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  • 51.
    Eklöv, Peter
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Effects of behavioural flexibility and habitat complexity on predator-prey interactions in fish communities1995Doctoral thesis, comprehensive summary (Other academic)
  • 52. Eklöv, Peter
    et al.
    Svanbäck, Richard
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Predation favors adaptive morphological variation in perch populationsManuscript (Other academic)
  • 53. Ericsson, T. S.
    et al.
    Berglund, H.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Östlund, L.
    History and forest biodiversity of woodland key habitats in south boreal SwedenArticle in journal (Refereed)
  • 54.
    Eriksson, Britas Klemens
    et al.
    Department of Plant Ecology, Uppsala University, Uppsala, Sweden.
    Bergström, Lena
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Local distribution patterns of macroalgae in relation to environmental variables in the northern Baltic Proper2005In: Estuarine, Coastal and Shelf Science, ISSN 0272-7714, E-ISSN 1096-0015, Vol. 62, no 1-2, p. 109-117Article in journal (Refereed)
    Abstract [en]

    The relationship between macroalgal assemblages and abiotic factors was quantified by gradient analyses in an area where long-term changes in macroalgal depth distributions have previously been documented. Biomass data from 4, 6, 8 and 10 m depth in an area of similar salinity (5) and substrate (rock) in the northern Baltic Proper was constrained by a set of environmental variables defining different aspects of abiotic control of species distributions (sediment cover, effective fetch, clarity index, the curvature and slope of the bottom, and direction of exposure) in multivariate analyses at different scales. Fucus vesiculosus dominated the biomass at 4, 6 and 8 m depth, andFurcellaria lumbricalis at 10 m. The applied models explained 30.7–53.3% of the total variance in community structure, and 49.3–60.9% when analysed separately for each depth. A separate analysis of species depth distributions demonstrated that effective fetch was most strongly related to upper limits of the algal belts, sediment cover to the lower limit and density of the F. vesiculosusbelt, and clarity index to the lower limits of F. vesiculosus, perennial red algae, and of the red algal and Sphacelaria spp. belts. The results show a strong correlation between environmental variables and vegetation structure even on a small, local scale in the northern Baltic Proper, indicating a high suitability of the phytobenthic zone for environmental monitoring. The results add to previous studies that show a strong importance of abiotic factors on large-scale variation in phytobentic community composition in the Baltic Sea.

  • 55.
    Eriksson, Torleif
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Migratory behaviour of Baltic salmon (Salmo salar L.): adaptive significance of annual cycles1988Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis evaluates the adaptive significance of annual cycles on the migratory behaviour of Baltic salmon (Salmo salar L.). The studies have included field experiments as well as laboratory studies gf maturity and migratory behaviour patterns of smolts and postsmolts mainly from the Angerman river population.

    Contrasting to the phenotypical elasticity in life-history traits, Baltic salmon was found to have a rather strict temporal organization of their annual behavioural patterns. Two year old smolted Baltic salmon showed drastic differences in migratory behaviour when compared in tanks containing either fresh or brackish water. Freshwater kept fish showed an annual cycle where downstream displacement in the upper water column was followed by a stationary behaviour, indicating a readaption to a freshwater life. Fish in brackish water behaved as a migratory fish throughout tne study. Baltic salmon also showed differences in maturation patterns in fresh and brackish water. Three summer old males detained in freshwater all matured sexually the following autumn. If transferred to sea and kept in net- pens a low proportion matured, mainly previously matured males. Furthermore there was a size- dependent relationship of sexual rematuration. Many small previously matured males did not migrate, similarly small previolusly matured males were unable to respond to shifts in the environment. With larger size the alternatives of sexual maturation and high growth rate wi more related to the environmental conditions the fish experienced.

    A hypothesis has been tested assuming that Baltic salmon migration is influenced by an annual time program. According to the hypothesis the migratory distance covered in the Baltic should be a result of a migratory activity sequence rather than a definite goal orientation. Fish detained before release generally showed a shorter distance between release point and area of recapture compared to fish released at normal time of smoltrun. The migratory distance appeared to be inversly related to the period of delay before release. A seasonal difference in migratory propensity was recorded.

    An instantaneous mortality curve for Baltic salmon during seaward migration and early sea-phase was estimated based on recapture data on sequentially related fish. The weekly mortality rate decreased from an initial mean of 271 during onset of migration, to 3.51 in mean during autumn. The high risk of mortality during the first part of migration indicated that strong selective forces act on a precise seasonal timing of migration.

  • 56.
    Eriksson, Torleif
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Mortality risks of Baltic salmon (Salmo salar L.) during downstream migration and the early sea-phase [Elektronisk resurs]: effects of body-size and season1988Manuscript (preprint) (Other academic)
    Abstract [en]

    Mortality risks in Baltic salmon during early migration was estimated through a sequential release experiment. Effects of time of release and size of fish on survival rate were studied.

    A protected transfer to the sea and an acclimatization prior to release increased the recapture rates by 1.6 to 2.0 times compared to fish released in the river. Furthermore, fish with a delayed release had a 2.8 to 5.0 times higher recapture rate than smolts released in the river.

    I found a strong positive correlation between the size of the fish and recapture rates during all three experimental years. Mortality rates peaked during the downstream migration and entry in to the sea. The weekly risk of mortality during the two first weeks was estimated to be 27.8%. Thereafter the mortality risk declined rapidly to 6.1% per week during the following 8-9 weeks. From mid September until the end of November the estimated mortality rate was only 3.5% per week.

