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  • 1. Aerts, R.
    et al.
    Callaghan, T. V.
    Dorrepaal, E.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Systems Ecology, Department of Ecological Science, VU University Amsterdam, Amsterdam, The Netherlands.
    van Logtestijn, R. S. P.
    Cornelissen, J. H. C.
    Seasonal climate manipulations have only minor effects on litter decomposition rates and N dynamics but strong effects on litter P dynamics of sub-arctic bog species2012Ingår i: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 170, nr 3, s. 809-819Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Litter decomposition and nutrient mineralization in high-latitude peatlands are constrained by low temperatures. So far, little is known about the effects of seasonal components of climate change (higher spring and summer temperatures, more snow which leads to higher winter soil temperatures) on these processes. In a 4-year field experiment, we manipulated these seasonal components in a sub-arctic bog and studied the effects on the decomposition and N and P dynamics of leaf litter of Calamagrostis lapponica, Betula nana, and Rubus chamaemorus, incubated both in a common ambient environment and in the treatment plots. Mass loss in the controls increased in the order Calamagrostis < Betula < Rubus. After 4 years, overall mass loss in the climate-treatment plots was 10 % higher compared to the ambient incubation environment. Litter chemistry showed within each incubation environment only a few and species-specific responses. Compared to the interspecific differences, they resulted in only moderate climate treatment effects on mass loss and these differed among seasons and species. Neither N nor P mineralization in the litter were affected by the incubation environment. Remarkably, for all species, no net N mineralization had occurred in any of the treatments during 4 years. Species differed in P-release patterns, and summer warming strongly stimulated P release for all species. Thus, moderate changes in summer temperatures and/or winter snow addition have limited effects on litter decomposition rates and N dynamics, but summer warming does stimulate litter P release. As a result, N-limitation of plant growth in this sub-arctic bog may be sustained or even further promoted.

  • 2.
    Albrectsen, Benedicte Riber
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysiologisk botanik. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Umeå Plant Science Centre (UPSC).
    Siddique, Abu Bakar
    Decker, Vicki Huizu Guo
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Umeå Plant Science Centre (UPSC). Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysiologisk botanik.
    Unterseher, Martin
    Robinson, Kathryn M
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysiologisk botanik. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Umeå Plant Science Centre (UPSC).
    Both plant genotype and herbivory shape aspen endophyte communities2018Ingår i: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 187, nr 2, s. 535-545Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Salicinoid phenolic glycosides are common defence substances in salicaceous trees and specialist leaf beetles use these compounds for their own defence against predators. Salicinoids vary qualitatively and qualitatively in aspen (Populus tremula) and this variation has a genetic basis. The foliar endophyte mycobiome is plentiful and we hypothesised that it is related to plant genotype, potentially mediated by salicinoid composition, and that interactions with the leaf beetle Chrysomela tremula may alter this relationship. We studied these three-way interactions in controlled greenhouse experiments. Endophytic fungi were isolated from sterilised leaf tissues with and without beetle damage, and from beetles. We confirmed that endophyte composition was influenced by host genotype. Beetle activity added generalist morphs to the mycobiome that overrode the initial host association. Yeast-like genera (Cryptococcus and Rhodotorula) were isolated only from beetle-damaged tissues and from beetles, whereas fast-growing filamentous fungi dominated beetle-free control plants. Competition experiments between filamentous fungi of plant origin and beetle-related yeasts suggested interaction of both stimulating and inhibiting modes of action amongst the fungi. As a result, we detected examples of amensalism, commensalism, parasitism and competition between the morphs tested, but we found no evidence of mutualism, and consequently no co-evolutionary relationship could be demonstrated, between yeasts carried by beetles, host genotype and associated filamentous morphs. Endophyte studies are method-dependent and high-throughput sequencing technology best define the fungal mycobiome, culturing however continues to be a cheap way to provide fundamental ecological insights and it is also required for experimental studies.

