umu.sePublications
Change search
Refine search result
3456789 251 - 300 of 1290
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 251. De Long, Jonathan R.
    et al.
    Dorrepaal, Ellen
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Kardol, Paul
    Nilsson, Marie-Charlotte
    Teuber, Laurenz M.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Wardle, David A.
    Contrasting Responses of Soil Microbial and Nematode Communities to Warming and Plant Functional Group Removal Across a Post-fire Boreal Forest Successional Gradient2016In: Ecosystems (New York. Print), ISSN 1432-9840, E-ISSN 1435-0629, Vol. 19, no 2, p. 339-355Article in journal (Refereed)
    Abstract [en]

    Global warming is causing increases in surface temperatures and has the potential to influence the structure of soil microbial and faunal communities. However, little is known about how warming interacts with other ecosystem drivers, such as plant functional groups or changes associated with succession, to affect the soil community and thereby alter ecosystem functioning. We investigated how experimental warming and the removal of plant functional groups along a post-fire boreal forest successional gradient impacted soil microbial and nematode communities. Our results showed that warming altered soil microbial communities and favored bacterial-based microbial communities, but these effects were mediated by mosses and shrubs, and often varied with successional stage. Meanwhile, the nematode community was generally unaffected by warming and was positively affected by the presence of mosses and shrubs, with these effects mostly independent of successional stage. These results highlight that different groups of soil organisms may respond dissimilarly to interactions between warming and changes to plant functional groups, with likely consequences for ecosystem functioning that may vary with successional stage. Due to the ubiquitous presence of shrubs and mosses in boreal forests, the effects observed in this study are likely to be significant over a large proportion of the terrestrial land surface. Our results demonstrate that it is crucial to consider interactive effects between warming, plant functional groups, and successional stage when predicting soil community responses to global climate change in forested ecosystems.

  • 252. De Long, Jonathan R.
    et al.
    Dorrepaal, Ellen
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Kardol, Paul
    Nilsson, Marie-Charlotte
    Teuber, Laurenz M.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Wardle, David A.
    Understory plant functional groups and litter species identity are stronger drivers of litter decomposition than warming along a boreal forest post-fire successional gradient2016In: Soil Biology and Biochemistry, ISSN 0038-0717, E-ISSN 1879-3428, Vol. 98, p. 159-170Article in journal (Refereed)
    Abstract [en]

    Increasing surface temperatures due to climate change have the potential to alter plant litter mass loss and nutrient release during decomposition. However, a great deal of uncertainty remains concerning how ecosystem functioning may be affected by interactions between warming and other drivers, such as plant functional group composition and environmental context. In this study, we investigated how vascular plant litter decomposition and nutrient release were affected by experimental warming, moss removal and shrub removal along a post-fire boreal forest successional gradient. Our results show that litter decomposition and nutrient loss were primarily driven by understory plant functional group removal. The removal of mosses generally reduced litter mass loss and increased litter phosphorus (P) loss, while shrub removal typically increased litter mass loss and in one litter species reduced immobilization of P. Litter nitrogen (N) loss was unaffected by plant functional group removal. Warming interacted with successional stage and species identity of the litter decomposed, but these effects were uncommon and generally weak. As climate change advances, moss cover is expected to decrease, while shrub cover is expected to increase. Taken together with our results, this suggests that lower moss cover will decrease leaf litter decomposition rates and increase P release from litter, while increasing shrub cover will decrease decomposition rates and may reduce P release from litter. Our results demonstrate that in the short term, the direct effects of warming and successional stage will play a relatively minor role in driving litter decomposition processes in the boreal forest. In the long term, as the climate warms, temperature and its indirect effects via changes in the understory vegetation will play an important role in driving litter decomposition, thereby potentially altering C storage and nutrient cycling. 

  • 253. De Long, Jonathan R.
    et al.
    Kardol, Paul
    Sundqvist, Maja K.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Dept of Forest Ecology and Management, Swedish Univ. of Agricultural Sciences, Umeå, Sweden.
    Veen, G. F. (Ciska)
    Wardle, David A.
    Plant growth response to direct and indirect temperature effects varies by vegetation type and elevation in a subarctic tundra2015In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 124, no 6, p. 772-783Article in journal (Refereed)
    Abstract [en]

    There has been growing recent use of elevational gradients as tools for assessing effects of temperature changes on vegetation properties, because these gradients enable temperature effects to be considered over larger spatial and temporal scales than is possible through conventional experiments. While many studies have explored the direct effects of temperature, the indirect effects of temperature through its long-term influence on soil abiotic or biotic properties remain essentially unexplored. We performed two climate chamber experiments using soils from a subarctic elevational gradient in Abisko, Sweden to investigate the direct effects of temperature, and indirect effects of temperature via soil legacies, on growth of two grass species. The soils were collected from each of two vegetation types (heath, dominated by dwarf shrubs, and meadow, dominated by graminoids and herbs) at each of three elevations. We found that plants responded to both the direct effect of temperature and its indirect effect via soil legacies, and that direct and indirect effects were largely decoupled. Vegetation type was a major determinant of plant responses to both the direct and indirect effects of temperature; responses to soils from increasing elevation were stronger and showed a more linear decline for meadow than for heath soils. The influence of soil biota on plant growth was independent of elevation, with a positive influence across all elevations regardless of soil origin for meadow soils but not for heath soils. Taken together, this means that responses of plant growth to soil legacy effects of temperature across the elevational gradient were driven primarily by soil abiotic, and not biotic, factors. These findings emphasize that vegetation type is a strong determinant of how temperature variation across elevational gradients impacts on plant growth, and highlight the need for considering both direct and indirect effects of temperature on plant responses to future climate change.

  • 254. De Long, Jonathan R.
    et al.
    Laudon, Hjalmar
    Blume-Werry, Gesche
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Kardol, Paul
    Nematode community resistant to deep soil frost in boreal forest soils2016In: Pedobiologia, ISSN 0031-4056, E-ISSN 1873-1511, Vol. 59, no 5-6, p. 243-251Article in journal (Refereed)
    Abstract [en]

    As global climate change advances, shifts in winter precipitation are becoming more common in high latitude ecosystems, resulting in less insulating snow cover and deeper soil frost. Long-term alterations to soil frost can impact on ecosystem processes such as decomposition, microbial activity and vegetation dynamics. In this study we utilized the longest running, well-characterized soil frost manipulation experiment in a boreal forest. We measured nematode family composition and feeding group abundances at four different soil layer depths from plots that had been subjected to deep soil frost for one and 11 years. The overall abundance of nematodes and the different feeding groups were unaffected by deep soil frost. However, a higher Maturity Index was weakly associated with deep soil frost (indicative of lower nutrient enrichment and more persister nematode (i.e., K-strategist) families), likely due to the loss of nutrients and reduced inputs from inhibited decomposition. Multivariate and regression analyses showed that most nematode families were weakly associated with dominant understory plant species and strongly associated with soil organic matter (SOM). This is probably the result of higher resource availability in the control plots, which is favorable to the nematode community. These results indicate that the nematode community was more strongly driven by the long-term indirect effects of deep soil frost on SOM as opposed to the direct effects. Our findings highlight that the indirect effects of altered winter precipitation and soil frost patterns may be more important than direct winter climate effects. Further, such indirect effects on SOM and the plant community that may affect the nematode community can only be seen in long-term experiments. Finally, given the critical role nematodes play in soil food webs and carbon and nutrient cycling, our results demonstrate the necessity of considering the response of nematodes to global climate change in boreal forest soils. 

  • 255. de Roos, A. M.
    et al.
    Persson, Lennart
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Population and community ecology of ontogenetic development2013Book (Other academic)
    Abstract [en]

    Most organisms show substantial changes in size or morphology after they become independent of their parents and have to find their own food. Furthermore, the rate at which these changes occur generally depends on the amount of food they ingest. In this book, André de Roos and Lennart Persson advance a synthetic and individual-based theory of the effects of this plastic ontogenetic development on the dynamics of populations and communities. De Roos and Persson show how the effects of ontogenetic development on ecological dynamics critically depend on the efficiency with which differently sized individuals convert food into new biomass. Differences in this efficiency--or ontogenetic asymmetry--lead to bottlenecks in and thus population regulation by either maturation or reproduction. De Roos and Persson investigate the community consequences of these bottlenecks for trophic configurations that vary in the number and type of interacting species and in the degree of ontogenetic niche shifts exhibited by their individuals. They also demonstrate how insights into the effects of maturation and reproduction limitation on community equilibrium carry over to the dynamics of size-structured populations and give rise to different types of cohort-driven cycles.