    Baltic salmon appears to migrate at a sub-optimal size with respect to survival during migration. A gain in survival by a larger size during migration,could be obtained by a prolonged freshwater residency. However this is considered to be outweighted by the option of an accelerated growth rate in the sea.

  • 57.
    Fick, Jerker
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Pommer, Linda
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Åstrand, Anders
    Östin, Ronny
    Nilsson, Calle
    Andersson, Barbro
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    The effect of mechanical ventilation systems on the chemistry in the supply airArticle in journal (Refereed)
  • 58. Finsinger, Walter
    et al.
    Bigler, Christian
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science. NCCR Climate, Institute of Plant Sciences, University of Bern, Altenbergrain 21, CH-3013, Bern, Switzerland.
    Kraehenbuehl, Urs
    Lotter, Andre F
    Ammann, Brigitta
    Human impacts and eutrophication patterns during the past similar to 200 years at Lago Grande di Avigliana (N. Italy)2006In: Journal of Paleolimnology, ISSN 0921-2728, E-ISSN 1573-0417, Vol. 36, no 1, p. 55-67Article in journal (Refereed)
    Abstract [en]

    A short sediment core from Lago Grande di Avigliana (Piedmont, Italy), the second most eutrophied lake in Italy, was analysed for pollen and diatoms to reconstruct land-use changes and to estimate baseline conditions for total phosphorus (TP) in the water column. Varve counts on sediment thin-sections and (210)Pb, (226)Ra, and (137)Cs dating provided a reliable chronology for the past similar to 200 years. The main pollen-inferred land-use changes showed a sharp decrease of hemp retting around AD 1900, as well as a gradual change to less intensive agriculture and increasing abundance of exotic plants since AD similar to 1970. Diatom-inferred TP reconstructions indicated stable TP concentrations until AD similar to 1950, revealing baseline mesotrophic conditions (TP < 25 mu g l(-1)). After AD similar to 1950, TP values increased distinctly and continuously, culminating in the late 1960s with concentrations of 150 mu g l(-1). Subsequently, diatoms implied a linear decrease of TP, with an inferred value of 40 mu g l(-1) in the surface sediment sample. Comparison with instrumental TP measurements from the water column since AD 1980 showed a rapid recovery and allowed a direct validation of the diatom TP inference. However, although the TP concentration has decreased considerably, baseline conditions have not yet been reached. When compared to the limnological effects of sewage discharges on inferred-TP concentration, our results indicated that agricultural land use played a minor role in the lake's eutrophication.

  • 59. Hambäck, Peter
    et al.
    Ekerholm, Per
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Mechanisms of apparent competition in seasonal environments: an example with vole herbivory1997In: Oikos, ISSN 0030-1299, Vol. 80, p. 276-288Article in journal (Refereed)
  • 60.
    Hoffsten, Per-Ola
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Rarity in boreal stream: patterns, causes and consequences2003Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Patterns of site occupancy among boreal stream insects were studied in central Sweden with focus on sparsely distributed species and the role of dispersal and niche limitations.

    In the study of dispersal limitation, I found that effects of an extraordinarily harsh winter in small to medium-sized streams were strongest in sites located in small streams and far from lake outlets. Species richness and the total abundance of macroinvertebrates and trout returned to pre-disturbance levels after three years. However, some species showed slow recolonization and the proportion of holoaquatic taxa was still reduced after three years. In a second study, I found a positive correlation between site occupancy in stream caddisflies and morphological traits associated with fast and energy-efficient flight, whereas specialized spring caddisflies showed a negative correlation to these traits compared to stream species. This suggested that streams, but not springs, select for strong dispersal ability in caddisflies. In a survey of springs in central Sweden, hydrogeology was found to be a useful predictor of the occurrence of spring specialists. Two of these, Crunoecia irrorata Curtis and Parachiona picicornis (Pictet), were found exclusively in glaciofluvial springs, characterized by a stable discharge and temperature. Less specialized members of the spring fauna (i.e. species also occurring in streams, ponds or lakes) also occurred in moraine and limestone springs characterized by more unstable conditions.

    Niche limitations were studied by contrasting large-scale distributions of closely related rare and common stoneflies. Differences in temperature requirements in the juvenile stages and life cycles suggested that the rare species, Isogenus nubecula Newman, was restricted by a limited tolerance to low stream temperatures, whereas the two common species, Isoperla grammatica (Poda) and Diura nanseni (Kempny), appeared to have a broader tolerance to climatic conditions in the study area. In a second study of niche limitations, macroinvertebrate assemblages in 88 streams in Central Sweden showed a nested distribution pattern. Most species deviating from expected distributions occurred in small streams, indicating competitive exclusion from species-rich sites, predator avoidance, or specialization to unique habitat features of small streams. In the last paper, the longitudinal distribution of filter-feeding caddisflies in a lake-outlet stream demonstrated patterns concordant to feeding specialization.