  • 3. Bartels, Pia
    et al.
    Cucherousset, Julien
    Gudasz, Cristian
    Jansson, Mats
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Karlsson, Jan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Persson, Lennart
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Premke, Katrin
    Rubach, Anja
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Steger, Kristin
    Tranvik, Lars J.
    Eklov, Peter
    Terrestrial subsidies to lake food webs: an experimental approach2012Ingår i: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 168, nr 3, s. 807-818Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Cross-ecosystem movements of material and energy are ubiquitous. Aquatic ecosystems typically receive material that also includes organic matter from the surrounding catchment. Terrestrial-derived (allochthonous) organic matter can enter aquatic ecosystems in dissolved or particulate form. Several studies have highlighted the importance of dissolved organic carbon to aquatic consumers, but less is known about allochthonous particulate organic carbon (POC). Similarly, most studies showing the effects of allochthonous organic carbon (OC) on aquatic consumers have investigated pelagic habitats; the effects of allochthonous OC on benthic communities are less well studied. Allochthonous inputs might further decrease primary production through light reduction, thereby potentially affecting autotrophic resource availability to consumers. Here, an enclosure experiment was carried out to test the importance of POC input and light availability on the resource use in a benthic food web of a clear-water lake. Corn starch (a C-4 plant) was used as a POC source due to its insoluble nature and its distinct carbon stable isotope value (delta C-13). The starch carbon was closely dispersed over the bottom of the enclosures to study the fate of a POC source exclusively available to sediment biota. The addition of starch carbon resulted in a clear shift in the isotopic signature of surface-dwelling herbivorous and predatory invertebrates. Although the starch carbon was added solely to the sediment surface, the carbon originating from the starch reached zooplankton. We suggest that allochthonous POC can subsidize benthic food webs directly and can be further transferred to pelagic systems, thereby highlighting the importance of benthic pathways for pelagic habitats.

  • 4.
    Deininger, Anne
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Faithfull, Carolyn
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Bergström, Ann-Kristin
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Nitrogen effects on the pelagic food web are modified by dissolved organic carbon2017Ingår i: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 184, nr 4, s. 901-916Artikel i tidskrift (Refereegranskat)
    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.

  • 5.
    Faithfull, Carolyn L.
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Mathisen, Peter
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Wenzel, Anja
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Bergström, Ann-Kristin
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Vrede, T.
    Food web efficiency differs between humic and clear water lake communities in response to nutrients and light2015Ingår i: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 177, nr 3, s. 823-835Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This study demonstrates that clear and humic freshwater pelagic communities respond differently to the same environmental stressors, i.e. nutrient and light availability. Thus, effects on humic communities cannot be generalized from existing knowledge about these environmental stressors on clear water communities. Small humic lakes are the most numerous type of lake in the boreal zone, but little is known about how these lakes will respond to increased inflows of nutrients and terrestrial dissolved organic C (t-DOC) due to climate change and increased human impacts. Therefore, we compared the effects of nutrient addition and light availability on pelagic humic and clear water lake communities in a mesocosm experiment. When nutrients were added, phytoplankton production (PPr) increased in both communities, but pelagic energy mobilization (PEM) and bacterial production (BP) only increased in the humic community. At low light conditions, the addition of nutrients led to increased PPr only in the humic community, suggesting that, in contrast to the clear water community, humic phytoplankton were already adapted to lower ambient light levels. Low light significantly reduced PPr and PEM in the clear water community, but without reducing total zooplankton production, which resulted in a doubling of food web efficiency (FWE = total zooplankton production/PEM). However, total zooplankton production was not correlated with PEM, PPr, BP, PPr:BP or C:nutrient stoichiometry for either community type. Therefore, other factors such as food chain length, food quality, ultra-violet radiation or duration of the experiment, must have determined total zooplankton production and ultimately FWE.