  • 256. De Ruyck, Chris
    et al.
    Hobson, Keith A.
    Koper, Nicola
    Larson, Keith W.
    Wassenaar, Leonard I.
    An Appraisal of the Use of Hydrogen-Isotope Methods to Delineate Origins of Migratory Saw-whet Owls in North America2013In: The Condor, ISSN 00105422, 1938-5129, Vol. 115, no 2, p. 366-374Article in journal (Refereed)
  • 257. Decker, Vicki Huizu Guo
    et al.
    Bandau, Franziska
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Gundale, Michael J.
    Cole, Christopher
    Albrectsen, Benedicte Riber
    Genetic variation of foliar tannins determines how soil nitrogen impacts phenylpropanoid pathway regulation in aspenArticle in journal (Other academic)
  • 258. Declerck, Steven A. J.
    et al.
    Malo, Andrea R.
    Diehl, Sebastian
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Waasdorp, Dennis
    Lemmen, Kimberley D.
    Proios, Konstantinos
    Papakostas, Spiros
    Rapid adaptation of herbivore consumers to nutrient limitation: eco-evolutionary feedbacks to population demography and resource control2015In: Ecology Letters, ISSN 1461-023X, E-ISSN 1461-0248, Vol. 18, no 6, p. 553-562Article in journal (Refereed)
    Abstract [en]

    Humans alter biogeochemical cycles of essential elements such as phosphorus (P). Prediction of ecosystem consequences of altered elemental cycles requires integration of ecology, evolutionary biology and the framework of ecological stoichiometry. We studied micro-evolutionary responses of a herbivorous rotifer to P-limited food and the potential consequences for its population demography and for ecosystem properties. We subjected field-derived, replicate rotifer populations to P-deficient and P-replete algal food, and studied adaptation in common garden transplant experiments after 103 and 209days of selection. When fed P-limited food, populations with a P-limitation selection history suffered 37% lower mortality, reached twice the steady state biomass, and reduced algae by 40% compared to populations with a P-replete selection history. Adaptation involved no change in rotifer elemental composition but reduced investment in sex. This study demonstrates potentially strong eco-evolutionary feedbacks from shifting elemental balances to ecosystem properties, including grazing pressure and the ratio of grazer:producer biomass.

  • 259.
    Degerman, Rickard
    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).
    Response of marine food webs to climate-induced changes in temperature and inflow of allochthonous organic matter2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Global records of temperature show a warming trend both in the atmosphere and in the oceans. Current climate change scenarios indicate that global temperature will continue to increase in the future. The effects will however be very different in different geographic regions. In northern Europe precipitation is projected to increase along with temperature. Increased precipitation will lead to higher river discharge to the Baltic Sea, which will be accompanied by higher inflow of allochthonous organic matter (ADOM) from the terrestrial system. Both changes in temperature and ADOM may affect community composition, altering the ratio between heterotrophic and autotrophic organisms. Climate changes may thus have severe and complex effects in the Baltic Sea, which has low species diversity and is highly vulnerable to environmental change. The aim of my thesis was to acquire a conceptual understanding of aquatic food web responses to increased temperature and inputs of ADOM. These factors were chosen to reflect plausible climate change scenarios. I performed microcosm and mesocosm experiments as well as a theoretical modeling study. My studies had a holistic approach as they covered entire food webs, from bacteria and phytoplankton to planktivorous fish. The results indicate a strong positive effect of increased temperature and ADOM input on the bacterial community and the microbial food web. However, at the prevailing naturally low nutrient concentrations in the Baltic Sea, the effect of increased temperature may be hampered by nutrient deficiency. In general my results show that inputs of ADOM will cause an increase of the bacterial production. This in turn can negatively affect the production at higher trophic levels, due to establishment of an intermediate trophic level, consisting of protozoa. However, the described effects can be counteracted by a number of factors, as for example the relatively high temperature optimum of fish, which will lead to a more efficient exploitation of the system. Furthermore, the length of the food web was observed to be a strong regulating factor for food web responses and ecosystem functioning. Hence, the effect of environmental changes may differ quite drastically depending on the number of trophic levels and community composition of the system. The results of my thesis are of importance as they predict possible ecological consequences of climate change, and as they also demonstrate that variables cannot be examined separately.

  • 260.
    Degerman, Rickard
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Using bioindicators to identify past fish introductions in Swedish mountain lakes - paleolimnic study2006Independent thesis Advanced level (degree of Master (One Year)), 20 credits / 30 HE creditsStudent thesis
  • 261.
    Degerman, Rickard
    et al.
    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).
    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).
    Modelling effects of river inflow of allochthonous dissolved organic carbon on coastal productionManuscript (preprint) (Other academic)
  • 262.
    Degerman, Rickard
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Dinasquet, Julie
    Kalmar, Sweden.
    Riemann, Lasse
    Kalmar, Sweden; Helsingör, Denmark.
    de Luna, Sara Sjostedt
    Umeå University, Faculty of Science and Technology, Department of Mathematics and Mathematical Statistics.
    Andersson, Agneta
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Effect of resource availability on bacterial community responses to increased temperature2013In: Aquatic Microbial Ecology, ISSN 0948-3055, E-ISSN 1616-1564, Vol. 68, no 2, p. 131-142Article in journal (Refereed)
    Abstract [en]

    Climate change is predicted to cause higher temperatures and increased precipitation, resulting in increased inflow of nutrients to coastal waters in northern Europe. This has been assumed to increase the overall heterotrophy, including enhanced bacterial growth. However, the relative importance of temperature, resource availability and bacterial community composition for the bacterial growth response is poorly understood. In the present study, we investigated effects of increased temperature on bacterial growth in waters supplemented with different nutrient concentrations and inoculated with microbial communities from distinct seasonal periods. Seven experiments were performed in the northern Baltic Sea spanning an entire annual cycle. In each experiment, bacterioplankton were exposed to 2 temperature regimes (in situ and in situ + 4 degrees C) and 5 nutrient concentrations. Generally, elevated temperature and higher nutrient levels caused an increase in the bacterial growth rate and a shortening of the response time (lag phase). However, at the lowest nutrient concentration, bacterial growth was low at all tested temperatures, implying a stronger dependence on resource availability than on temperature for bacterial growth. Furthermore, data indicated that different bacterial assemblages had varying temperature responses and that community composition was strongly affected by the combination of high nutrient addition and high temperature. These results support the concern that climate change will promote heterotrophy in aquatic systems, where nutrient levels will increase considerably. In such environments, the bacterial community composition will change, their growth rates will increase, and their response time will be shortened compared to the present situation.

  • 263.
    Degerman, Rickard
    et al.
    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).
    Lefébure, Robert
    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).
    Byström, Pär
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Båmstedt, Ulf
    Umeå University, Faculty of Science and Technology, Umeå Marine Sciences Centre (UMF). Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Larsson, Stefan
    Umeå University, Faculty of Science and Technology, Umeå Marine Sciences Centre (UMF). Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    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).
    Food web interactions determine energy transfer efficiency and top consumer responses to inputs of dissolved organic carbon2018In: Hydrobiologia, ISSN 0018-8158, E-ISSN 1573-5117, Vol. 805, no 1, p. 131-146Article in journal (Refereed)
    Abstract [en]

    Climate change projections indicate increased precipitation in northern Europe, leading to increased inflow of allochthonous organic matter to aquatic systems. The food web responses are poorly known, and may differ depending on the trophic structure. We performed an experimental mesocosm study where effects of labile dissolved organic carbon (DOC) on two different pelagic food webs were investigated, one having zooplankton as highest trophic level and the other with planktivorous fish as top consumer. In both food webs, DOC caused higher bacterial production and lower food web efficiency, i.e., energy transfer efficiency from the base to the top of the food web. However, the top-level response to DOC addition differed in the zooplankton and the fish systems. The zooplankton production increased due to efficient channeling of energy via both the bacteria land the phytoplankton pathway, while the fish production decreased due to channeling of energy mainly via the longer and less efficient bacterial pathway. We conclude that the added DOC either acted as a subsidy by increasing the production of the top trophic level (mesozooplankton), or as a sink causing decreased top consumer production (planktivorous fish).

  • 264.
    Degerman, Rickard
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Lefébure, Robert
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Byström, Pär
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Båmstedt, Ulf
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Larsson, Stefan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Eriksson, Lars-Ove
    Dept. of Wildlife, Fish and Environmental Studies, SLU.
    Andersson, Agneta
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Bottom-up and top-down control of pelagic food web efficienciesManuscript (preprint) (Other academic)
  • 265.
    Deininger, Anne
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Effects of inorganic nitrogen and organic carbon on pelagic food webs in boreal lakes2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Anthropogenic activities are increasing inorganic nitrogen (N) loadings to lakes in the northern hemisphere. In many boreal lakes phytoplankton are N limited, wherefore enhanced N input may affect the productivity of pelagic food webs. Simultaneously, global change causes increased inflows of terrestrial dissolved organic carbon (DOC) to boreal lakes. Between clear and humic lakes, whole lake primary and consumer production naturally differs. However, research is inconclusive as to what controls pelagic production in these lakes. Further, it is unclear how DOC affects the response of the pelagic food web to enhanced inorganic N availability. The overarching goal of this thesis was to study the effects of inorganic N and organic C for pelagic food webs in boreal lakes. In the thesis, I first identified the main drivers of pelagic production during summer in eight non-manipulated Swedish boreal lakes with naturally low or high DOC. Then I investigated how increased N availability affects the pelagic food chain, and how the response differs with DOC. Therefore, whole lake inorganic N fertilization experiments were conducted in six Swedish boreal lakes across a DOC gradient (low, medium, high) divided into three lake pairs (control, N enriched) with one reference and two impact years. In each lake, I also investigated the response of zooplankton growth using in situ mesocosm experiments excluding planktivores. I found that humic boreal lakes had lower phytoplankton production and biomass than clear water lakes. Further, phytoplankton community composition and food quality differed with DOC. However, high DOC did not reduce pelagic energy mobilization or zooplankton biomass, but promoted a higher dominance of cladoceran relative to copepod species. N addition clearly enhanced phytoplankton biomass and production in the experimental lakes. However, this stimulating N effect decreased with DOC as caused by light limitation. Further, the newly available phytoplankton energy derived from N addition was not efficiently transferred to zooplankton, which indicates a mismatch between producer energy supply and consumer energy use. Indeed, the mesocosm experiment revealed that decreased food quality of phytoplankton in response to N addition resulted in reduced food web performance, especially in clearer lakes. In humic lakes, zooplankton production and food web efficiency were clearly more resilient to N addition. In summary, my thesis suggests that any change in the landscape that enhances inorganic N availability will especially affect pelagic food webs in clear water lakes. In contrast, brownification will result in more lakes being resilient to eutrophication caused by enhanced N deposition.