  • 61.
    Hoffsten, P.-O.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Distribution of filter-feeding caddisflies (Trichoptera) and plankton drift in a Swedish lake-outlet stream.1999In: Aquatic Ecology, ISSN 1386-2588, Vol. 33, no 4, p. 377-386Article in journal (Refereed)
  • 62.
    Hoffsten, P.-O.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Effects of an extraordinarily harsh winter on macroinvertebrates and fish in boreal streams.2003In: Archiv für Hydrobiologie, ISSN 0003-9136, Vol. 157, p. 505–523-Article in journal (Refereed)
  • 63.
    Hoffsten, P.-O.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Morphometric variation, dispersal ability and distribution in adult caddisflies.Article in journal (Refereed)
  • 64.
    Hoffsten, P.-O.
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Malmqvist, B.
    Rarity and commonness in three perlodid stoneflies.Manuscript (Other academic)
  • 65.
    Hoffsten, P.-O.
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Malmqvist, B.
    The macroinvertebrate fauna and hydrogeology of springs in central Sweden.2000In: Hydrobiologia, ISSN 0018-8158, Vol. 436, no 1-3, p. 91-104Article in journal (Refereed)
  • 66.
    Hylander, Kristoffer
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Living on the edge: effectiveness of buffer strips in protecting biodiversity on boreal riparian forests2004Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The objective of this thesis is to evaluate the ecological consequences of buffer strip retention on riparian and terrestrial biodiversity. Earlier studies on forest buffer strips have evaluated their effectiveness in relation to water quality and aquatic biota. However, forests along streams are species rich habitats for many organism groups. Buffer strip management is assumed to be important also for protecting such species. Current approaches to biodiversity-oriented forest management practices need to be scientifically evaluated. In this thesis the effects on bryophytes and land snails have been evaluated.

    A before-and-after experiment along 15 small streams in northern Sweden showed that buffer strips of 10 m on each side of the stream moderated the negative effects exhibited at the clear-cuts. The number of land snail species remained similar as to before logging and the number of vanished bryophyte species was lower in the buffer strips than in the clear-cuts. The ground moisture influenced the survival rate of land snails at the clear-cuts. At mesic sites many species vanished but at wet sites the snail fauna was unaffected by the logging.

    Many bryophyte species, most of them liverworts, decreased or disappeared in the buffer strips. These were mostly growing on substrates elevated from the forest floor, such as logs, stumps and tree-bases. A number of nationally red-listed species, sensitive for changes in microclimate, were among those decreasing most. Thus, for the species in most need of protection the buffer strips were too narrow.

    An experiment with bryophyte transplants followed over a season showed that wet ground moisture moderated the negative edge effects in narrow buffer strips. On the other hand, the growth in mesic and moist sites was almost as low as in comparable clear-cuts.

    Microclimatic edge effects are stronger at south facing than north-facing edges of forest clear-cuts. This was shown in an experiment using bryophyte growth as an indicator of differences in microclimate. However, the depth of edge influence seemed to be similar between north- and south-facing forest edges, >30 m for one species. An explanation for this could be that wind penetrates deeper into edges than solar radiation and has a more variable direction.

    In conclusion, narrow buffer strips consist entirely of edge habitat. For many species the environment in buffer strips is good enough for persistence. For others, most notably bryophyte species on convex substrates, wider buffer strips are needed to ensure long-term survival.

  • 67.
    Hylander, Kristoffer
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    North- vs. south-facing edge effects: different magnitudes but equal spatial extentArticle in journal (Refereed)
  • 68.
    Hylander, Kristoffer
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Dynesius, Mats
    Jonsson, Bengt Gunnar
    Nilsson, Christer
    Lie low: substrate form determines the fate of bryophytes in riparian buffer stripsManuscript (preprint) (Other academic)
  • 69.
    Hylander, Kristoffer
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Jonsson, Bengt Gunnar
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Evaluating buffer strips along boreal streams using bryophtes as indicators2002In: Ecological Applications, ISSN 1051-0761, E-ISSN 1939-5582, Vol. 12, no 3, p. 797-806Article in journal (Refereed)
    Abstract [en]

    Buffer strips have recently become the main management practice for reducing logging impact on stream habitats in boreal and temperate regions. The habitat value of buffer strips, however, has not received much attention, although riparian forests belong to the systems with the highest biodiversity in these regions. We used plants as indicators of the ability of buffer strips to maintain an environment similar to intact riparian forests in a boreal forest landscape in northern Sweden. We measured the growth of three common bryophyte species (Hylocomiastrum umbratum, Calypogeia integristipula, and Tritomaria quinquedentata) transplanted to riparian habitat close to a stream in clear-cut logged sites 10-15 m wide buffer strips on each side of the stream, and intact (reference) sites. Each of the three site categories included six wet and six tnoist-mesic sites and the experiment was followed over three months in 1999. The species remained vital in the reference sites and grew substantially during the 3-mo-long experiment, but in the logged sites almost no growth was registered, and many shoots died (except for T. qninquedentata). The pattern was consistent irrespective of the ground moisture class. The performance of bryophytes in the moist-mesic buffer strips was almost as bad as in the logged sites, whereas in the wet buffer strips it was either intermediate between that in logged and reference sites (H. umbratum) or very similar to that in reference sites (C. integristipula and T. quinquedentata). The edge effect has previously been shown to vary depending on edge orientation, edge physiognomy, and weather conditions. We found that ground moisture can be of major importance as well. Although many buffer strips function better than no strips, 20-30 m wide strips (with a stream in the middle) through a logged area consist entirely of edge habitat. Increasing the buffer width and avoiding clear-cut logging on both sides of a watercourse would be the first steps to take for improving biodiversity conservation in riparian habitats. Our results also show that bryophytes are good indicators of habitat quality and efficient tools for assessing the ecological function of buffer strips.

