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  • 1.
    Bergman, Eva
    et al.
    Karlstad University, Faculty of Social and Life Sciences, Department of Biology.
    Greenberg, Larry
    Karlstad University, Faculty of Social and Life Sciences, Department of Biology.
    Gustafsson, Pär
    Karlstad University, Faculty of Social and Life Sciences, Department of Biology.
    Gosselin, Marie-Pierre
    Karlstad University, Faculty of Social and Life Sciences, Department of Biology.
    Forest-stream linkages: Effects of woody debris on brown trout (Salmo trutta)2009Conference paper (Refereed)
  • 2.
    Calles, Olle
    et al.
    Karlstad University, Faculty of Social and Life Sciences, Department of Biology.
    Österling, Martin
    Karlstad University, Faculty of Social and Life Sciences, Department of Biology.
    Gustafsson, Pär
    Karlstad University, Faculty of Social and Life Sciences, Department of Biology.
    Nyberg, Lars
    Karlstad University, Faculty of Social and Life Sciences, Centre for Climate and Safety.
    Forsberg, Jan
    Karlstad University, Faculty of Technology and Science, Department of Energy, Environmental and Building Technology.
    Hebrand, M
    Olsson, M
    Renöfält, B
    Karlsson, H
    Johansson, M
    Biokanalers egenskaper och möjligheter2009Report (Other academic)
  • 3.
    Eros, Tibor
    et al.
    Karlstad University, Faculty of Social and Life Sciences, Department of Biology. Balaton Limnological Institute of the Hungarian Academy of Sciences, Hungary.
    Gustafsson, Pär
    Karlstad University, Faculty of Social and Life Sciences, Department of Biology.
    Greenberg, Larry
    Karlstad University, Faculty of Social and Life Sciences, Department of Biology.
    Bergman, Eva
    Karlstad University, Faculty of Social and Life Sciences, Department of Biology.
    Forest-Stream linkages: Effects of Terrestrial Invertebrate Input and Light on Diet and Growth of Brown Trout (Salmo trutta) in a Boreal Forest Stream2012In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 7, no 5, p. 1-11Article in journal (Refereed)
    Abstract [en]

    Subsidies of energy and material from the riparian zone have large impacts on recipient stream habitats. Human-induced changes, such as deforestation, may profoundly affect these pathways. However, the strength of individual factors on stream ecosystems is poorly understood since the factors involved often interact in complex ways. We isolated two of these factors, manipulating the flux of terrestrial input and the intensity of light in a 2 x 2 factorial design, where we followed the growth and diet of two size-classes of brown trout (Salmo trutta) and the development of periphyton, grazer macroinvertebrates, terrestrial invertebrate inputs, and drift in twelve 20 m long enclosed stream reaches in a five-monthlong experiment in a boreal coniferous forest stream. We found that light intensity, which was artificially increased 2.5 times above ambient levels, had an effect on grazer density, but no detectable effect on chlorophyll a biomass. We also found a seasonal effect on the amount of drift and that the reduction of terrestrial prey input, accomplished by covering enclosures with transparent plastic, had a negative impact on the amount of terrestrial invertebrates in the drift. Further, trout growth was strongly seasonal and followed the same pattern as drift biomass, and the reduction of terrestrial prey input had a negative effect on trout growth. Diet analysis was consistent with growth differences, showing that trout in open enclosures consumed relatively more terrestrial prey in summer than trout living in covered enclosures. We also predicted ontogenetic differences in the diet and growth of old and young trout, where we expected old fish to be more affected by the terrestrial prey reduction, but we found little evidence of ontogenetic differences. Overall, our results showed that reduced terrestrial prey inputs, as would be expected from forest harvesting, shaped differences in the growth and diet of the top predator, brown trout.

  • 4.
    Erős, Tibor
    et al.
    Balaton Limnological Research Institute of the Hungarian Academy of Sciences.
    Gustafsson, Pär
    Karlstad University, Faculty of Social and Life Sciences, Department of Biology.
    Greenberg, Larry A.
    Karlstad University, Faculty of Social and Life Sciences, Department of Biology.
    Bergman, Eva
    Karlstad University, Faculty of Social and Life Sciences, Department of Biology.
    Aquatic-terrestrial linkages: effects of terrestrial invertebrate input and light on a boreal stream communityManuscript (preprint) (Other academic)
  • 5.
    Gustafsson, Pär
    Karlstad University, Faculty of Social and Life Sciences, Department of Biology.
    Forest – stream linkages: Brown trout (Salmo trutta) responses to woody debris, terrestrial invertebrates and light2011Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Forests surrounding streams affect aquatic communities in numerous ways, contributing to energy fluxes between terrestrial and lotic ecosystems. The five papers in this thesis focus on woody debris, terrestrial invertebrates and light, three factors influenced by riparian zone structure, potentially affecting streams and brown trout (Salmo trutta). The individual strength of these stressors and their interactions with each other are not well studied, and their qualitative effects may differ both spatially and temporally as well as with the size-structure of specific fish populations.