  • 266.
    Deininger, Anne
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Faithfull, Carolyn
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Bergström, Ann-Kristin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Nitrogen effects on the pelagic food web are modified by dissolved organic carbon2017In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 184, no 4, p. 901-916Article in journal (Refereed)
    Abstract [en]

    Global environmental change has altered the nitrogen (N) cycle and enhanced terrestrial dissolved organic carbon (DOC) loadings to northern boreal lakes. However, it is still unclear how enhanced N availability affects pelagic food web efficiency (FWE) and crustacean zooplankton growth in N limited boreal lakes. Here, we performed in situ mesocosm experiments in six unproductive boreal Swedish lakes, paired across a DOC gradient, with one lake in each pair fertilized with N (2011: reference year; 2012, 2013: impact years). We assessed how zooplankton growth and FWE were affected by changes in pelagic energy mobilization (PEM), food chain length (phytoplankton versus bacterial production based food chain, i.e. PP:BP), and food quality (seston stoichiometry) in response to N fertilization. Although PP, PEM and PP:BP increased in low and medium DOC lakes after N fertilization, consumer growth and FWE were reduced, especially at low DOC-potentially due to reduced phytoplankton food quality [increased C: phosphorus (P); N:P]. At high DOC, N fertilization caused modest increases in PP and PEM, with marginal changes in PP:BP and phytoplankton food quality, which, combined, led to a slight increase in zooplankton growth and FWE. Consequently, at low DOC (<12 mg L-1), increased N availability lowers FWE due to mismatches in food quality demand and supply, whereas at high DOC this mismatch does not occur, and zooplankton production and FWE may increase. We conclude that the lake DOC level is critical for predicting the effects of enhanced inorganic N availability on pelagic productivity in boreal lakes.

  • 267.
    Deininger, Anne
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Faithfull, Carolyn L.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Bergström, Ann-Kristin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Nitrogen effects on aquatic food web efficiency in the pelagic zone of unproductive lakes along a gradient of dissolved organic carbonManuscript (preprint) (Other academic)
    Abstract [en]

    Atmospheric nitrogen (N) deposition and terrestrial dissolved organic carbon (DOC) loadings are increasing in northern boreal lakes. However, consequences of increased N availability on food web efficiency (FWE) and consumer growth in N limited unproductive boreal lakes are unclear. Here, we performed in situ mesocosm experiments in late summer (2011; 2013) in six unproductive boreal Swedish lakes, paired across a DOC gradient, with one lake in each pair fertilized with N (2011: reference year; 2012, 2013: impact years). We assessed how zooplankton growth and FWE were affected by changes in pelagic energy mobilization (PEM), food chain length (PP:BP, i.e. phytoplankton: bacterial production ratio), and food quality (seston stoichiometry) in response to N fertilization. Although PP, PEM and PP:BP increased in low and medium DOC lakes after N fertilization, consumer growth and FWE in the low DOC lake were reduced, potentially due to a reduction in phytoplankton food quality (increased C:P; N:P). At high DOC, N fertilization caused modest increases in PP and PEM, with marginal changes in PP:BP and phytoplankton food quality, which combined led to a slight increase in zooplankton growth and FWE. We conclude that the background lake DOC level is critical in order to infer effects of enhanced inorganic N availability on pelagic productivity and FWE. In clear lakes increased N deposition will decrease FWE due to mismatches in food quality demand and supply. In humic lakes this mismatch will not occur, wherefore and zooplankton production and FWE will increase slightly following enhanced N deposition.

  • 268.
    Deininger, Anne
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Faithfull, Carolyn L.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Bergström, Ann-Kristin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Phytoplankton response to whole lake inorganic N fertilization along a gradient in dissolved organic carbon2017In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 98, no 4, p. 982-994Article in journal (Refereed)
    Abstract [en]

    Global change has increased inorganic nitrogen (N) and dissolved organic carbon (DOC; i.e. ‘browning’) inputs to northern hemisphere boreal lakes. However, we do not know how phytoplankton in nutrient poor lake ecosystems of different DOC concentration respond to increased N availability. Here, we monitored changes in phytoplankton production, biomass and community composition in response to whole lake inorganic N fertilization in six boreal unproductive Swedish lakes divided into three lake pairs (control, N enriched) at three DOC levels (low, medium, high), with one reference year (2011) and two impact years (2012, 2013). We found that phytoplankton biomass and production decreased with DOC concentration before N fertilization. Further, phytoplankton community composition also differed with respect to DOC, with a dominance of non-flagellated autotrophs at low DOC towards an increasing dominance of flagellated autotrophs with increased lake DOC concentration. The N fertilization increased phytoplankton biomass and production in all lakes, but did not affect phytoplankton community composition. However, the net response in biomass and production to N fertilization declined with increasing DOC, implying that the lake DOC concentration is critical in order to infer phytoplankton responses to N fertilization, and that the system switches from being primarily nutrient limited to becoming increasingly light limited with increased DOC concentration. In conclusion, our results show that browning will reduce phytoplankton production and biomass and influence phytoplankton community composition, whereas increased inorganic N loadings from deposition, forestry or other land use will primarily enhance phytoplankton biomass and production. Together, any change in the landscape that enhances inorganic N availability will increase phytoplankton production and biomass, but the positive effects of N will be much weaker or even neutralized in browner lakes as caused by light limitation.

  • 269.
    Deininger, Anne
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Faithfull, Carolyn L.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Department of Oceanography, University of Hawai'i, Honolulu, USA.
    Karlsson, Jan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Klaus, Marcus
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Bergström, Ann-Kristin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Pelagic food web response to whole lake N fertilization2017In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 62, no 4, p. 1498-1511Article in journal (Refereed)
    Abstract [en]

    Anthropogenic activities are increasing inorganic nitrogen (N) loadings to unproductive boreal lakes. In many of these lakes phytoplankton are N limited, consequently N fertilization may affect ecosystem productivity and consumer resource use. Here, we conducted whole lake inorganic N fertilization experiments with six small N limited unproductive boreal lakes (three control and three N enriched) in an area receiving low N deposition with one reference and two impact years. Our aim was to assess the effects of N fertilization on pelagic biomass production and consumer resource use. We found that phytoplankton primary production (PP) and biomass, and the PP: bacterioplankton production ratio increased after fertilization. As expected, the relative contribution of phytoplankton derived resources (autochthony) that supported the crustacean zooplankton community increased. Yet, the response in the consumer community was modest with autochthony only increasing in one of the three major zooplankton groups and with no effect on zooplankton biomass. In conclusion, our findings imply that newly available phytoplankton energy derived from N fertilization was not efficiently transferred up to zooplankton, indicating a mismatch between producer energy supply and consumer energy use with potential accumulation of phytoplankton biomass as the result.

  • 270.
    Denfeld, Blaize A.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Baulch, Helen M.
    del Giorgio, Paul A.
    Hampton, Stephanie E.
    Karlsson, Jan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Climate Impacts Research Centre, Umeå University, Umeå, Sweden.
    A synthesis of carbon dioxide and methane dynamics during the ice-covered period of northern lakes2018In: Limnology and Oceanography Letters, ISSN 2378-2242, Vol. 3, no 3, p. 117-131Article in journal (Refereed)
    Abstract [en]

    The ice‐covered period on lakes in the northern hemisphere has often been neglected or assumed to have less importance relative to the open water season. However, recent studies challenge this convention, suggesting that the winter period is more dynamic than previously thought. In this review, we synthesize the current understanding of under‐ice carbon dioxide (CO2) and methane (CH4) dynamics, highlighting the annual importance of CO2 and CH4 emissions from lakes at ice‐melt. We compiled data from 25 studies that showed that the ice‐melt period represents 17% and 27% of the annual CO2 and CH4 emissions, respectively. We also found evidence that the magnitude and type of emission (i.e., CO2 and CH4) varies with characteristics of lakes including geographic location, lake morphometry, and physicochemical conditions. The scarcity of winter and spring carbon data from northern lakes represents a major gap in our understanding of annual budgets in these lakes and calls for future research during this key period.

  • 271.
    Denfeld, Blaize A.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Department of Ecology and Genetics/Limnology, Uppsala University, Uppsala, Sweden.
    Ricao Canelhas, Monica
    Weyhenmeyer, Gesa A.
    Bertilsson, Stefan
    Eiler, Alexander
    Bastviken, David
    Constraints on methane oxidation in ice-covered boreal lakes2016In: Journal of Geophysical Research - Biogeosciences, ISSN 2169-8953, E-ISSN 2169-8961, Vol. 121, no 7, p. 1924-1933Article in journal (Refereed)
    Abstract [en]

    Boreal lakes can be ice covered for a substantial portion of the year at which time methane (CH4) can accumulate below ice. The amount of CH4 emitted at ice melt is partially determined by the interplay between CH4 production and CH4 oxidation, performed by methane-oxidizing bacteria (MOB). Yet the balance between oxidation and emission and the potential for CH4 oxidation in various lakes during winter is largely unknown. To address this, we performed incubations at 2 degrees C to screen for wintertime CH4 oxidation potential in seven lakes. Results showed that CH4 oxidation was restricted to three lakes, where the phosphate concentrations were highest. Molecular analyses revealed that MOB were initially detected in all lakes, although an increase in type I MOB only occurred in the three lake water incubations where oxidation could be observed. Accordingly, the increase in CO2 was on average 5 times higher in these three lake water incubations. For one lake where no oxidation was measured, we tested if temperature and CH4 availability could trigger CH4 oxidation. However, regardless of incubation temperatures and CH4 concentrations, ranging from 2 to 20 degrees C and 1-500M, respectively, no oxidation was observed. Our study indicates that some lakes with active wintertime CH4 oxidation may have low emissions during ice melt, while other and particularly nutrient poor lakes may accumulate large amounts of CH4 below ice that, in the absence of CH4 oxidation, will be emitted following ice melt. This variability in CH4 oxidation rates between lakes needs to be accounted for in large-scale CH4 emission estimates.