  • 70.
    Hörnfeldt, Birger
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Cycles of voles, predators, and alternative prey in boreal Sweden1991Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Bank voles, grey-sided voles, and field voles had synchronous 3-4 year density cycles with variable amplitudes which averaged about 200-fold in each species. Cycles of vole predators (red fox and Tengmalm's owl), and their (foxes') alternative prey (mountain hare and forest grouse) lagged behind the vole cycles.

    The nomadic Tengmalm's owl responded with a very rapid and strong numerical increase to the initial cyclic summer increase of voles (the owl’s staple food). Owl breeding densities in the springs were highly correlated with vole supply in the previous autumns. This suggested that the number of breeding owls was largely determined in the autumn at the time of the owl's nomadic migrations, and that immigration was crucial for the rapid rise in owl numbers. The owl's numerical response was reinforced by the laying of earlier and larger clutches when food was plentiful. In addition, the owl has an early maturation at one year of age.

    The transition between subsequent vole cycles was characterized by a distinct shift in rate of change in numbers from low to high or markedly higher values in both summer and winter. Regulation increased progressively throughout the cycle since the rate of change decreased continuously in the summers. Moreover, there was a similar decrease of the rate of change in winter. Rate of change was delayed density-dependent. The delayed density-dependence had an 8 month time-lag in the summers and a 4 month time-lag in the winters relative to the density in previous autumns and springs, respectively. These findings suggest that vole cycles are likely to be generated by a time-lag mechanism. On theoretical grounds, it has been found that a delayed density- dependence of population growth rate with a 9 month time-lag caused stable limit cycles with a period between 3 and 4 years. Some mechanisms for the delayed density-dependence are suggested and discussed. The mechanisms are assumed to be related to remaining effects of vole populations past interactions with predators, food supplies, and/or diseases.

    Unlike the other voles, the bank vole had regular and distinct seasonal declines in density over winter. These declines are proposed to be due to predation, mainly by Tengmalm's owl. Supranivean foraging for epiphytic tree lichens and conifer seeds most likely explains why this species was frequently taken by the owl under snow-rich conditions.

    The alternative prey hypothesis predicts that a reduction of predator numbers should increase the number of alternative prey. Alternative prey should be less effectively synchronized to the vole cycle by predation at declining and low vole (main prey) densities; they may also lose their 3-4 year cyclicity. The appearance of sarcoptic mange among foxes in northern Sweden in the mid 1970s provided an opportunity to "test" these ideas, and these were found to be supported. In areas with highest mange infection rates, foxes declined markedly from the late 1970s to mid 1980s, whereas hare numbers rose rapidly and appeared non-cyclic.

  • 71.
    Johansson, Mats E.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Population biology of the clonal plant Ranunculus lingua1992Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The scope of this thesis was to identify, describe and quantify important life-history traits for the pseudoannual aquatic plant Ranunculus lingua in different ecological settings, by comparing populations from geographically marginal vs. central habitats.

    Results from a four-year field study showed that abiotic factors (water-level fluctuations and associated processes) tended to have a greater influence in marginal populations, whereas biotic factors (competition, insect grazing and fungal infections) dominated in central populations. This was reflected in different depth distribution of ramet numbers and ramet sizes between the areas, and In different dynamic patterns, with a higher flux of ramets in marginal populations.

    In a reciprocal transplant experiment, marginal ramets produced more but smaller rhizomes, whereas central ramets produced Individually larger but fewer rhizomes, irrespective of transplant site. A possible selection for genotypes producing large rhizomes in the central habitat was supported by the fact that initially smaller ramets were more likely to be diseased by the fungal pathogen Peronospora gigantea and damaged by insect grazing. In the marginal population, where density-independent mortality factors tend to dominate, a high reproductive output, expressed in production of high numbers of rhizomes, was suggested to be a favoured life-history trait.

    In a glasshouse experiment, ramets from marginal and central populations were grown in low and high densities and under three contrasting nutrient levels. The allocation to sexual structures was generally very low, and did not incur any costs in terms of reduced rhizome production. Rhizome production showed strong positive allometrical relationships to mother ramet size. Increasing mother ramet size resulted in a larger increase in rhizome numbers for the marginal than for the central population, whereas the increase in mean rhizome mass was more pronounced for the centred population. Both populations showed similar reductions in rhizome production in response to increased density and lowered nutrient levels, which could not be explained by size-dependent effects adone.