  • 6.
    Graae, Bente J.
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Ejrnaes, Rasmus
    Lang, Simone I.
    Meineri, Eric
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Ibarra, Pablo T.
    Bruun, Hans Henrik
    Strong microsite control of seedling recruitment in tundra2011Ingår i: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 166, nr 2, s. 565-576Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The inclusion of environmental variation in studies of recruitment is a prerequisite for realistic predictions of the responses of vegetation to a changing environment. We investigated how seedling recruitment is affected by seed availability and microsite quality along a steep environmental gradient in dry tundra. A survey of natural seed rain and seedling density in vegetation was combined with observations of the establishment of 14 species after sowing into intact or disturbed vegetation. Although seed rain density was closely correlated with natural seedling establishment, the experimental seed addition showed that the microsite environment was even more important. For all species, seedling emergence peaked at the productive end of the gradient, irrespective of the adult niches realized. Disturbance promoted recruitment at all positions along the environmental gradient, not just at high productivity. Early seedling emergence constituted the main temporal bottleneck in recruitment for all species. Surprisingly, winter mortality was highest at what appeared to be the most benign end of the gradient. The results highlight that seedling recruitment patterns are largely determined by the earliest stages in seedling emergence, which again are closely linked to microsite quality. A fuller understanding of microsite effects on recruitment with implications for plant community assembly and vegetation change is provided.

  • 7. Granath, Gustaf
    et al.
    Wiedermann, Magdalena M
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Strengbom, Joachim
    Physiological responses to nitrogen and sulphur addition and raised temperature in Sphagnum balticum2009Ingår i: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 161, nr 3, s. 481-490Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Sphagnum, the main genus which forms boreal peat, is strongly affected by N and S deposition and raised temperature, but the physiological mechanisms behind the responses are largely unknown. We measured maximum photosynthetic rate (NP(max)), maximum efficiency of photosystem II [variable fluorescence (F (v))/maximum fluorescence yield (F (m))] and concentrations of N, C, chlorophyll and carotenoids as responses to N and S addition and increased temperature in Sphagnum balticum (a widespread species in the northern peatlands) in a 12-year factorial experiment. NP(max) did not differ between control (0.2 g N m(-2) year(-1)) and high N (3.0 g N m(-2) year(-1)), but was higher in the mid N treatment (1.5 g N m(-2) year(-1)). N, C, carotenoids and chlorophyll concentration increased in shoot apices after N addition. F (v)/F (m) did not differ between N treatments. Increased temperature (+3.6A degrees C) had a small negative effect on N concentration, but had no significant effect on NP(max) or F (v)/F (m). Addition of 2 g S m(-2) year(-1) showed a weak negative effect on NP(max) and F (v)/F (m). Our results suggest a unimodal response of NP(max) to N addition and tissue N concentration in S. balticum, with an optimum N concentration for photosynthetic rate of similar to 13 mg N g(-1). In conclusion, high S deposition may reduce photosynthetic capacity in Sphagnum, but the negative effects may be relaxed under high N availability. We suggest that previously reported negative effects on Sphagnum productivity under high N deposition are not related to negative effects on the photosynthetic apparatus, but differences in optimum N concentration among Sphagnum species may affect their competitive ability under different N deposition regimes.

  • 8.
    Hambäck, Peter A
    et al.
    Department of Ecology and Environmental Science, Umeå University, Umeå, Sweden.
    Stenberg, Johan A
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi, miljö och geovetenskap.
    Ericson, Lars
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi, miljö och geovetenskap.
    Asymmetric indirect interactions mediated by a shared parasitoid: connecting species traits and local distribution patterns for two chrysomelid beetles2006Ingår i: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 148, nr 3, s. 475-481Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper reports on an asymmetric indirect interaction between two chrysomelid beetles where one species (Galerucella tenella) experiences higher parasitization, and the other species (Galerucella calmariensis) lower parasitization, in mixed compared with monospecific populations. This pattern is likely to be a consequence of differences in life history characteristics, where the inferior species has a smaller body size, a lower fecundity and supports a lower parasitoid density than the superior species. This connection between life history characteristics and interspecific dominance in host–parasitoid systems corresponds to predictions from current community ecology theory, and provides a useful building-block in the development of a predictive theory of parasitoid effects on host coexistence.