  • 272.
    Despres, Laurence
    et al.
    Laboratoire d’Ecologie Alpine, CNRS-UMR 5553, Université J. Fourier.
    Cherif, Mehdi
    Biogéochimie et Ecologie des Milieux Continentaux Laboratory, Unité Mixte de Recherche 7618 Ecole Normale Supe´rieure.
    The role of competition in adaptive radiation: a field study on sequentially ovipositing host-specific seed predators2004In: Journal of Animal Ecology, ISSN 0021-8790, E-ISSN 1365-2656, Vol. 73, no 1, p. 109-116Article in journal (Refereed)
    Abstract [en]

    1. We propose an alternative model to the host-shifting model of sympatric speciation in plant-insect systems. The role of competition in driving ecological adaptive radiation was evaluated in a seed predator exploiting a single host-plant species. Sympatric speciation may occur through disruptive selection on oviposition timing if this shift decreases competition among larvae feeding on seeds. 2. The globeflower fly Chiastocheta presents a unique case of adaptive radiation, with at least six sister species co-developing in fruits of Trollius europaeus. These species all feed on seeds, and differ in their oviposition timing, one species ovipositing in 1-day-old flowers (early species), while all the other species sequentially oviposit throughout the flower life span (late species). We evaluated the impact of conspecific and heterospecific larvae on larval installation success, and on larval fresh mass and area, for early and late species, in natural conditions. 3. None of the three larval traits measured was correlated with fruit size, and no fruit lost all seeds to predation, suggesting that seed availability was not a limiting factor for larval development. 4. Our results show strong intraspecific competition among early larvae for larval installation, and among late larvae for larval mass. By contrast, larval competition between species was weak. These results are consistent with the hypothesis that shifts in oviposition promoted rapid radiation in globeflower flies by lowering competition among larvae.

  • 273.
    Dew, L. Alexander
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Monitoring and managing Chromolaena odorata in a South African savanna reserve: Evaluating the efficacy of current control programs in response to ecological factors and management protocols2015Independent thesis Advanced level (degree of Master (Two Years)), 40 credits / 60 HE creditsStudent thesis
    Abstract [en]

    Biological invasions have increased dramatically in the past centuries and are one of the greatest threats to biodiversity today. Invasions occur when organisms are introduced at a location to which they are non-native, and they reproduce and spread, causing damage to the environment. Chromolaena odorata, a herbaceous shrub from the Americas, is one of the most widespread and problematic invasive plant species in the tropics and sub-tropics. The plant is a serious problem in South Africa, where invasive species threaten the nation’s biodiversity and limited water supply. This study combined transect monitoring data of C. odorata with ecological and clearing management data to assess the efficacy of an invasive plant clearing program over its decade of operation in the Hluhluwe-iMfolozi reserve in KwaZulu-Natal, South Africa. Densities and local extent of the C. odorata invasion were significantly reduced during the period of operations of the clearing program. Seasonal effects impacted clearing efficacy, namely a reduction in efficacy during the seed dispersal period. Effort and fire frequency were positively associated with clearing success, and rainfall negatively associated with clearing success. Excluding the northern section of the reserve, where the invasion progressed over the whole landscape, observations of C. odorata were closer to watercourses than randomized points, indicating a water limitation for invasion in most of the park. Management implications drawn from the results include halting clearing during seed-drop months, giving extra attention to areas with more rainfall and other water availability, and incorporating fire with other clearing methods where possible. 

  • 274.
    Dibattista, Joseph D.
    et al.
    Redpath Museum and Department of Biology, McGill University, Montréal, Québec, Canada .
    Feldheim, Kevin A.
    Field Museum, Pritzker Laboratory for Molecular Systematics and Evolution, Chicago, IL, USA.
    Thibert-Plante, Xavier
    Redpath Museum and Department of Biology, McGill University, Montréal, Québec, Canada.
    Gruber, Samuel H.
    Division of Marine Biology and Fisheries, Rosenstiel School of Marine and Atmospheric Science, Miami, FL, USA.
    Hendry, Andrew P.
    Redpath Museum and Department of Biology, McGill University, Montréal, Québec, Canada.
    A genetic assessment of polyandry and breeding-site fidelity in lemon sharks2008In: Molecular Ecology, ISSN 0962-1083, E-ISSN 1365-294X, Vol. 17, no 14, p. 3337-3351Article in journal (Refereed)
    Abstract [en]

    We here employ 11 microsatellite markers and recently developed litter reconstruction methods to infer mating system parameters (i.e. polyandry and breeding-site fidelity) at a lemon shark nursery site in Marquesas Key, Florida. Four hundred and eight juvenile or subadult sharks were genotyped over eight complete breeding seasons. Using this information, we were able to infer family structure, as well as fully or partially reconstruct genotypes of 46 mothers and 163 fathers. Multiple litter reconstruction methods were used, and novel simulations helped define apparent bias and precision of at least some mating system parameters. For Marquesas Key, we find that adult female lemon sharks display high levels of polyandry (81% of all litters sampled) and stronger fidelity to the nursery site than do males. Indeed, few male sharks sired offspring from more than one litter during the course of the study. These findings were quite similar to previous results from another lemon shark nursery site (Bimini, Bahamas), suggesting conserved mating system parameters despite significant variation in early life-history traits (i.e. body size and growth) among sites. The finding of at least some site fidelity in females also supports the need for careful conservation of each nursery.

  • 275.
    Diehl, S.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    DIRECT AND INDIRECT EFFECTS OF OMNIVORY IN A LITTORAL LAKE COMMUNITY1995In: Ecology, Vol. 76, no 6, p. 1727-1740Article in journal (Refereed)
    Abstract [en]

    In spite of the ubiquity of omnivory in nature, its consequences for population dynamics have received little attention from theoretical and experimental ecologists. Having three direct consumer-resource links, three indirect numerical links, and a potential for indirect effects mediated by size structure and/or behavioral flexibility, a three-species omnivory system may exhibit complex population dynamics. In 2 x 3 m field enclosures in the littoral zone of a lake, I manipulated the dominating native benthivorous fish (greater than or equal to 2yr-old perch, Perca fluviatilis, omnivorous top consumer) and the dominating native benthic invertebrate predators (Sialis lutaria, Megaloptera, and odonates, intermediate consumers) in three gradients: increasing densities of perch in the near absence of Sialis and odonates, and increasing densities of Sialis and odonates in either the presence or absence of perch. The densities of their common prey (mainly chironomids) were left unmanipulated. Macroinvertebrate abundance, biomass, and size structure, as well as gut contents of perch and Sialis were sampled monthly over a 3-mo summer period. In the absence of perch, the experimental gradient of Sialis densities remained unchanged over time. In the presence of perch, Sialis decreased by about half at high initial densities, but remained unchanged at low initial densities. Perch also had a negative effect on odonates. In the near absence of Sialis and odonates, perch had a strong, negative effect on chironomids. Compared to enclosures without perch, chironomid abundance was strongly reduced at the lowest perch density, but leveled off with further increases in perch density. Sialis and odonates did not affect chironomid abundance when perch were absent. In contrast, chironomid abundance was positively affected by Sialis and odonates when perch were present. The overall effect of perch on chironomid abundance in the presence of Sialis and odonates was negative. The combined predatory and competitive effects of perch on Sialis and odonates raise the issue how Sialis and odonates coexist with perch. The lack of effect of perch on Sialis and chironomids at low densities of these prey suggests that prey refuges contribute significantly to their persistence in natural systems. The indirect positive effect of Sialis and odonates on chironomids indicates density dependence in per capita interaction coefficients and is most likely to be explained by a behavioral response of perch or chironomids to Sialis and odonates. I suggest that the theoretical and empirical investigation of model systems (such as three-component omnivory systems), which are sufficiently simple to be analytically and experimentally tractable, but still display a richness of common indirect effects, will contribute to our understanding of the dynamics of more complex food webs. Their study will benefit from experimental manipulations of more than one population at more than two densities.

  • 276.
    Diehl, S.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Paradoxes of enrichment: Effects of increased light versus nutrient supply on pelagic producer-grazer systems2007In: American Naturalist, Vol. 169, no 6, p. E173-E191Article in journal (Refereed)
    Abstract [en]

    Energy-based plant-herbivore models produce the "paradox of enrichment," a destabilizing influence of enrichment on population dynamics. Because many plants change their carbon : nutrient stoichiometry in response to the light : nutrient supply ratio, enrichment with light can cause a mismatch between the elemental compositions of plants and their herbivores. Herbivore growth rates may then decrease with increased light supply, which is termed the "paradox of energy enrichment." I present a stoichiometric phyto-plankton-grazer model that accounts for the dynamical vertical light gradient and explore how algal and grazer densities, mineral nutrient concentration, algal nutrient stoichiometry, and system stability respond to enrichment with light ( through changes in irradiance, background turbidity, and water column depth) versus enrichment with nutrients. Parameterized for Daphnia, the model produces several "unusual" phenomena: multiple equilibria ( with grazers extinct in spite of high algal biomass at one equilibrium), inconsistent light enrichment effects on stability ( light enrichment first destabilizes and then stabilizes), and the paradox of energy enrichment. These phenomena are restricted to the low end of realistic nutrient supplies except in very shallow systems, where high sedimentation rates effectively deplete the water column of nutrients. At higher nutrient supplies, light enrichment produces the classical paradox of enrichment, leading first to an increase in grazers at a stable equilibrium and then to algae-grazer oscillations.