    The dispersal, dynamics and distribution of R. lingua were studied in a marginal river population in northern Sweden, where the only means of dispersal is by vegetative diaspores, i.e. floating rhizome fragments. Stranding occurred mainly in river curves and at obstacles, and the distribution of established stands was also highly correlated with these features. Relative changes in ramet numbers were correlated with water-level fluctuations during the present and previous growing seasons, with winter low-water, and with duration of spring-flood. The predictability of change was high within but low between stands. It was concluded that the patterns and mechanisms of dispersal are fundamental for local distribution patterns as well as variation in regional abundance in R. lingua

  • 72. Johnny, Berglund
    et al.
    Samuelsson, Kristina
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Muren, Umut
    Kull, Thomas
    Andersson, Agneta
    Simultaneous resource and predation limitation in the marine microbial food webManuscript (Other academic)
  • 73.
    Jonsson, B. G.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Nested plant and fungal communities: the importance of area and habitat quality in maximizing species capture in boreal old-growth forests2003In: Biological Conservation, Vol. 112, p. 319-328Article in journal (Refereed)
  • 74.
    Jonsson, Micael
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Effects of species richness on ecosystem function magnify with timeArticle in journal (Refereed)
  • 75.
    Jonsson, Micael
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Investigations of species richness effects on ecosystem functioning using stream-living macroinvertebrates as model organisms2003Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The work in this thesis deals with effects of changed species richness on process rates among stream-living macroinvertebrates. Global biodiversity is decreasing rapidly and it is poorly known what the consequences of this loss may be for ecosystems and the services they provide. Hence, it is important to investigate the potential effects of losing species. In streams, deforestation, introduction of non-native species, pollution and channelization are examples of events that may affect species richness negatively. In this thesis emphasis is on changes in species richness within functional feeding groups (FFGs) of stream-living macroinvertebrates. The FFGs used were shredding detritivores, grazers, filter feeders and predators - all of which uphold important ecological processes in streams. Along with an observational field study, species richness was manipulated in laboratory and field experiments to investigate the effects of changed species richness on process rates and thus ecosystem functioning.

    The results show that effects of changed species richness on process rates may be dramatic. Among the shredding detritivores there were negative effects on leaf mass loss, regardless whether fixed, random or predicted sequences of species loss was investigated. These effects could be attributed to either species richness per se or species composition. However, among the other FFGs the relationship between species richness and process rates was less consistent. In filter feeders, there was no or a negative effect of decreasing species richness while both grazers and predators showed positive effects of species loss.

    The results also show that the most important interactions between species in an experiment, thus potentially in a natural community, are likely to determine what the effect of species loss on process rates will be. Facilitation and niche differentiation lead to reduced process rates if species are lost, while mechanisms, such as interspecific resource or interference competition, produce the opposite effect. Furthermore, in systems with a diminishing resource, the first two mechanisms may become more important over time enhancing the effect of species loss in the long term.

    In conclusion, effects of species loss may be dramatically negative or positive even if lost species are classified as redundant. The effect in the short term most likely depends on which species are lost, on the original species composition and on the underlying mechanisms. Questions remaining to be answered are how important the observed effects are in more complex systems and if they are persistent over time? Future studies will tell.

  • 76.
    Jonsson, Micael
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Dangles, O
    Malmqvist, B.
    Guérold, F.
    Simulating species loss following perturbation: assessing the effects on process rates2002In: Proceedings of the Royal Society London B, Vol. 269, p. 1047-1052Article in journal (Refereed)
  • 77.
    Jonsson, Micael
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Malmqvist, B.
    Ecosystem process rate increases with animal species richness: evidence from leaf-eating, aquatic insects2000In: Oikos, Vol. 89, p. 519-523Article in journal (Refereed)
  • 78.
    Jonsson, Micael
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Malmqvist, B.
    Importance of species identity and number for process rates within stream macroinvertebrate functional feeding groups2003In: Journal of Animal Ecology, Vol. 72, p. 453-459Article in journal (Refereed)
  • 79.
    Jonsson, Micael
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Malmqvist, B.
    Hoffsten, P.-O.
    Leaf litter breakdown in boreal streams: does shredder species richness matter?2001In: Freshwater Biology, Vol. 46, p. 161-171Article in journal (Refereed)
  • 80. Kuuppo, Pirjo
    et al.
    Samuelsson, Kristina
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Lignell, Risto
    Seppälä, Jorma
    Tamminen, Timo
    Andersson, Agneta
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Umeå University, Faculty of Science and Technology, Umeå Marine Sciences Centre (UMF).
    Fate of increased production due to nutrient enrichment in late-summer plankton communities of the Baltic Proper2003In: Aquatic Microbial Ecology, ISSN 0948-3055, Vol. 32, no 1, p. 47-60Article in journal (Refereed)
  • 81.
    Leonardsson, Kjell
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Variation in age and size at maturation in two benthic crustaceans in the Gulf of Bothnia1990Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The thesis deals with variation in age and size at maturation in Saduria entomon and Pontoporeia affinis along a depth gradient in the Gulf of Bothnia, Sweden. I have analysed at what sizes and ages animals should mature in relation to growth and mortality conditions. The thesis also deals with predator-prey interactions within and between the two species.

    The isopod Saduria entomon matured during winter at an age of three years at 5 m depth in the Norrby archipelago (63° 30'N, 19° 50'E). Males matured eariier and at larger sizes (27-48 mm) than females (23-36 mm). The offspring were released in early summer. The adult size increased with increasing depth. Outside the archipelago, at 125 m depth, the sexes reached a size of 84 and 54 mm respectively. No evidence for temporal restriction in the release of the young was found at the deep area. The species was shown to have a high capacity for cannibalism on small conspecifics, although the small ones have the potential to avoid aggregations of large conspecifics. The number of small conspecifics eaten was related both to the absolute and relative densities of the alternative prey Pontoporeia affinis. The cannibalistic behaviour have the potential to act as a stabilizing mechanism in the Saduria-Pontoporeia system. Fourhom sculpin (Myoxocephalus quadricornis) was the fish species of utmost importance as a predator on S.entomon, and it mainly preferred large specimens.

