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  • 1.
    Bonnot, N. C.
    et al.
    Grimsö Wildlife Research Station, Department of Ecology, Swedish University of Agricultural Sciences, Riddarhyttan, 730 91, Sweden.
    Bergvall, U. A.
    Grimsö Wildlife Research Station, Department of Ecology, Swedish University of Agricultural Sciences, Riddarhyttan, 730 91, Sweden.
    Jarnemo, Anders
    Halmstad University, School of Business, Engineering and Science, The Rydberg Laboratory for Applied Sciences (RLAS).
    Kjellander, P.
    Grimsö Wildlife Research Station, Department of Ecology, Swedish University of Agricultural Sciences, Riddarhyttan, 730 91, Sweden.
    Who’s afraid of the big bad wolf?: Variation in the stress response among personalities and populations in a large wild herbivore2018In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 188, no 1, p. 85-95Article in journal (Refereed)
    Abstract [en]

    Faced with rapid environmental changes, individuals may express different magnitude and plasticity in their response to a given stressor. However, little is known about the causes of variation in phenotypic plasticity of the stress response in wild populations. In the present study, we repeatedly captured individual roe deer (Capreolus capreolus) from two wild populations in Sweden exposed to differing levels of predation pressure and measured plasma concentrations of stress-induced cortisol and behavioral docility. While controlling for the marked effects of habituation, we found clear between-population differences in the stress-induced cortisol response. Roe deer living in the area that was recently recolonized by lynx (Lynx lynx) and wolves (Canis lupus) expressed cortisol levels that were around 30% higher than roe deer in the human-dominated landscape free of large carnivores. In addition, for the first time to our knowledge, we investigated the stress-induced cortisol response in free-ranging newborn fawns and found no evidence for hypo-responsiveness during early life in this species. Indeed, stress-induced cortisol levels were of similar magnitude and differed between populations to a similar extent in both neonates and adults. Finally, at an individual level, we found that both cortisol and docility levels were strongly repeatable, and weakly negatively inter-correlated, suggesting that individuals differed consistently in how they respond to a stressor, and supporting the existence of a stress-management syndrome in roe deer. © 2018, The Author(s).

  • 2.
    Brönmark, Christer
    et al.
    Limnology, Department of Ecology, Lund University, Lund, Sweden.
    Weisner, Stefan E.B.
    Limnology, Department of Ecology, Lund University, Lund, Sweden.
    Decoupling of cascading trophic interactions in a freshwater, benthic food chain1996In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 108, no 3, p. 534-541Article in journal (Refereed)
    Abstract [en]

    Food chain theory provides explicit predictions for equilibrium biomasses among trophic levels in food chains of different lengths. Empirical studies on freshwater benthic food chains have typically been performed on chains with up to three levels and in field experiments with limited spatial and temporal scale. Here we use a ‘’natural snapshot experiment” approach to study equilibrium biomass and abundance among trophic levels in natural ponds differing only with respect to fish assemblage structure. Forty-four ponds were surveyed for their density and biomass of fish, snails and periphyton. Ponds were divided into three categories based on fish assemblage: ponds with no fish (two trophic levels), ponds with molluscivorous fish (three trophic levels), ponds with molluscivorous fish (three trophic levels) and ponds that also had piscivorous fish (four trophic levels). Ponds without fish had a high density and biomass of snails and a low biomass of periphyton, whereas snails with molluscivorous fish. In the presence of piscivores, molluscivore populations consisted of low numbers of large individuals. Snail assemblages in piscivore ponds were characterised by relatively high densities of small-bodied detritivorous species and periphyton biomass was not significantly different from ponds with three trophic levels. Thus, predictions from classic food chain theory were upheld in ponds with up to three trophic levels. In ponds with four trophic levels, however, there was a decoupling of the trophic cascade at the piscivore-molluscivore level. Gape-limited piscivory, predation on snails by molluscivores that have reached an absolute size refuge from predation, and changes in food preferences of the dominant snails are suggested to explain the observed patterns.

  • 3.
    Vretare Strand, Viveka
    et al.
    Limnology, Department of Ecology, Lund University, Sweden.
    Weisner, Stefan E.B.
    Halmstad University, School of Business and Engineering (SET), Biological and Environmental Systems (BLESS), Wetland Research Centre.
    Interactive effects of pressurized ventilation, water depth and substrate conditions on Phragmites australis2002In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 131, no 4, p. 490-497Article in journal (Refereed)
    Abstract [en]