  • 277.
    Diehl, S.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Phytoplankton, light, and nutrients in a gradient of mixing depths: Theory2002In: Ecology, Vol. 83, no 2, p. 386-398Article in journal (Refereed)
    Abstract [en]

    The depth of the well-mixed surface layer of lakes and oceans fundamentally affects phytoplankton populations. Specific nutrient supply, specific algal production, and specific sinking losses all decrease with increasing mixing depth. I use a dynamical model to investigate how phytoplankton biomass, light availability, and the distribution Of nutrients among various pools vary along a mixing depth gradient, and how the relationships of these variables to mixing depth depend on algal sinking velocity, abiotic light absorbents, nutrient enrichment, and the mode of nutrient supply (closed system with recycling vs. open system with external input). If phytoplankton is dominated by sinking algae, the primary causes of biomass limitation shift with increasing mixing depth from sinking loss limitation to nutrient limitation to light limitation. Consequently, algal biomass in the mixed layer (expressed per volume or area) and sedimented nutrients are unimodally related to mixing depth, whereas dissolved inorganic and total water column nutrients show the inverse pattern. Compared to closed systems, the maximum in the biomass concentration-mixing depth relationship occurs at much shallower depths in open systems without recycling of sedimented nutrients (such as mixed surface layers on top of stratified water columns). With increased algal sinking velocity, algal biomass decreases, and light penetration and dissolved nutrients both increase, whereas sedimented and total water column nutrients may increase or decrease. Increased abiotic turbidity reduces light penetration, algal biomass, and sedimented nutrients but increases dissolved and total water column nutrients. Finally, with nutrient enrichment, algal biomass and all nutrient compartments increase, whereas light penetration decreases. I use a graphical isocline approach to show that increasing external light supply, decreasing abiotic turbidity, and decreasing mixing depth represent three conceptually different forms of enrichment with light. Of those, decreasing abiotic turbidity is conceptually similar to enrichment with a mineral nutrient.

  • 278.
    Diehl, S.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    The evolution and maintenance of omnivory: Dynamic constraints and the role of food quality2003In: Ecology, Vol. 84, no 10, p. 2557-2567Article in journal (Refereed)
    Abstract [en]

    In several taxa, the ability to feed omnivorously from more than one trophic level has evolved from more specialized feeding habits. A prerequisite for this evolutionary scenario is initial coexistence (on the same or different trophic levels) of the consumers subsequently involved in omnivory. Evolution of omnivory should also be favored by prior asymmetries in consumer interactions. I use a dynamic model to explore conditions for coexistence of two consumers depending on a single biotic resource in simple. food webs of increasing asymmetry between consumers: (1) pure resource competition, (2) resource competition with unidirectional interference, (3) omnivory, and (4) pure predation. If consumers are energy limited, omnivory is unlikely to evolve from a competitive system, because stable coexistence of two consumers on a single resource is impossible, even if there is a trade-off between resource exploitation and interference abilities. Initial coexistence of two consumers is easier to achieve, if the species are arranged in a food chain. If costs of diet generalization are low, selection should then favor the inclusion of the resource in the top consumer's diet. In systems with high resource carrying capacity, the intermediate consumer will then, however, be frequently driven to extinction-in which case omnivory is not maintained. Low nutritional quality of the resource can stabilize the omnivory system and allow three-species coexistence at high resource carrying capacities. Low nutritional quality of the resource may also create conditions for the evolution of omnivory from a competitive system. If the content of an essential nutrient in resource biomass is dynamic, stable coexistence of two competitors becomes possible if both are limited by the nutrient content of the resource. In this case, selection may favor the, evolution of omnivory, because competitor biomass is usually of higher nutritional quality than resource biomass. An explicit treatment of flexible resource stoichiometry thus broadens the possibilities for the evolution of omnivory.

  • 279.
    Diehl, S.
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Berger, S.
    Ptacnik, R.
    Wild, A.
    Phytoplankton, light, and nutrients in a gradient of mixing depths: Field experiments2002In: Ecology, Vol. 83, no 2, p. 399-411Article in journal (Refereed)
    Abstract [en]

    We studied the effects of water column mixing depth and background turbidity on phytoplankton biomass, light climate, and nutrients in two field enclosure experiments designed to test, predictions of a dynamical model. In 1997 and 1998, we created gradients of mixing depth by enclosing the 100-mum-filtered phytoplankton community of a phosphorus-deficient lake in cylindrical plastic bags of varying depth (1.5-15 m) which were continuously mixed. To mimic different levels of background turbidity, we surrounded the transparent enclosure walls with a layer of opaque white (1997) or black (1998) plastic. The experiments were run for 4 wk (1997) and 6 wk (1998). The results supported two key assumptions of the model: specific production and specific sedimentation losses both decreased with increasing mixing depth. At all mixing depths, fast-sinking diatoms dominated (lie communities. In accordance with model predictions, algal biomass concentration and standing stock (summed over the mixed layer) showed a unimodal relationship to mixing depth when background turbidity was high (1998). When background turbidity was lower (1997), only the ascending limbs of the corresponding relationships were found, which support.,; the prediction that the mixing depth at which biomass peaks (i.e., becomes predominantly limited by light) increases with decreasing background turbidity. Also in accordance with predictions, light intensity at the bottom of the mixed layer decreased with increasing mixing depth and with increasing background turbidity. Finally, the data supported only the ascending limbs of the predicted inverse unimodal relationships among mixing depth and dissolved inorganic and total water column phosphorus. The absence of descending limbs in these relationships at low mixing depths was probably due to deviations of the experimental systems from two model assumptions. First, the remineralization rate of sedimented phosphorus may have been too slow to equilibrate with sedimentation losses over the experimental periods. Second, biomass yield per unit nutrient (the ratio of seston carbon to phosphorus) was not constant, but decreased with increasing mixing depth. To our knowledge, these are the first field experiments in which the effects of mixing depth on phytoplankton and its resources have been investigated systematically along a large gradient.

  • 280.
    Diehl, S.
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Berger, S.
    Wohrl, R.
    Flexible nutrient stoichiometry mediates environmental influences, on phytoplankton and its resources2005In: Ecology, Vol. 86, no 11, p. 2931-2945Article in journal (Refereed)
    Abstract [en]

    The elemental composition of plants, which affects ecosystem processes such as energy transfer to consumers and nutrient recycling, varies with the supply of nutrients and light. In contrast to most terrestrial systems, aquatic plants "compete" with abiotic light absorbents. Light supply to pelagic producers and, consequently, algal carbon to nutrient stoichiometry are therefore affected by background turbidity (light absorption by non-algal components, K-bg) and mixing depth (vertical extension of the mixed water column, z). Still, light as a dynamic variable has been neglected in models exploring the ecological consequences of flexible algal stoichiometry. In addition, there are hardly any field experiments exploring effects of light supply on planktonic systems. We present a dynamical model that accounts for the simultaneous dependence of algal production on light supply and internal algal nutrient stores and derive predictions on how a suite of state variables (algal biomass, light climate, algal nutrient stoichiometry, dissolved nutrient concentration, and nutrients in sediment) should be affected by z and K-bg. We compare these predictions with results of an enclosure experiment in a phosphorus-deficient lake, in which we manipulated z and K-bg. Algal biomass decreased at higher K-bg and showed a unimodal response to z (being limited by sinking losses at shallow z and by light at deep z). The biomass peak shifted toward lower z with increased K-bg. The seston carbon: phosphorus ratio decreased with increasing z and K-bg. Dissolved mineral phosphorus was undetectable in all treatments. Total water column phosphorus and sedimented phosphorus increased with increasing z but were unaffected by K-bg. These data are in almost complete qualitative congruence with model predictions over the examined range of mixing depths (1-15 m). The model thus provides a useful framework for the continued mechanistic exploration of how environmental drivers influence producer stoichiometry in pelagic environments.

  • 281.
    Diehl, S.
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Cooper, S. D.
    Kratz, K. W.
    Nisbet, R. M.
    Roll, S. K.
    Wiseman, S. W.
    Jenkins, T. M.
    Effects of multiple, predator-induced behaviors on short-term producer-grazer dynamics in open systems2000In: American Naturalist, Vol. 156, no 3, p. 293-313Article in journal (Refereed)
    Abstract [en]

    We investigated the population consequences of multiple behavioral responses of grazers to a foraging return-predation risk trade-off in an open system consisting of primary producers, grazers, and predators. Using a dynamical model where grazers adjust their foraging activity and emigration rate to the densities of predators and producers, we explored how changes in control variables (predator density, grazer immigration, and producer immigration and carrying capacity) affect the dynamics of producers and grazers at temporal scales shorter than consumer and predator reproduction. The model predicts that producer biomass increases and that both the density of foraging grazers and the feeding rate of predators decrease with predator density. These predictions hold although total (foraging + nonforaging) grazer density may actually increase with predator density. The latter will occur whenever the benefit of higher resource density outweighs the increased risk of predation. In this case. per capita grazer emigration decreases with predator density, which might be misinterpreted as a direct "freezing" response to predators. Increased grazer immigration is predicted to result in decreased producer density and increased densities of both foraging and total grazers, as well as increased grazer emigration and predator feeding rates. Increased producer immigration or carrying capacity should increase producer and grazer densities and predator feeding rate but decrease per capita grazer emigration. Manipulation of predator (trout) densities in a set of nine large (50 m(2)) stream channels produced results in broad agreement with model predictions. Most notably, a positive effect of trout on benthic algal biomass was mainly mediated through grazer behavior (changes in the use of epibenthic surfaces and in emigration rare) rather than through consumptive reductions of grazer numbers by trout.