    The amphipod Pontoporeia affinis matured at an age of two years in the littoral zone and at a very deep (210 m) locality. Between these depths it mainly reached maturation at an age of three years. In some years in densely populated areas, they delayed reproduction another year and reproduced as four year old. The variation in age at maturation in P.affinis in relation to depth could be quantitatively predicted by maximizing fitness in the Euler-Lotka equation.

    The size variation at maturation in S.entomon could be qualitatively predicted by maximizing fitness in the Euler-Lotka equation. The general condition for a smaller size at maturity to be adaptive at high temperatures (i.e. shallow areas) is that mortality rate should increase faster than growth rate with increasing temperature. When mortality is higher in young stages than in older and larger ones the pattern is also predicted when growth increases faster than mortality. Small animals may prefer warmer habitats than large ones, because of the presence of a size dependent trade-off between temperature induced growth and mortality. More exactly, the optimum solution of the trade-off between growth and mortality in hazardous environments was suggested to approach maximization of the expression s(W+g)/W, where s is survival rate, W is body weight, and g is growth rate.

  • 82.
    Lövgren, Johan
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Allochtonous input and cross- habitat foraging: impact on trophic interactions in a littoral food webArticle in journal (Refereed)
  • 83.
    Lövgren, Johan
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Food web dynamics in open and closed systems2004Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis is a summary of enclosure and microcosm experiments that aimed to study the impact of allochtonous subsidies on food web dynamics in a heterogeneous food web. In the enclosure studies, a three trophic level littoral food web was used. The food web consisted of two growth forms of primary producers: phytoplankton and periphyton and their associated herbivores: scraping and filtering herbivores. The predator used, YOY perch, affects both pathways in the food web. Manipulation of the openness for the different trophic levels showed that the inflow of phytoplankton and cross-habitat foraging by the herbivore level reinforced the compensatory response between the two growth forms of primary producers

    In the microcosm experiment, the response of an herbivore food web and a microbial community to inflow of resources and food web configuration was studied, using a model food web. The model food web consisted of two forms of primary producers, i.e. phytoplankton and periphyton, and two herbivores, i.e. Daphnia pulex feeding on phytoplankton, and Chydorus sphaericus feeding on both periphyton and phytoplankton. Three different food web configurations, all having the phytoplankton and periphyton, but either one of the herbivores, or both, were set up. The flow regimes consisted of an open treatment receiving a constant supply of phytoplankton, and a closed treatment with an initial resource pool. The effect of the inflow of phytoplankton was affected by the food web configuration. In the presence of D. pulex, the inflow of phytoplankton was made accessible to periphyton, and indirectly to C. sphaericus, which increased to such high densities that D. pulex was negatively affected. The inflow of phytoplankton had an indirect negative effect on the microbial community, since the biomass of herbivores increased, which imposed a higher grazing pressure on all parts of the microbial community.

  • 84.
    lövgren, Johan
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Bertolo, Andrea
    Persson, Lennart
    Flexible behavior at different trophic levels: impact on trophic dynamicsin a littoral food web.Manuscript (Other academic)
  • 85.
    Lövgren, Johan
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Persson, Lennart
    Fish mediated indirect effects in a littoral food web2002In: Oikos, ISSN 0030-1299, Vol. 96, no 1, p. 150-156Article in journal (Refereed)
  • 86.
    Lövgren, Johan
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Reinikainen, Marko
    Persson, Lennart
    Allochtonous input and trophic level heterogeneity: impact on an aquatic food webArticle in journal (Refereed)
  • 87.
    Malm Renöfält, Birgitta
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Vegetation patterns and processes in riparian landscapes2004Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The objective of this study was to increase understanding of the processes structuring and controlling the species richness of riparian plant communities. In particular, I examined the unimodal relationship, found in many rivers, between plant species richness and location along the river corridor. The most important finding was that this pattern is dynamic and varies with time, most likely in response to large-scale flood disturbances. I also found that the sensitivity to flood disturbance varied with the environmental setting of the riparian reaches. Turbulent sections of the river retained high species richness, whereas tranquil reaches had significantly lower species richness in years following high and prolonged flooding, compared to a period without extreme flood events. Riparian soils along turbulent reaches are more resistant to oxygen depletion during floods, a factor which is likely to contribute to the maintenance of species richness.

    The finding that the species richness pattern varied with time led me to ask which factors control plant diversity along riparian zones. I addressed this question by formulating three contrasting, although not mutually exclusive, hypotheses: (1) longitudinal patterns in riparian plant species richness are governed by local, river-related processes independent of the regional species richness, (2) riparian plant species richness is controlled by dispersal along the river, i.e., longitudinal control, and (3) the variation in riparian plant species richness mirrors variation in regional richness, i.e., lateral control. I found indications of all three types of control, although local factors seemed to fit most of the criteria. Riparian species richness was not significantly correlated to species richness in the surrounding upland valley. It was however significantly negatively correlated to soil pH, a local habitat factor of the reach. The fact that the species richness pattern varied in time, corresponding to the presence or absence of extreme flood events suggest that it is influenced by local disturbance regimes. The potential for control by longitudinal dispersal was found to be highest in the middle reaches of a river. Here, the similarity between upland and riparian vegetation was lowest, and invasibility (germination ability) was highest. Earlier work has shown that regulated rivers have an inverted species richness pattern compared to free-flowing rivers, with lowest species richness in the middle reaches. One potential mechanism behind this could be varying susceptibility to disturbance along the river. I tested this by experimentally disturbing the vegetation, applying the same level of disturbance along an entire free-flowing river. However, the response to experimental disturbance did not vary with location, likely because of a major flood disturbance preceding the experiment.