    Using a combination of laboratory and field experiments, I examined the effects of woody debris, terrestrial invertebrates and light on prey availability and on the growth rates, diets and behavior of different size-classes of trout. My field experiments showed that addition of high densities of large wood affected trout growth in a positive way. This positive effect of large wood on trout growth may be related to prey abundance, as indicated by the high standing crop of aquatic macroinvertebrates on the wood. The positive effects on trout may also be related to decreased energy expenditures in wood habitats, as trout increased the ratio between numbers of prey captured and time spent active and that swimming activity and level of aggression decreased as wood densities were increased in a laboratory experiment. Terrestrial invertebrates are generally assumed to be a high quality prey resource for fish and my field experiments showed that reduction of terrestrial invertebrate inputs had a negative effect on trout growth. The availability of terrestrial prey in the stream was also coupled to trout diet and linked to growth, as fish with high growth rates had high proportions of terrestrial prey in their diets. Light, measured as PAR, did not have an effect on chlorophyll biomass, nor was there an effect on aquatic macroinvertebrates or trout. Hence, even if light levels were sufficient for increased photosynthesis, other factors such as low nutrient content may have limited the effects. Many of my results were dependent on fish-size. I observed, for example, that large trout had higher capture rates on surface-drifting terrestrial prey than small trout when prey densities were intermediate or high, but at low prey densities, the consumption of terrestrial prey by large and small trout were similar. Moreover, although large wood and terrestrial invertebrates affected growth of both small and large trout, the effects were generally more consistent for large trout.

    Although changes in riparian forests typically induce an array of interacting effects that certainly call for further research, the overall conclusion from this thesis is that many of the factors I have studied have profound effects on stream biota and trout. The positive effects from large wood also propose that adding trees to streams may partly compensate for negative effects associated with riparian deforestation.

  • 6. Gustafsson, Pär
    Forest-stream linkages: Experimental studies of foraging and growth of brown trout (Salmo trutta L)2008Licentiate thesis, monograph (Other academic)
  • 7.
    Gustafsson, Pär
    Karlstad University, Faculty of Social and Life Sciences, Department of Biology.
    Forest-stream linkages: Experimental studies of foraging and growth of brown trout (Salmo trutta L).2008Licentiate thesis, comprehensive summary (Other scientific)
    Abstract [en]

    Riparian vegetation along streams and rivers affects the aquatic community in numerous ways and often operates as a link for energy flux between forest and streams. The studies presented in this licentiate thesis focus on light and terrestrial invertebrates, two factors influenced by riparian zone structure, which potentially affect stream ecosystems and thus also brown trout (Salmo trutta). Paper I is a laboratory experiment where I study size dependent foraging behavior on surface-drifting terrestrial invertebrates and benthic invertebrates by brown trout. The results show a size-dependent difference in foraging ability with large trout being better able to use terrestrial surface prey than small trout. I argue that such ontogenetic foraging differences are due to both morphological constraints (eg. gape limitation) and size dependent behavioral differences related to predation risk. Paper II consists of a 5 month-long 2x2 factorial design field experiment where my objective was to examine the effects of terrestrial invertebrate input and solar radiation (PAR) on different trophic levels in a boreal headwater stream. More specifically, I followed the effects of increased light and decreased terrestrial invertebrate subsidies on periphyton, benthic macroinvertebrates and two size classes of the top fish predator, brown trout. The results showed that the reduction of terrestrial invertebrate input had size- and seasonal-dependent effects on trout, where large trout had lower growth rates than small trout, mainly in summer. Diet analyses of trout supported growth differences in that large trout in unmanipulated enclosures consumed relatively more terrestrial prey than large trout living in enclosures with reduced terrestrial inputs. A higher reliance on terrestrial prey subsidies by large trout compared to small may be explained by ontogenetic differences in foraging and habitat choice. Despite a 2.5-fold increase in PAR, light did not have an effect on chlorophyll a biomass, nor was there an effect on the density or composition of benthic macroinvertebrates. The lack of effects on primary production may be explained by very low nutrient levels in the stream.