  • 282.
    Diehl, S.
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Eklov, P.
    EFFECTS OF PISCIVORE-MEDIATED HABITAT USE ON RESOURCES, DIET, AND GROWTH OF PERCH1995In: Ecology, Vol. 76, no 6, p. 1712-1726Article in journal (Refereed)
    Abstract [en]

    We investigated experimentally how presence or absence of different piscivores influenced habitat use, diet, and individual growth of two size classes of juvenile perch (Perca fluviatilis) and abundances of juvenile perch resources in different habitats. Pond enclosures encompassed 3 X 6 m of dense vegetation and 9 X 6 m of open habitat, and were stocked with 75 young-of-year and 30 1-yr-old perch and with either three piscivorous perch, three northern pike (Esox lucius), or no piscivores. Northern pike were both larger and possessed a larger gape than piscivorous perch. To isolate behavioral responses of juvenile perch to piscivores, we replaced consumed young-of-year perch. Prey fish mortality was lowest without piscivores and highest with northern pike. Young-of-year perch increased their use of vegetation in the presence of both piscivores, whereas 1-yr-old perch increased their use of vegetation only with northern pike. For both age classes of prey fish, increased use of the vegetation led to reduced individual growth, owing to two complementary mechanisms. First, the physical complexity of submerged macrophytes likely interfered with the benthic feeding of perch, Second, increased use of the (relatively small) vegetated habitat increased the mean density experienced by prey fish. Piscivore-induced changes of prey fish densities in the two habitats had substantial effects on the biomass of prey fish resources in the open habitat, but only minor effects in the vegetation. Sialis lutaria, the major predatory macroinvertebrate (approximate to 50% of total macroinvertebrate biomass in the open habitat), and total predatory macroinvertebrates were positively affected by piscivores in the open habitat, but not in the vegetation. Chironomids (<3% of total macroinvertebrate biomass in the vegetation) and the sizes of nonpredatory macroinvertebrates were negatively affected by piscivores in the vegetation, but not in the open habitat. Biomass of nonpredatory macroinvertebrates, Cladocera, and Copepoda did not differ among treatments in either habitat. From our review of field experiments, vulnerable prey fish always change their habitat use in the presence of piscivores. Behaviorally mediated indirect effects of piscivores on individual growth rates and prey fish resources were just as frequently observed as direct effects of piscivores on prey fish survival.

  • 283.
    Diehl, S.
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Feissel, M.
    Effects of enrichment on three-level food chains with omnivory2000In: American Naturalist, Vol. 155, no 2, p. 200-218Article in journal (Refereed)
    Abstract [en]

    Although omnivory (the consumption of resources from more than one trophic level) is widespread, this fundamental limitation to the applicability of food chain theory to real communities has received only limited treatment. We investigated effects of enrichment (increasing carrying capacity, K, of the resource) on a system consisting of a resource (R), an intermediate consumer (N), and an omnivore (P) using a general mathematical model and tested the relevance of some of its predictions to a laboratory system of mixed bacteria (=R) and the ciliates Tetrahymena (=N) and Blepharisma (=P). The model produced six major predictions. First, N may facilitate or inhibit P. Enrichment may revert the net effect of N on P from facilitation to inhibition. Second, along a gradient of K, up to four regions of invasibility and stable coexistence of N and P may exist. At the lowest K, only R is present. At somewhat higher K, N can coexist with R. At intermediate it, either N and P coexist, or either consumer excludes the other clef ending on initial conditions. At the highest K, N may be excluded through apparent competition and only R and P can coexist. The pattern of persistence of Tetrahymena and Blepharisma along an enrichment gradient conformed fairly well to the scenario allowing coexistence at intermediate K. Third, fur stable equilibria of the omnivory system, R always increases and N always decreases with R. The abundances of bacteria and Tetrahymena were suggestive of such a pattern but did not allow a strict test because coexistence occurred at only one level of enrichment. Fourth, an omnivore can invade an R-N system at a lower K than an otherwise identical specialist predator of N. Fifth, an omnivore can always invade a food chain with such a specialist predator. Sixth, over ranges of K where both omnivory systems and otherwise identical three-level food chains are feasible, N is always less abundant in the omnivory system, whereas the relative abundances of R and P in omnivory systems compared to food chains may change with K. It is thus possible that total community biomass at a given It is lower in an omnivory system than in a food chain. Both the model and the experimental results caution that patterns of trophic-level abundances in response to enrichment predicted by food chain theory are not to be expected in systems with significant omnivory.

  • 284.
    Diehl, S.
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Feissel, M.
    Intraguild prey suffer from enrichment of their resources: A microcosm experiment with ciliates2001In: Ecology, Vol. 82, no 11, p. 2977-2983Article in journal (Refereed)
    Abstract [en]

    Predation among species that compete for resources is widespread. Theory suggests a counterintuitive consequence of such intraguild predation: enrichment of the shared resource, for which the intraguild prey must be the superior competitor, reduces the population size of the intraguild prey and may even cause its extinction. Experiments with bacteria (shared resource) and the ciliates Tetrahymena (intraguild prey) and Blepharisma (intraguild predator) confirmed these expectations. Tetrahymena was the better resource competitor. Grown separately, it persisted at lower levels of enrichment and drove bacterial densities to lower levels than did Blepharisma. When grown together with Blepharisma, Tetrahymena declined in density with increasing enrichment, whereas bacteria and Blepharisma increased. The data thus support the theoretically suggested mechanism as the cause of this pattern: with enrichment, increasing densities of bacteria sustained an increasing predation pressure from Blepharisma on Tetrahymena, which overrode the direct positive effect of bacteria as a food source of Tetrahymena. Generalizing from these results, we speculate that staggered invasions of omnivores followed by extinctions of intermediate prey should contribute to the frequently observed unimodal or neutral responses of species richness and food chain length to increasing productivity.

  • 285.
    Diehl, S.
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Kornijow, R.
    Influence of submerged macrophytes on trophic interactions among fish and macroinvertebrates1998In: Structuring Role of Subbmerged Macrophytes in Lakes, 1998Chapter in book (Other (popular science, discussion, etc.))
  • 286.
    Diehl, Sebastian
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Effects of habitat structure on resource availability, diet and growth of benthivorous perch, perca-fluviatilis1993In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 67, no 3, p. 403-414Article in journal (Refereed)
    Abstract [en]

    I experimentally evaluated the impact of habitat structural complexity on the interactions between a generalist predator and a benthic macroinvertebrate prey assemblage in a freshwater pond. Benthivorous perch (Perca fluviatilis) were stocked over a range of natural densities (no fish, low, and high densities) into enclosures with or without dense submerged vegetation. The biomass of macroinvertebrate prey decreased over time in the presence of perch and was always higher in enclosures with vegetation present than in enclosures lacking vegetation. The increase in mass of perch was positively related to the abundance of macroinvertebrate prey and negatively related to perch density and the density of vegetation. In the treatments lacking vegetation, the proportion of zooplankton in the diet of perch increased, and the growth rate of perch decreased over time. In the vegetation treatments, the proportion of zooplankton in the diet was low throughout the experiment and the growth rate of perch was constant over time. As a consequence, initial increase in mass was considerably higher in the treatments lacking vegetation than in the vegetation treatments, whereas no such pattern was observed in the second half of the experiment. In the absence of vegetation, perch are apparently able to forage efficiently, but this may reduce the availability of macroinvertebrate prey to the extent that perch are forced to include less profitable zooplankton prey into their diet. In vegetated habitats, the foraging efficiency of perch is reduced, which possibly prevents over-exploitation of macroinvertebrate prey and consequently may allow for a moderate, but relatively constant, consumption of macroinvertebrates by perch. The density-dependence of growth rates in both vegetated and unvegetated habitats can only partly be explained by resource competition, which suggests the presence of an additional mechanism of density-dependence. In natural lake communities, efficient predation from benthivorous fish should keep the biomass of macroinvertebrate prey in structurally simple habitats below the high levels initially present in my experiment. In these communities, submerged vegetation may be an equally profitable habitat for juvenile perch as are open areas. Through its effects on the feeding efficiencies of juvenile perch and other benthivorous fish, submerged vegetation may affect individual growth rates and the size structure of perch populations, which may contribute to explain differences in fish community structure among lakes differing in submerged vegetation cover.

  • 287.
    Diehl, Sebastian
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Relative consumer sizes and the strengths of direct and indirect interactions in omnivorous feeding relationships1993In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 68, no 1, p. 151-157Article in journal (Refereed)
    Abstract [en]

    Omnivory (the consumption of resources from more than one trophic level) is widespread in nature and has the potential to produce a richness of indirect effects. Nevertheless, its effects on population dynamics have received very little attention. In its simplest case, omnivory involves a top consumer, an intermediate consumer, and a resource that is common to both consumers. Simple models predict that the intermediate consumer can only coexist with the top consumer if the former is more efficient in exploiting the common resource, which would imply a net positive effect of the top consumer on the equilibrium density of resources (compared to the situation where only the intermediate consumer is present). Among 22 experimental manipulations of omnivorous top consumers I found only 2 studies in which top consumers had significant positive effects on resources. This discrepancy between experimental results and model predictions is, at least partly, related to deviations of the experimental systems from model assumptions. However, considerations of relative body sizes of intermediate and top consumers suggest, that top consumers having negative net effects on the basic resource should be common in nature. I argue that in systems where intermediate consumers and basic resources are relatively similar in size, but both are much smaller than omnivorous top consumers (e.g. vertebrate omnivores feeding on benthos, soil invertebrates, terrestrial insects etc.), the direct negative effect of top consumers on basic resources should not be outweighed by indirect positive effects, and that other mechanisms (e.g. prey refuges) must be invoked to explain the persistence of intermediate consumers in many natural systems. I further argue that a better knowledge of the population dynamical consequences of omnivory and the role of relative consumer sizes is necessary to improve our understanding of the-trophic dynamics of different kinds of communities.