  • 88.
    Malm Renöfält, Birgitta
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Merritt, David
    Nilsson, Christer
    Connecting variation in vegetation and streamflow: the functions of large floods for riparian plant diversity and composition in boreal riversIn: Article in journal (Refereed)
  • 89.
    Malm Renöfält, Birgitta
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Nilsson, Christer
    Longitudinal variation in vegetation responses to disturbance in a riparian corridor along a boreal riverManuscript (Other academic)
  • 90.
    Malm Renöfält, Birgitta
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Nilsson, Christer
    Jansson, Roland
    Spatial and temporal patterns of species richness in a riparian landscapeIn: Article in journal (Refereed)
  • 91. Malmqvist, B.
    et al.
    Hoffsten, P.-O.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Macroinvertebrate taxonomic richness, community structure and nestedness in Swedish streams.2000In: Archiv für Hydrobiologie, ISSN 0003-9136, Vol. 150, p. 29-54Article in journal (Refereed)
  • 92.
    Nilsson, Christer
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Malm-Renöfält, Birgitta
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Linking flow Regime and water quality in rivers: a challenge to adaptive catchment management2008In: Ecology & society, ISSN 1708-3087, E-ISSN 1708-3087, Vol. 13, no 2, p. 18-Article in journal (Refereed)
    Abstract [en]

    Water quality describes the physicochemical characteristics of the water body. These vary naturally with the weather and with the spatiotemporal variation of the water flow, i.e., the flow regime. Worldwide, biota have adapted to the variation in these variables. River channels and their riparian zones contain a rich selection of adapted species and have been able to offer goods and services for sustaining human civilizations. Many human impacts on natural riverine environments have been destructive and present opportunities for rehabilitation. It is a big challenge to satisfy the needs of both humans and nature, without sacrificing one or the other. New ways of thinking, new policies, and institutional commitment are needed to make improvements, both in the ways water flow is modified in rivers by dam operations and direct extractions, and in the ways runoff from adjacent land is affected by land-use practices. Originally, prescribed flows were relatively static, but precepts have been developed to encompass variation, specifically on how water could be shared over the year to become most useful to ecosystems and humans. A key aspect is how allocations of water interact with physicochemical variation of water. An important applied question is how waste releases and discharge can be managed to reduce ecological and sanitary problems that might arise from inappropriate combinations of flow variation and physicochemical characteristics of water. We review knowledge in this field, provide examples on how the flow regime and the water quality can impact ecosystem processes, and conclude that most problems are associated with low-flow conditions. Given that reduced flows represent an escalating problem in an increasing number of rivers worldwide, managers are facing enormous challenges.

  • 93.
    Nilsson, Tina
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Polyandry and the evolution of reproductive divergence in insects2004Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Multiple mating by females is common in nature. Yet, the evolution and maintenance of polyandry remains a bit of an evolutionary puzzle. It was my aim in this thesis to reach a greater understanding of this phenomenon as well as to investigate the consequences of polyandry on the evolution of reproductive divergence in insects. In an extensive meta analysis addressing the direct effects of multiple mating on female fitness in insects, I found that insects gain from multiple matings in terms of increased lifetime offspring production. In species without nuptial feeding, increased mating rate leads to decreased female lifespan and my results strongly support the existence of an intermediate optimal female mating rate. However, results from an experimental study where I examined the relationship between female fitness and mating rate in the bean weevil (Callosobruchus maculatus) showed that female fitness was maximized at two alternative mating rates, indicating that some species may exhibit a more complex relationship between the costs and benefits of mating. In the meta analysis on species with nuptial feeding, I found only positive effects of increased mating rate and the puzzle is rather what constrains the actual mating rates of females in these groups.

    Sexual selection is a very potent driver of rapid evolutionary change in reproductive characters. Most research has focussed on precopulatory sexual selection, but in promiscuous species sexual selection continues after copulation and variance in male fertilization success gives rise to postcopulatory sexual selection. In this thesis I found that three allopatric populations of the red flour beetle (Tribolium castaneum) have diverged in traits related to reproduction. Male genotype affected all aspects of female reproduction, but more interestingly, males and females interacted in their effect on offspring production and reproductive rate, showing that the divergence was due to the evolution of both male and female reproductive traits.

    When studying postcopulatory sexual selection, sperm competition has been put forward as the main source of variance in fertilization success. The results from a set of double-mating experiments, using the same populations of flour beetles, provided strong evidence that cryptic female choice is also important in generating variance in male fertilization success. I found not only main effects of female genotype on male fertilization success but also male-female interactions which provide more unambiguous evidence for cryptic female choice. Finally, I attempted to uncover which male signals-female receptors are involved in the reproductive divergence observed in the Tribolium populations. In a double-mating experiment I manipulated female perception of two male reproductive signals, copulatory courtship and cuticular hydrocarbons, and the results indicate that, within populations, both signals are sexually selected. However, only male cuticular hydrocarbons seem to be involved in the reproductive divergence between the populations.