    Pressurized ventilation acts to increase the oxygen supply to roots and rhizomes in some species of emergent plants. In a greenhouse experiment, we investigated how pressurized ventilation affected growth, biomass allocation and mineral content of Phragmites australis in two water depths (15 cm or 75 cm) and two substrates (organic sediment or sand). Through perforating each stem above the water surface, pressurized ventilation was inhibited without affecting oxygen diffusion. In controls, 10-20% of the stems were perforated to make certain that lack of efflux sites would not limit pressurized ventilation. Plants with inhibited pressurized ventilation had lower oxygen concentrations in their stem bases than control plants. Growth was lower in plants with inhibited pressurized ventilation compared to controls except when plants grew in a combination of sand and shallow water. In plants grown in an organic sediment, but not in those grown in sand, inhibition of pressurized ventilation resulted in decreased biomass allocation to soil roots but increased allocation to aquatic roots. Stem perforation affected the tissue concentrations of nitrogen, phosphorus, magnesium, manganese and aluminium but not of calcium or iron. We suggest that the lower growth in plants with inhibited pressurized ventilation was caused by decreased mineral uptake, which may have resulted from the decreased proportional allocation to soil root weight, from decreased mineral availability or from impaired root function. In plants grown in sand in shallow water, diffusion seemed to cover the oxygen demand, as pressurized ventilation did not affect growth.

  • 4.
    Weisner, Stefan E.B.
    Limnology, Department of Ecology, Lund University, Lund, Sweden.
    Long-term competitive displacement of Typha latifolia by Typha angustifolia in a eutrophic lake1993In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 94, no 3, p. 451-456Article in journal (Refereed)
    Abstract [en]

    This study follows the outcome of long-term competition between a broad-leaved and a narrow-leaved Typha species, T. latifolia and T. angustifolia respectively, in a eutrophic lake. The lake was bordered by a zone of T. latifolia, at one location interrupted by a T. angustifolia stand. Distributional changes of the T. angustifolia stand and the adjacent zone of T. latifolia were measured on aerial photographs (less-than-or-equal-to 13 years) and along ground-level transects (6 years). A second stand of T. angustifolia was established with transplanted ramets within a formerly homogeneous zone of T. latifolia, and displacement between the two species was measured along ground-level transects after 6 years. Differences between the species in shoot performance were investigated to help explain the relative competitive abilities of the two Typha species. T. angustifolia expanded at the expense of T. latifolia at all water depths where both species occurred, except in very shallow water. Expansion rates suggest that T. angustifolia was not affected by the presence of T. latifolia in water depths exceeding 0.25 m. The Typha species were significantly negatively associated according to rank correlations of shoot densities, and changes of shoot densities, along the transects. These results suggest that T. angustifolia is competitively superior to T. latifolia, contradicting earlier studies. The higher competitive ability of T. angustifolia is consistent with its having taller shoots and a higher standing crop in early summer. Further, shoot height distributions indicated a closer integration of shoot emergence during spring in T. angustifolia than in T. latifolia. A high leaf area/shoot weight ratio suggest that T. latifolia may instead be relatively fast-growing, achieving competitive superiority over narrower-leaved Typha species during a transient period after simultaneous seedling establishment.

  • 5.
    Weisner, Stefan E.B.
    et al.
    Limnology, Lund University, Lund, Sweden .
    Strand, John A.
    Limnology, Lund University, Lund, Sweden .
    Sandsten, Håkan
    Limnology, Lund University, Lund, Sweden .
    Mechanisms regulating abundance of submerged vegetation in shallow eutrophic lakes1997In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 109, no 4, p. 592-599Article in journal (Refereed)
    Abstract [en]

    Shallow eutrophic lakes tend to be either in a turbid state dominated by phytoplankton or in a clear-water state dominated by submerged macrovegetation. Recent studies suggest that the low water turbidity in the clear-water state is maintained through direct and in-direct effects of the submerged vegetation. This study examined what mechanisms may cause a recession of the submerged vegetation in the clear-water state, and thereby a switch to the turbid state. The spatial distribution of submerged vegetation biomass was investigated in two shallow eutrophic lakes in the clear-water state in southern Sweden. Biomass of submerged vegetation was positively correlated with water depth and wave exposure, which also were mutually correlated, suggesting that mechanisms hampering submerged vegetation were strongest at shallow and/or sheltered locations. The growth of Myriophyllum spicatum, planted in the same substrate and at the same water depth, was compared between sheltered and wave exposed sites in two lakes. After 6 weeks the plants were significantly smaller at the sheltered sites, where periphyton production was about 5 times higher than at the exposed sites. Exclosure experiments were conducted to evaluate the effects of waterfowl grazing on macrophyte biomass. Potamogeton pectinatus growth was decreased by grazing, whereas M. spicatum was not affected. The effects were greater at a sheltered than at a wave-exposed site, and also negatively related to distance from the reed belt. These results suggest that competition from epiphytes and waterfowl grazing hamper the development of submerged vegetation at sheltered and/or shallow locations. An increased strength of these mechanisms may cause a recession of submerged vegetation in shallow eutrophic lakes in the clear-water state and thereby a switch to the turbid state.

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