  • 288.
    Diehl, Sebastian
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Berger, Stella
    Uszko, Wojciech
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Stibor, Herwig
    Stoichiometric mismatch causes a warming-induced regime shift in experimental plankton communitiesManuscript (preprint) (Other academic)
  • 289.
    Diehl, Sebastian
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Lundberg, Peter A
    Gardfjell, Hans
    Oksanen, Lauri
    Persson, Lennart
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Daphnia-phytoplankton interactions in lakes: is there a need for ratio-dependent consumer-resource models?1993In: American Naturalist, ISSN 0003-0147, E-ISSN 1537-5323, Vol. 142, no 6, p. 1052-1061Article in journal (Refereed)
  • 290.
    Diehl, Sebastian
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Integrated Science Lab (IceLab), Umeå University, Sweden.
    Thomsson, Gustaf
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Kahlert, Maria
    Guo, Junwen
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Karlsson, Jan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Liess, Antonia
    Inverse relationship of epilithic algae and pelagic phosphorus in unproductive lakes: Roles of N-2 fixers and light2018In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 63, no 7, p. 662-675Article in journal (Refereed)
    Abstract [en]

    Phosphorus (P) often limits the biomass of primary producers in freshwater lakes. However, in unproductive northern lakes, where anthropogenic nitrogen (N) deposition is low, N instead of P can limit primary producers. In addition, light can be limiting to primary producers at high concentrations of coloured dissolved organic matter (cDOM), as cDOM is the major determinant of light penetration in these lakes.

    To address resource limitation of epilithic algal biomass, we repeatedly sampled epilithon (periphyton on stony substrata) in 20 lakes covering a large, correlated cDOM and N‐deposition gradient across boreal and subarctic Sweden. Across these lakes, pelagic total N (TN) and total P (TP) were positively correlated, and benthic light supply was negatively correlated, with cDOM. Microscopically determined algal biovolume and epilithic carbon (C), N and P were subsequently regressed against benthic light supply and pelagic TN and TP.

    Patterns in epilithic biovolume were driven by N2‐fixing cyanobacteria, which accounted for 2%–90% of total epilithic biovolume. Averaged over the growing season, epilithic algal biovolume, C and N were negatively related to TP and positively to TN, and were highest in the clearest, most phosphorus‐poor lakes, where epilithon was heavily dominated by potentially N2‐fixing cyanobacteria.

    A structural equation model supports the hypothesis that cDOM had two counteracting effects on total epilithic algal biovolume: a positive one by providing N to algae that depend on dissolved N for growth, and a negative one by shading N2‐fixing cyanobacteria, with the negative effect being somewhat stronger.

    Together, these findings suggest that (1) light and N are the main resources limiting epilithic algal biomass in boreal to subarctic Swedish lakes, (2) epilithic cyanobacteria are more competitive in high‐light and low‐nitrogen environments, where their N2‐fixing ability allows them to reach high biomass, and (3) epilithic N increases with N2 fixer biomass and is—seemingly paradoxically—highest in the most oligotrophic lakes.

  • 291.
    Diehl, Sebastian
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Thomsson, Gustaf
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Wickman, Jonas
    Umeå University, Faculty of Science and Technology, Department of Mathematics and Mathematical Statistics.
    Vasconcelos, Francisco R.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Uszko, Wojciech
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Ask, Jenny
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Karlsson, Jan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Byström, Pär
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Resource and consumer control of cross-habitat trophic interactions in shallow lakesManuscript (preprint) (Other academic)
  • 292.
    Dietrich, Anna L.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Use of phytometers for evaluating ecological restoration2013Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The increase in ecological restoration can be attributed to valuation of healthyecosystems and concerns for future climate changes. Freshwaters belong among theglobally most altered ecosystems and are restored to counteract human impacts.Many Swedish streams that were channelized to facilitate timber floating have beenrestored by returning boulders and reconnecting riparian with instream habitats.Evaluation of restoration lacks reliable indicators of organism performance, possiblydue to the complexity of ecosystem responses. Phytometers, i.e. standardized plantstransplanted to different environments, are important indicators of restorationsuccess. Phytometers integrate multiple environmental factors and measureecosystem functions directly. This thesis combines a literature review with threeexperiments and focuses on phytometer use for evaluating ecological restoration. Werecommend using different phytometer species, life-forms and life-stages and longexperiments (>1 year) to obtain high resolution and generality (I). In greenhouse andfield experiments we investigated the effect of restoring channelized rivers onphytometers and abiotic variables in the riparian zone. We hypothesized thatphytometer performance varies with stream size and climate. In the greenhouse, weanalysed differences in fertility between channelized and restored reaches by growingphytometers on soils from experimental sites (II). Phytometers grew better on soilsfrom restored sites in small streams, indicating a positive effect of restoration on soil.We detected this effect already 3-7 years after restoration, suggesting a fasterrecovery than predicted. In a short-term field experiment focusing on germinationand establishment of sunflowers, seedling survival, substrate availability, and soilnutrient content in large streams were enhanced by restoration (III). Overall,phytometers performed best at high altitudes and short growing seasons. The use ofMolinia caerulea and Filipendula ulmaria as phytometers in a long-term fieldexperiment (IV) revealed a better performance at restored sites. One reason was thatsummer flow-variability was higher, particularly in medium-sized streams. Sincephytometers allocated more biomass to belowground parts at restored compared tochannelized sites, it seems important to separate above- and belowground biomass inrestoration evaluation. Restoration outcomes vary with location in the catchment.Knowing such potentially different responses could guide restorationists in where tolocate restoration to be effective or successful. We suggest that small streams reactparticularly fast to restoration. Given that the proportion of small streams is high andthat restoration success in headwaters may favour downstream reaches, werecommend restoration to begin in tributaries to larger rivers. It is not always knownwhy phytometers react the way they do. Greenhouse experiments can disentangle thecauses of phytometer responses in the field by focusing on single environmentalfactors. We demonstrate that phytometers integrate ecosystem responses torestoration by reflecting how environmental factors affect plants under fieldconditions. Further studies are needed to better understand the underlyingmechanisms.

  • 293.
    Dietrich, Anna L.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jansson, Roland
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    A phytometer study evaluating the effects of stream restoration on riparian vegetation2016In: Ecohydrology, ISSN 1936-0584, E-ISSN 1936-0592, Vol. 9, no 4, p. 646-658Article in journal (Refereed)
    Abstract [en]

    Channelization of streams and rivers to facilitate timber floating has cut off riparian zones from the channel, covered them with coarse sediment and resulted in less flooding. Restoration measures aiming to counteract these impacts are expected to create a higher, more natural hydrological variability and enhance site quality for riparian plants. In a long-term field experiment, we evaluated the effect of flooding regime on riparian plant performance by measuring survival and biomass increment of two transplanted phytometer species, a grass (Molinia caerulea) and a forb (Filipendula ulmaria). We also analysed the number and duration of flooding events in channelized and restored stream and river reaches with an indirect method using diurnal temperature oscillation. We found that flow duration was higher, with significantly more flood events at restored compared with channelized sites in medium-sized and large watercourses, particularly during the summer months. Phytometer performance was better at restored sites, and it was positively correlated with duration and frequency of summer flooding, indicating that more but less intense floods after restoration improved site conditions for phytometer growth. This may not only result from an increased heterogeneity in channel morphology caused by the return of boulders but can probably also be attributed to a reduced current velocity at restored sites. Flood variables were more often correlated with other abiotic variables at restored than at channelized sites, which points to an increased land-water connectivity as a result of restoration. 

  • 294.
    Dietrich, Anna
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Lind, Lovisa
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jansson, Roland
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    The Use of Phytometers for Evaluating Restoration Effects on Riparian Soil Fertility2014In: Journal of Environmental Quality, ISSN 0047-2425, E-ISSN 1537-2537, Vol. 43, no 6, p. 1916-1925Article in journal (Refereed)
    Abstract [en]

    The ecological restoration of streams in Sweden has become increasingly important to counteract effects of past timber floating. In this study, we focused on the effect on riparian soil properties after returning coarse sediment (cobbles and boulders) to the channel and reconnecting riparian with instream habitats. Restoration increases habitat availability for riparian plants, but its effects on soil quality are unknown. We also analyzed whether the restoration effect differs with variation in climate and stream size. We used standardized plant species to measure the performance of a grass (Phleum pratense L.) and a forb (Centaurea cyanus L.) in soils sampled in the riparian zones of channelized and restored streams and rivers. Furthermore, we analyzed the mass fractions of carbon (C) and nitrogen (N) along with the proportions of the stable isotopes C-13 and N-15 in the soil, as well as its grain size composition. We found a positive effect of restoration on biomass of phytometers grown in riparian soils from small streams, indicating that restoration enhanced the soil properties favoring plant performance. We suggest that changed flooding with more frequent but less severe floods and slower flows, enhancing retention, could explain the observed patterns. This positive effect suggests that it may be advantageous to initiate restoration efforts in small streams, which make up the highest proportion of the stream network in a catchment. Restoration responses in headwater streams may then be transmitted downstream to facilitate recovery of restored larger rivers. If the larger rivers were restored first, a slower reaction would be expected.