    In conclusion, multiple mating by female insects can be understood solely in terms of direct fitness benefits resulting from increased offspring production. I have shown that postcopulatory sexual selection can lead to rapid divergence in reproductive traits related to mating and that cryptic female choice plays an important role in this divergence.

  • 94.
    Nilsson, Tina
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Andres, José
    Postcopulatory sexual selection: the role of copulatory courtship and cuticular hydrocarbons in the reproductive divergence between two strains of the red flour beetleManuscript (Other academic)
  • 95.
    Nilsson, Tina
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Fricke, Claudia
    Arnqvist, Göran
    Patterns of divergence in the effects of malting on female reproductive performance in flour beetles2002In: Evolution, Vol. 56, no 1, p. 111-120Article in journal (Refereed)
  • 96.
    Nilsson, Tina
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Fricke, Claudia
    Arnqvist, Göran
    The effects of male and female genotype on variance in male fertilization success in the red flour beetle (Tribolium castaneum)2003In: Behavioral Ecology and Sociobiology, ISSN 0340-5443, Vol. 53, no 4, p. 227-233Article in journal (Refereed)
  • 97. Oksanen, Lauri
    et al.
    Aunapuu, Maano
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Oksanen, Tarja
    Schneider, Michael
    Ekerholm, Per
    Lundberg, Peter A.
    Armulik, Toomas
    Aruoja, Villem
    Bondestad, Lena
    Outlines of food webs in a low arctic tundra landscape in relation to three theories on trophic dynamics1997In: Multitrophic interactions in terrestrial systems, 1997, p. 351-373Chapter in book (Other academic)
  • 98.
    Oksanen, Tarja
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Predator-prey dynamics in small mammals along gradients of primary productivity1990Doctoral thesis, comprehensive summary (Other academic)
  • 99.
    Olofsson, Johan
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Dahlgren, Jonas
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Witzell, Johanna
    Gray-sided voles increase the susceptibility of northern willow, Salix glauca, to invertebrate herbivory2007In: Ecoscience, ISSN 1195-6860, Vol. 14, no 1, p. 48-54Article in journal (Refereed)
    Abstract [en]

    The relationships between grey-sided vole (Clethrionomys rufocanus) densities, levels of invertebrate herbivory on Northern willow (Salix glauca) leaves, and chemical quality of the willows was studied on 8 islands and 2 mainland sites with contrasting vole densities in northernmost Norway. These variables were measured at each of the study sites to determine the degree and nature of the effects of browsing-induced alterations in plant quality on subsequent invertebrate herbivory. The level of invertebrate herbivory was positively correlated with vole density, as were the number of leaves per shoot, leaf size, and leaf nitrogen content, while leaf C/N ratios were negatively correlated with vole density. The level of herbivory increased from > 1% on the vole-free island to < 4% on the island with the highest vole density. The plant character that explained most of the variance in the level of invertebrate herbivory was leaf size. Since the vole densities have been altered by human intervention and their numbers are largely governed by predation rather than food quality, the positive correlation between vole densities and level of invertebrate herbivory is probably due to a facilitative effect of voles on invertebrate herbivores, mediated through changes in plant chemistry. We suggest that voles affect susceptibility of willows to invertebrate herbivory both directly by winter browsing and indirectly by reducing the abundance of competing plants.

  • 100.
    Olsson, Katarina
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Population differentiation in Lythrum salicaria along a latitudinal gradient2004Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In this thesis, quantitative genetic approaches, common-garden experiments, and field studies were combined to examine patterns of population differentiation and the genetic architecture of characters of putative adaptive significance in the widely distributed perennial herb Lythrum salicaria. In this work, I (1) documented patterns of population differentiation in phenology, life-history, and morphology along latitudinal gradients at different geographical scales, (2) investigated the genetic architecture of phenology, flower morphology, and inflorescence size, and (3) combined estimates of phenotypic selection in the field with information on the genetic variance-covariance matrix (G) to examine potential constraints to adaptive evolution.

    A common-garden experiment demonstrated latitudinal variation in life-history, and phenology of growth and reproduction among L. salicaria populations sampled across Sweden. Flower morphology varied significantly among populations, but was, with the exception of calyx length, not related to latitude of origin. A second experiment, which included two Swedish, two Dutch, and two Spanish populations, indicated that the latitudinal gradient in reproductive and vegetative phenology might extend throughout Europe.

    A quantitative-genetic study of two Swedish populations revealed significant additive genetic variation for all phenological and morphological traits investigated. The G matrices of the populations differed significantly according to common principal component analysis, and genetic correlations within the study populations did not strictly correspond to trait correlations observed among populations.

    In a field study, I detected directional selection through female function for larger inflorescences in two consecutive years. Relative fitness increased disproportionately with inflorescence size in the year when supplemental hand-pollination indicated that pollen limitation was severe. Genetic correlations with inflorescence size considerably influenced predicted response to selection in other characters.

    Taken together, the results suggest that among-population differences in phenology and life-history in L. salicaria have evolved in response to latitudinal variation in length of the growing season. They demonstrate that the evolutionary potential of local populations may be considerable. The genetic covariance structure substantially influences predicted short-term evolutionary trajectories. However, the weak correspondence between genetic correlations documented within populations and trait correlations among populations, suggest that the G matrix has not imposed strict constraints on patterns of among-population differentiation.

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