  • 8.
    Gustafsson, Pär
    et al.
    Karlstad University, Faculty of Social and Life Sciences, Department of Biology.
    Bergman, Eva
    Karlstad University, Faculty of Social and Life Sciences, Department of Biology.
    Greenberg, Larry
    Karlstad University, Faculty of Social and Life Sciences, Department of Biology.
    Functional response and size-dependent foraging on aquatic and terrestrial prey by brown trout (Salmo trutta L.)2010In: Ecology of Freshwater Fish, ISSN 0906-6691, E-ISSN 1600-0633, Vol. 19, no 2, p. 170-177Article in journal (Refereed)
    Abstract [en]

    Terrestrial invertebrate subsidies are believed to be important energy sources for drift-feeding salmonids. Despite this, size-specific use of and efficiency in procuring this resource have not been studied to any great extent. Therefore, we measured the functional responses of three size classes of wild brown trout Salmo trutta (0+, 1+ and ≥2+) when fed either benthic- (Gammarus sp.) or surface-drifting prey (Musca domestica) in laboratory experiments. To test for size-specific prey preferences, both benthic and surface prey were presented simultaneously by presenting the fish with a constant density of benthic prey and a variable density of surface prey. The results showed that the functional response of 0+ trout differed significantly from the larger size classes, with 0+ fish having the lowest capture rates. Capture rates did not differ significantly between prey types. In experiments when both prey items were presented simultaneously, capture rate differed significantly between size classes, with larger trout having higher capture rates than smaller trout. However, capture rates within each size class did not change with prey density or prey composition. The two-prey experiments also showed that 1+ trout ate significantly more surface-drifting prey than 0+ trout. In contrast, there was no difference between 0+ and ≥2+ trout. Analyses of the vertical position of the fish in the water column corroborated size-specific foraging results: larger trout remained in the upper part of the water column between attacks on surface prey more often than smaller trout, which tended to seek refuge at the bottom between attacks. These size-specific differences in foraging and vertical position suggest that larger trout may be able to use surface-drifting prey to a greater extent than smaller conspecifics.

  • 9.
    Gustafsson, Pär
    et al.
    Karlstad University, Faculty of Social and Life Sciences, Department of Biology.
    Bergman, Eva
    Karlstad University, Faculty of Social and Life Sciences, Department of Biology.
    Greenberg, Larry
    Karlstad University, Faculty of Social and Life Sciences, Department of Biology.
    Erös, T
    Aquatic-terrestrial linkages: Effects of terrestrial invertebrate input and light on a boreal stream community2009Conference paper (Refereed)
  • 10.
    Gustafsson, Pär
    et al.
    Karlstad University, Faculty of Social and Life Sciences, Department of Biology.
    Greenberg, Larry A.
    Karlstad University, Faculty of Social and Life Sciences, Department of Biology.
    Bergman, Eva
    Karlstad University, Faculty of Social and Life Sciences, Department of Biology.
    Effects of large wood density on brown strout (Salmo trutta) behaviour in artificial streamsManuscript (preprint) (Other academic)
  • 11.
    Gustafsson, Pär
    et al.
    Karlstad University, Faculty of Social and Life Sciences, Department of Biology.
    Greenberg, Larry A.
    Karlstad University, Faculty of Social and Life Sciences, Department of Biology.
    Bergman, Eva
    Karlstad University, Faculty of Social and Life Sciences.
    Effects of woody debris and terrestrial invertebrates on the diet and growth of brown strout (Salmo trutta) in a boreal streamManuscript (preprint) (Other academic)
  • 12.
    Gustafsson, Pär
    et al.
    Karlstad University, Faculty of Social and Life Sciences, Department of Biology.
    Greenberg, Larry A.
    Karlstad University, Faculty of Social and Life Sciences, Department of Biology.
    Bergman, Eva
    Karlstad University, Faculty of Social and Life Sciences, Department of Biology.
    Influence of woody debris and terrestrial invertebrates on prey resources for stream living fishManuscript (preprint) (Other academic)
  • 13.
    Gustafsson, Pär
    et al.
    Karlstad University, Faculty of Social and Life Sciences, Department of Biology.
    Greenberg, Larry
    Karlstad University, Faculty of Social and Life Sciences, Department of Biology.
    Bergman, Eva
    Karlstad University, Faculty of Social and Life Sciences, Department of Biology.
    Effects of woody debris and the supply of terrestrial invertebrates on the diet and growth of brown trout (Salmo trutta) in a boreal stream2014In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 59, no 12, p. 2488-2501Article in journal (Refereed)
    Abstract [en]
    1. Changes to the riparian vegetation of forest streams during timber harvesting may have considerable impacts on stream biota, but few studies have attempted to separate the effects of individual factors that are altered during clear-felling operations.
    2. We studied the effects of large wood and terrestrial invertebrate supply, two factors affected by forest harvesting, on the growth and diet of two size classes of brown trout (Salmo trutta) during a two-month (June–August) field enclosure experiment. Twelve 20-m-long enclosed stream reaches were used in a 2 × 2 factorial design, with large wood either absent or added to mimic pre-modern forestry conditions, and terrestrial invertebrate inputs either reduced or maintained at ambient levels.
    3. The addition of large wood had a positive effect on the growth of large trout but no effect on small trout, whereas terrestrial invertebrate input had no effect on the growth of either size class. Growth rates were highest in the treatment with ambient terrestrial invertebrate inputs and added wood, were lowest in the treatment with reduced terrestrial invertebrate inputs and no added wood and were intermediate in the other two treatments.
    4. Dietary analyses showed no difference in treatments with and without added wood, perhaps because instream wood influences growth by producing profitable stream positions for trout, rather than by acting as a source of prey. Terrestrial invertebrate inputs affected the diet, as trout in enclosures with reduced inputs had a lower proportion of terrestrial invertebrate biomass in the diet than trout in enclosures with ambient terrestrial inputs.
    5. Our results suggest that leaving woody debris in streams when harvesting forests may enhance trout growth and that this is probably due to the physical changes in depth and current velocity caused by the wood rather than to changes in dietary prey composition.
  • 14.
    Gustafsson, Pär
    et al.
    Karlstad University, Faculty of Social and Life Sciences, Department of Biology.
    Greenberg, Larry
    Karlstad University, Faculty of Social and Life Sciences, Department of Biology.
    Bergman, Eva
    Karlstad University, Faculty of Social and Life Sciences, Department of Biology.
    Woody debris and terrestrial invertebrates: effects on prey resourses for brown trout (Salmo trutta) in a boreal stream2014In: Environmental Biology of Fishes, ISSN 0378-1909, E-ISSN 1573-5133, Vol. 97, no 5, p. 529-542Article in journal (Refereed)
    Abstract [en]

    Intensive forestry and other activities that alter riparian vegetation may disrupt the connectivity and the flux of energy between terrestrial and aquatic habitats and have large effects on biota, especially in small streams. We manipulated the amount of in-stream wood and the flux of terrestrial invertebrate subsidies to determine how these factors affected potential food resources for drift-feeding brown trout (Salmo trutta ) in a boreal Swedish forest stream. Specifically, we followed the effects on the abundance of aquatic and terrestrial invertebrate fauna from June to August 2007. The treatments were 1) addition of wood, unmanipulated terrestrial invertebrate inputs, 2) reduction of terrestrial invertebrate inputs (using canopy covers), no addition of wood, 3) unmanipulated ambient conditions, 4) simultaneous addition of wood and reduction of terrestrial invertebrate inputs. Added wood resulted in greater biomass of aquatic invertebrate biomass, and both input and drift of terrestrial invertebrates were reduced by canopy covers. In terms of total potential prey biomass, the addition of wood with ambient levels of terrestrial invertebrate inputs had the highest standing crop of benthic, wood-living and terrestrial invertebrates combined, whereas the treatment with reduced terrestrial input and no wood added had the lowest standing crop. Our study indicates that forest practices that both reduce the recruitment of wood and the input of terrestrial invertebrates to small streams have negative effects on prey availability for drift-feeding brown trout. The positive effects of wood addition on biomass of aquatic macroinvertebrates may partly compensate for the negative effects of reduced terrestrial invertebrate subsidies.

  • 15. Stickler, M.
    et al.
    Calles, Olle
    Karlstad University, Faculty of Social and Life Sciences, Department of Biology.
    Kiljunen, M.
    Fast Jensen, L.
    Sundt-Hansen, L.
    Gustafsson, Pär
    The 2nd Nordic Workshop for PhD students on Salmo salar and Salmo trutta Research2006Report (Refereed)
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