  • 295.
    Dietrich, Anna
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jansson, Roland
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    A long-term phytometer study to evaluate stream restoration along climate and discharge gradientsManuscript (preprint) (Other academic)
    Abstract [en]

    Simplified channel morphology caused by the channelization of rivers to facilitatetimber floating resulted in a less variable flow regime with faster flows in the mainchannel. Restoration measures aiming to counteract these impacts, such as the returnof boulders to the channel and the reconnection of the riparian zone with instreamhabitats, are expected to create a higher, more natural hydrological variability andenhance riparian site quality. In this study, we analysed the number and duration offlooding events at channelized and restored river reaches with an indirect methodusing diurnal temperature oscillation. In a long-term field experiment, we evaluatedthe effect of flooding regime on riparian plant performance by measuring survival andbiomass increment of two transplanted phytometer species, a grass (Molinia caerulea)and a forb (Filipendula ulmaria). We found that flow variability was significantlyhigher at restored compared to channelized sites in medium-sized and large streams,particularly during summer months. Phytometer performance was better at restoredsites and positively correlated with summer flooding, indicating that a more variableflow after restoration improved site conditions for phytometer growth. This may notonly result from the higher heterogeneity in channel morphology caused by thereturned boulders, but can probably also be attributed to a lower flow velocity atrestored sites. Flood variables were more often correlated with other abiotic variablesat restored than at channelized sites, which points to an increased land-waterconnectivity as a result of restoration.

  • 296.
    Dietrich, Anna
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jansson, Roland
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Phytometers are underutilised for evaluating ecological restoration2013In: Basic and Applied Ecology, ISSN 1439-1791, E-ISSN 1618-0089, Vol. 14, no 5, p. 369-377Article in journal (Refereed)
    Abstract [en]

    Ecological restoration increases, but evaluation of restoration efforts is inadequate because reliable performance indicators are lacking. As plants are important actors in ecological restoration, we suggest that they be used as meters, i.e. phytometers, of restoration success. Phytometer plants are transplanted to different conditions to integrate measures of the prevailing conditions. We analysed 100 studies for the use of phytometers and especially their applicability to evaluate ecological restoration. Most studies employed single species and life-stages and focused on habitat conditions and environmental impacts. Most experiments were conducted on grasslands in wet temperate regions. Growth was the dominant response variable, in long-term studies often combined with reproductive output and plant survival. Only five studies specifically evaluated ecological restoration, implying that its potential is not yet realised. We found phytometers promising in evaluating restoration outcomes given that they are easy to measure, can provide rapid results, and serve as integrative indicators of environmental conditions with the ability of covering many aspects of plant life and ecosystem processes. To evaluate restoration success with high resolution and generality, we suggest a combination of different phytometer species, life-forms and life-stages, and experimental periods >1 year to reduce effects of transplantation and between-year variation and to account for time lags in ecological processes and changes after restoration.

  • 297. Dinasquet, J.
    et al.
    Titelman, J.
    Moller, L. F.
    Setala, O.
    Granhag, L.
    Andersen, T.
    Båmstedt, Ulf
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Haraldsson, M.
    Hosia, A.
    Katajisto, T.
    Kragh, T.
    Kuparinen, J.
    Schroter, M. -L
    Sondergaard, M.
    Tiselius, P.
    Riemann, L.
    Cascading effects of the ctenophore Mnemiopsis leidyi on the planktonic food web in a nutrient-limited estuarine system2012In: Marine Ecology Progress Series, ISSN 0171-8630, E-ISSN 1616-1599, Vol. 460, p. 49-61Article in journal (Refereed)
    Abstract [en]

    Increasing biomasses of gelatinous zooplankton presumably have major implications for the structure and function of marine food webs at large; however, current data on lower trophic levels are scarce, as most studies have focused on the immediate effects on zooplankton and fish larvae only. We examined the short-term impact of larvae and adults of the invasive ctenophore Mnemiopsis leidyi on a summer planktonic food web in the estuarine southern Baltic Sea, with special emphasis on the microbial loop. Grazing by M. leidyi reduced the mesozooplankton biomass, followed by increased dinoflagellate biomass in treatments with M. leidyi. While chlorophyll a increased most in the treatments with M. leidyi, small phytoplankton and ciliates decreased in all treatments. M. leidyi had a slight effect on bacterial abundance, but not on bacterial production, ectoenzymatic activities, or community composition. Undetectable levels of phosphate and a gradual accumulation of dissolved organic carbon during the experiment suggested a malfunctioning microbial loop scenario. The experiment shows that direct and indirect short-term effects of M. leidyi on the estuarine food web are limited to higher trophic levels and indicates that top-down and bottom-up consequences of M. leidyi expansions on the microbial loop will likely depend on local nutrient conditions.

  • 298.
    Doi, Hideyuki
    et al.
    Institute for Chemistry and Biology of the Marine Environment, Carl-von-Ossietzky University Oldenburg.
    Cherif, Mehdi
    Department of Biology, McGill University.
    Iwabuchi, Tsubasa
    Graduate School of Life Science, Tohoku University.
    Katano, Izumi
    Institute for Chemistry and Biology of the Marine Environment, Carl-von-Ossietzky University Oldenburg.
    Stegen, James C.
    Dept of Biology, University of North Carolina.
    Striebel, Maren
    WasserCluster Lunz, University for Natural Resources and Applied Life Sciences.
    Integrating elements and energy through the metabolic dependencies of gross growth efficiency and the threshold elemental ratio2010In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 119, no 5, p. 752-765Article in journal (Refereed)
    Abstract [en]

    Metabolic theory proposes that individual growth is governed through the mass- and temperature-dependence of metabolism, and ecological stoichiometry posits that growth is maximized at consumer-specific optima of resource elemental composition. A given consumer's optimum, the threshold elemental ratio (TER), is proportional to the ratio of its maximum elemental gross growth efficiencies (GGEs). GGE is defined by the ratio of metabolism-dependent processes such that GGEs should be independent of body mass and temperature. Understanding the metabolic-dependencies of GGEs and TERs may open the path towards a theoretical framework integrating the flow of energy and chemical elements through ecosystems. However, the mass and temperature scaling of GGEs and TERs have not been broadly evaluated. Here, we use data from 95 published studies to evaluate these metabolic-dependencies for C, N and P from unicells to vertebrates. We show that maximum GGEs commonly decline as power functions of asymptotic body mass and exponential functions of temperature. The rates of change in maximum GGEs with mass and temperature are relatively slow, however, suggesting that metabolism may not causally influence maximum GGEs. We additionally derived the theoretical expectation that the TER for C:P should not vary with body mass and this was supported empirically. A strong linear relationship between carbon and nitrogen GGEs further suggests that variation in the TER for C:N should be due to variation in consumer C:N. In general we show that GGEs may scale with metabolic rate, but it is unclear if there is a causal link between metabolism and GGEs. Further integrating stoichiometry and metabolism will provide better understanding of the processes governing the flow of energy and elements from organisms to ecosystems.

  • 299. Donati, Giuseppe
    et al.
    Balestri, Michela
    Phelps, Megan
    Mauguiere, Julie
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Campera, Marco
    Lemur Abundance in the Lowland Rainforest of Tsitongambarika, Southeastern Madagascar: Altitudinal and Latitudinal Comparisons2017In: Folia primatologica, ISSN 0015-5713, E-ISSN 1421-9980, Vol. 88, no 2, p. 109-110Article in journal (Other academic)
  • 300.
    Dressel, Sabrina
    et al.
    Sveriges lantbruksuniversitet .
    Sandström, Camilla
    Umeå University, Faculty of Social Sciences, Department of Political Science.
    Ericsson, Göran
    Sveriges lantbruksuniversitet .
    A meta-analysis of studies on attitudes toward bears and wolves across Europe 1976–20122015In: Conservation Biology, ISSN 0888-8892, E-ISSN 1523-1739, Vol. 29, no 2, p. 565-574Article in journal (Refereed)
    Abstract [en]

    The ranges of wolves (Canis lupus) and bears (Ursus arctos) across Europe have expanded recently, and it is important to assess public attitudes toward this expansion because responses toward these species vary widely. General attitudes toward an object are good predictors of broad behavioral patterns; thus, attitudes toward wolves and bears can be used as indicators to assess the social foundation for future conservation efforts. However, most attitude surveys toward bears and wolves are limited in scope, both temporally and spatially, and provide only a snapshot of attitudes. To extend the results of individual surveys over a much larger temporal and geographical range so as to identify transnational patterns and changes in attitudes toward bears and wolves over time, we conducted a meta-analysis. Our analysis included 105 quantitative surveys conducted in 24 countries from 1976 to 2012. Across Europe, people's attitudes were more positive toward bears than wolves. Attitudes toward bears became more positive over time, but attitudes toward wolves seemed to become less favorable the longer people coexisted with them. Younger and more educated people had more positive attitudes toward wolves and bears than people who had experienced damage from these species, and farmers and hunters had less positive attitudes toward wolves than the general public. For bears attitudes among social groups did not differ. To inform conservation of large carnivores, we recommend that standardized longitudinal surveys be established to monitor changes in attitudes over time relative to carnivore population development. Our results emphasize the need for interdisciplinary research in this field and more advanced explanatory models capable of capturing individual and societal responses to changes in large carnivore policy and management.

3456789 251 - 300 of 1290
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf