetenskap.
    Kommunernas hantering av kattrelaterade frågor gällande förvildade tamkatter, herrelösa katter samt lösspringande katter i tätbebyggt område2004Independent thesis Advanced level (degree of Master (One Year)), 20 poäng / 30 hpOppgave
  • 36.
    Brodin, Tomas
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi och geovetenskap.
    Johansson, Frank
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi och geovetenskap.
    Conflicting selection pressures on the growth/predation risk trade-off in a damselfly2004Inngår i: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 85, nr 11, 2927-2932 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Activity is an important behavioral trait that in most animals mediates a trade-off between obtaining food for growth and avoiding predation. Active individuals usually experience a higher encounter rate with food items and predators and, as a consequence, grow faster and suffer higher predation pressure than less active individuals. We investigated how predator-induced mortality and growth of the damselfly Coenagrion hastulatum depend on activity at the level of the genotype. Larvae from six different C. hastulatum families were reared in two different predator treatments: predator present or absent. Families differed in activity, and active families grew to a significantly larger size than less-active families. Within families there was a plastic response to predators. Larvae reared without predators were more active and grew larger than larvae reared with a nonlethal predator. In the presence of a lethal predator the active families experienced higher mortality than the less active families. The results illustrate that the growth/predation-risk trade-off was mediated by activity and clearly show a cost of antipredator behavior. They also suggest that variation in activity level might be genetically regulated and could explain why C. hastulatum are abundant in aquatic systems both with and without potential predators.

  • 37.
    Dahlman, L
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi och geovetenskap.
    Näsholm, T
    Palmqvist, K
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi, miljö och geovetenskap.
    Growth, nitrogen uptake, and resource allocation in the two tripartite lichens Nephroma arcticum and Peltigera aphthosa during nitrogen stress2002Inngår i: New Phytologist, ISSN 0028-646X, Vol. 153, nr 2, 307-315 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

     

    • The lichens were irrigated with different N forms, enriched in 15N to assess N uptake, during 3 months in the field, with a total N dosage of 500 mg m−2. Nitrogen deprivation was induced by removing the nitrogen-fixing cephalodia.

    • The lichens took up 11–134 mg N m−2 of the added N, corresponding to 1–4% of their total thallus N. Uptake was 4 times higher for NH4+ than for NO3, and the highest 15N concentrations were found in newly synthesized tissue. Both forms of N stress affected thallus expansion rates in both species.

    • It is concluded that the two lichens were able to maintain a balanced tissue N concentration despite large variations in N supply, and that assimilated N might be transported to growing apices. Alternatively, N assimilation from external sources might be greater in the margins than in the mature thallus. Thallus expansion was sensitive to N stress, apparently being tightly coupled to N assimilation.

  • 38.
    Dahlman, L
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi och geovetenskap.
    Persson, J
    Näsholm, T
    Palmqvist, K
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi, miljö och geovetenskap.
    Carbon and nitrogen distribution in the green algal lichens Hypogymnia physodes and and Platismatia glauca in relation to nutrient supply.2003Inngår i: Planta, ISSN 0032-0935, Vol. 217, nr 1, 41-48 s.Artikkel i tidsskrift (Fagfellevurdert)
  • 39.
    Dahlman, L
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi och geovetenskap.
    Persson, J
    Palmqvist, K
    Näsholm, T
    Organic and inorganic nitrogen uptake in lichens.Inngår i: Planta, ISSN 0032-0935Artikkel i tidsskrift (Fagfellevurdert)
  • 40.
    Dahlman, Lena
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi och geovetenskap.
    Resource aquisition and allocation in lichens2003Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Lichens are fascinating symbiotic systems, where a fungus and a unicellular alga, most often green (bipartite green algal lichens; 90% of all lichens), or a fi lamentous cyanobacterium (bipartite cyanobacterial lichens; 10% of all lichens) form a new entity (a thallus) appearing as a new and integrated organism: in about 500 lichens the fungus is associated with both a cyanobacterium and an alga (tripartite lichens). In the thallus, the lichen bionts function both as individual organisms, and as a symbiont partner. Hence, in lichens, the participating partners must both be able to receive and acquire resources from the other partner(s) in a controlled way.

    Lichens are particularly successful in harsh terrestrial environments. In part this is related to their poikilohydric nature and subsequent ability to repeatedly become desiccated and hydrated. Metabolic activity, i.e. photosynthesis, respiration, and for cyanobacterial lichens N2-fixation, is limited to periods when the thallus is suffi ciently hydrated. Mineral nutrients are mainly acquired from dry or wet deposition directly on the thallus. Taken together it then appears that lichens are to a large extent passively controlled by their environment, making their control over resource allocation and acquisition particularly challenging.

    The aim of this thesis was to investigate resource acquisition and allocation processes in different lichens, and to see how these respond to changes in resource availability. This was done by following lichen growth in the fi eld during manipulation of water, light, and nutrient supply, and by assessing the responses of both the integrated thallus as well as the individual bionts. As a fi rst step, resource allocation and acquisition was investigated for a broad range of lichens aiming to determine the magnitude of metabolic variation across lichens. Seventy-fi ve lichen species were selected to cover as broad a spectrum as possible regarding taxonomy, morphology, habitat, and nitrogen requirements. The lichens had invested their nitrogen resources so that photosynthetic capacity matched respiratory carbon demand around a similar equilibrium across the contrasting species. Regulation of lichen growth was investigated in another study, using the two tripartite species Nephroma arcticum and Peltigera aphthosa, emphasizing the contribution of both internal and external factors. The empirical growth models for the two lichens were similar, showing that weight gain is to a higher extent dependent on those external factors that regulate their photosynthesis, whilst area gain is more controlled by internal factors, such as their nitrogen metabolism. This might be inferred from another study of the same species, where nitrogen manipulations resulted in an undisturbed weight gain, a similar resource allocation pattern between the bionts, but a distorted area gain.

    Aiming to investigate lichen nitrogen relations even further, lichens’ capacities to assimilate combined nitrogen in the form of ammonium, nitrate and amino acids were assessed using 14 contrasting boreal species. All these had the capacity to assimilate all the three nitrogen forms, with ammonium absorption being more passive, and nitrate uptake being low in bipartite cyanobacterial lichens. Differences in uptake capacities between species were more correlated to photobiont than to morphology or substrate preferences. Finally, to investigate intra-specifi c plasticity in relation to altered nutrient supply, resource investments between photo- and mycobiont were investigated in the two bipartite green algal lichens Hypogymnia physodes and and Platismatia glauca in a low and a high nutrient environ- in a low and a high nutrient environ- ment. In both species, more of the resources had been directed to the photobiont in the high nutrient environment also increasing their overall carbon status. Taken together, my studies indicate that in spite of the apparent passive environmental control on lichen metabolism, these symbiotic organisms are able to both optimize and control their resource acquisition and allocation processes.

  • 41.
    Dahlman, Lena
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Ekologi och geovetenskap.
    Palmqvist, Kristin
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Ekologi och geovetenskap.
    Growth in two foliose tripartite lichens Nephroma arcticum and Peltigera aphthosa: empirical modelling of external versus internal factors2003Inngår i: Functional Ecology, ISSN 0269-8463, E-ISSN 1365-2435, Vol. 17, nr 6, 821-831 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    1 To assess how internal and external factors contribute to lichen growth, light, water and nutrient supplies were manipulated during 3 months in the field for the lichens Nephroma arcticum (L.) Torss. and Peltigera aphthosa (L.) Willd. Concomitant measures of weight and area gain, microclimatic conditions and investments in photobiont vs mycobiont tissue were also conducted.

    2 In both lichens ≈80% of the variation in weight gain was explained by a linear regression model including light received during wet active periods, chlorophyll a concentration and area gain. All three parameters had a positive effect on weight gain.

    3 About 80% of the variation in area gain was explained by a model including variation in weight gain, initial thallus specific weight, ergosterol and chitin concentration. The model was identical for the two lichens, with a positive effect of weight gain and thallus specific weight and a negative effect of ergosterol and chitin.

    4 Peltigera aphthosa grew faster than N. arcticum when exposed to the same environmental conditions. This could be explained by its higher chlorophyll a to ergosterol ratio, and a greater water-holding capacity prolonging the active time in light.

  • 42.
    Dahlström, N.
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi och geovetenskap.
    Nilsson, C.
    Influence of channel characteristics on the retention of coarse particulate organic material in boreal, headwater streamsArtikkel i tidsskrift (Fagfellevurdert)
  • 43.
    Dahlström, N.
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi och geovetenskap.
    Nilsson, C.
    The dynamics of coarse woody debris in boreal regions are similar between stream channels and adjacent riparian forestsManuskript (Annet vitenskapelig)
  • 44.
    Dahlström, Niklas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Ekologi och geovetenskap.
    Function and dynamics of woody debris in boreal forest streams2005Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The work in this thesis deals with (1) the effects of woody debris on stream channel morphology and retention of organic material, and (2) the dynamics of woody debris and its relation to riparian forest history and composition. The studied stream reaches are situated in mature, productive forests in the boreal zone of Sweden.

    Wood variables were important predictors of the frequency of debris dams, pool area, the proportion of pools formed by wood, and variation in the bankfull channel width. Pools formed by woody debris were mainly created by damming and had larger surface areas and residual depths than pools formed by other agents. Stream reaches intersecting old-growth forest (with minor influence of forest management) had coarser and longer woody debris pieces, greater amounts of wood, more debris dams, and wood-formed pools compared to streams surrounded by forests influenced by selective logging.

    The influence of past forest management on the quality and quantity of woody debris in streams were analyzed by using dendrochrnological methods. Selective loggings and absence of forest fires after 1831 resulted in lower input rates and a gradual replacement of pine by sruce over time. Residence times in stream channels of woody debris (>10 cm in basal diameter) were long and the oldest dated pieces of pine and spruce were over 300 and 100 years, respectively.

    Dynamics of woody debris were explored by comparing wood volumes and characteristics between stream channels and their riparianforests and between old growth and managed sites. Wood volumes recorded in the stream channels exceeded, but were related to, the volumes found in the riparian forests. Limited input of woody debris by bank cutting and absence of slope processes suggest that recruitment processes of woody debri to stream channels are similar as in riparian forests and slow decay in channels results in greater volumes.

    The retentiveness of organic material in stream channels was examined by using release and capture experiments in multiple reaces during varying discharges using different sizes of leaf mimics. Sixty eight percent of the variation in retention was explained by a multiple regression model including discharge and leaf mimic siz. Between 44 and 80% of the variation in retention among reaches was explained by channel constraint, gravel coverage, and woody debris variables as the most important. Estimates from a partial least squares (PLS) model suggest an increase in mean transport distances by 22 to 53% in managed forest streams compared to old growth conditions and in a low wood scenario, mean transport distances increased by 38 to 99% with larger increases for higher discharges and larger particle sizes.

    To regain more pristine conditions of stream channels, management and restoration are needed to increase the amount of woody debris that recreates lost channel structures and increaes the retention of organic material.

  • 45. Dangles, O
    et al.
    Jonsson, M
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi och geovetenskap.
    Malmqvist, B
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi och geovetenskap.
    The importance of detritivore species diversity for maintaining stream ecosystem functioning following the invasion of a riparian plant2002Inngår i: Biological Invasions, Vol. 4, 441-446 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The strength of linkages between riparian plants and stream communities can be expected to be influenced by invading plants. While most studies so far have been focussed on the effects of the leaf litter quality of the invader, this study addresses the impact of detritivores on the pool of detritus. In a natural setting, we found that species richness of shredding macroinvertebrates significantly influenced the breakdown rate of an invasive weed species, the Japanese knotweed (Fallopia japonica), which has become a major plant invader along streams and rivers in Europe and North America. Our findings imply that a reduction of the diversity of shredder species, which may be the result of disturbances, could negatively influence stream ecosystems'' capacity of processing knotweed leaves. Although the knotweed showed breakdown rates similar to those of common native tree and shrub species, other exotic leaf species might show considerably slower rates and hence have greater consequences for the ecosystems. We have, in this study, indicated a technique by which the effects of other non-indigenous plants on ecosystem functioning might be considered.

  • 46. Dynesius, Mats
    et al.
    Zinko, Ursula
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi och geovetenskap.
    Correlation in species numbers among vascular plants, mosses, liverworts and lichens in boreal forests: effects of plot size, substrate affiliation, and stand age.Manuskript (Annet vitenskapelig)
  • 47.
    Ekerholm, Per
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi och geovetenskap.
    Population dynamics of tundra-living grey-sided voles2003Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    This thesis deals with the dynamics of tundra living voles with emphasis on the most common one, the grey-sided vole (Clethrionomys rufocanus). The tundra area chosen for the study was Finnmarksvidda, a vast flatland in northernmost Norway. All small mammal herbivores in the area showed dramatic fluctuations, and field experiment were conducted in order to elucidate these density fluctuations. The specific subjects addressed included: 1/ Temporal and spatial appearance of density fluctuations of voles and lemmings in the area, 2/ The generality of the density patterns observed, 3/ The impact of predation by vole predators during summertime, 4/ The impact of grey-sided vole grazing on food plants of different preference in a predator free environment, in the presence and absence of extra food, and 5/ The impact of food availability on density and demography of grey-sided voles in a predator free environment.

    The results achieved showed that voles in the slope and lowland had cyclic density fluctuations with 5 years duration. The cycles consisted of four phases: an increase phase, a peak phase, a decline phase and a crash phase. In the unproductive lowland and on the moderately productive slope, small pockets of productive habitats seemed to work as “triggers” for the cycles. The lemming fluctuations in the upper plateau (separated from the slope by a steep zone of boulders) differed markedly from the vole patterns in the lowland.

    Only two lemming peaks were recorded in twenty years. Both peaks had very short increase phases, a knife-sharppeak phase and no decline phase before the crash. A comparison between our results and lemming and vole populations from two other areas in Fennoscandia revealed the same difference in fluctuation pattern between lemmings and voles as seen in our area. This results suggests that lemmings in barren tundra highlands and voles in slightly more productive tundra lowlands are regulated by different mechanisms.

    The exclusion of vole predators from vole populations during summertime led to increase in overall vole density. Densities of the clumsy field vole (Microtus agrestis) and juveniles of all species showed the strongest positive effects of the exclusion.

    An experiment analysing the effects of food availability was conducted in islands in a large lake where grey-sided voles were introduced to predator free islands . Supplemental food was given to the voles in two unproductive, and two productive islands. Two unproductive and two productive islands were used as reference islands. The density of voles and the vole weight were higher in both the islands with supplemental food and those with high natural productivity. Increased vole density did not significantly increase grazing damage to plants. The cyclic density pattern of the voles in the nearby mainland (that harboured resident vole specialist predators as stoat and weasel) showed little resemblance to the seasonal fluctuations found in the islands (devoid of resident vole specialist predators). This result suggested that predation by stoat and weasel on grey-sided vole populations may cause the cyclic vole fluctuations seen in the area.

  • 48.
    Ekerholm, Per
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi och geovetenskap.
    Hambäck, Peter
    Oksanen, Lauri
    Effects of spatial isolation, habitat quality, and supplemental food for population dynamics of the grey-sided vole, Clethrionomys rufocanusManuskript (Annet vitenskapelig)
  • 49.
    Ekerholm, Per
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi och geovetenskap.
    Oksanen, Lauri
    Oksanen, Tarja
    Long-term dynamics of voles and lemmings at the timberline and above the willow limit as a test of hypothesis on trophic interactions2001Inngår i: Ecography, ISSN 0906-7590, Vol. 24, 555-568 s.Artikkel i tidsskrift (Fagfellevurdert)
  • 50.
    Ekerholm, Per
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi och geovetenskap.
    Oksanen, Lauri
    Oksanen, Tarja
    Schneider, Michael
    The impact of short-term predator removal on vole dynamics in a subarctic-alpine habitat complexInngår i: Oikos, ISSN 0030-1299Artikkel i tidsskrift (Fagfellevurdert)
123 1 - 50 of 128
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