  • 9.
    Hedström, Per
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Bystedt, David
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Karlsson, Jan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Bokma, Folmer
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Byström, Pär
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Brownification increases winter mortality in fish2017Ingår i: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 183, nr 2, s. 587-595Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In northernclimateswinter is a bottleneck for many organisms. Low light and resource availability constrain individual foraging rates,potentially leading tostarvation and increasedmortality.Increasinginput of humic substances to aquatic ecosystems causesbrownification of water and hence a further decreaseof light availability,which may lead tofurther decreased foraging ratesand starvation mortality during winter.To test this hypothesis, we measured the effectsof experimentally increased humicwaterinput on consumption and survival of young-of-the-year (YOY) three-spined stickleback (Gasterosteus aculeatus) over winterin largeoutdoor enclosures. Population densitieswereestimated in autumn andthefollowing springand food availabilityand consumptionwere monitoredoverwinter. As hypothesized,mortality washigher underhumic(76%)as compared to ambientconditions (64%).Also, body condition and ingested prey biomass werelower under humic conditionseven thoughresource availability wasnotlower under humic conditions. Light conditions were significantly poorer under humic conditions. This suggeststhat increased mortality and decreased body condition and ingested prey biomasswasnot due to decreased resource availability but due todecreasedsearch efficiencyin this visual feeding consumer. Increased future brownification of aquatic systems may therefore negatively affect both recruitment and densities of fish.

  • 10. Hotchkiss, Erin R
    et al.
    Hall, Robert O
    Linking calcification by exotic snails to stream inorganic carbon cycling.2010Ingår i: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 163, nr 1, s. 235-44Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Biotic calcification is rarely considered in freshwater C budgets, despite calculations suggesting that calcifying animals can alter inorganic C cycling. Most studies that have quantified biocalcification in aquatic ecosystems have not directly linked CO(2) fluxes from biocalcification with whole-ecosystem rates of inorganic C cycling. The freshwater snail, Melanoides tuberculata, has achieved a high abundance and 37.4 g biomass m(-2) after invading Kelly Warm Springs in Grand Teton National Park. This high biomass suggests that introduced populations of Melanoides may alter ecosystem processes. We measured Melanoides growth rates and biomass to calculate the production of biomass, shell mass, and CO(2). We compared Melanoides biomass and inorganic C production with ecosystem C pools and fluxes, as well as with published rates of CO(2) production by other calcifying organisms. Melanoides calcification in Kelly Warm Springs produced 12.1 mmol CO(2) m(-2) day(-1) during summer months. We measured high rates of gross primary productivity and respiration in Kelly Warm Springs (-378 and 533 mmol CO(2) m(-2) day(-1), respectively); CO(2) produced from biocalcification increased net CO(2) production in Kelly Warm Springs from 155 to 167 mmol CO(2) m(-2) day(-1). This rate of CO(2) production via biocalcification is within the published range of calcification by animals. But these CO(2) fluxes are small when compared to ecosystem C fluxes from stream metabolism. The influence of animals is relative to ecosystem processes, and should always be compared with ecosystem fluxes to quantify the importance of a specific animal in its environment.

  • 11.
    Huss, Magnus
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi, miljö och geovetenskap.
    Byström, Pär
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi, miljö och geovetenskap.
    Persson, Lennart
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi, miljö och geovetenskap.
    Resource heterogeneity, diet shifts and intra-cohort competition: effects on size divergence in YOY fish2008Ingår i: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 158, nr 2, s. 249-257Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Most organisms exhibit a substantial size variation among individuals due to individual differences in experienced biotic and abiotic environmental conditions and because individuals undergo growth and development during most of their life time. One important issue in this context is how size variation within cohorts may develop over time. Here we tested the hypothesis, in gape-limited animals such as fish, that size divergence among individuals within a cohort depends on the opportunity to undergo size-dependent diet shifts, by allowing initially larger individuals to make an early diet shift when the first resource becomes limiting. We used young-of-the-year perch (Perca fluviatilis) as our study organism. Competitive intensity and the opportunity to undergo a diet shift from zooplankton to macroinvertebrates affected both mean growth rates and the extent to which inter-individual variation in growth was manifested. As predicted, increased competition combined with the presence of both zooplankton and benthic macroinvertebrates increased the degree of size variation. However, size divergence was also observed among individuals when only the initial resource, zooplankton, was available. We argue that only non-exploitative interactions, such as dominance structures and social interactions could have caused this latter pattern, as exploitative competition is expected to lead to size convergence due to the superior competitive ability of smaller individuals. Our results suggest that diet shifts are not a prerequisite for size divergence in animal cohorts and that dominance and social interactions may have similar effects on size variation within cohorts. Finally, development of size variation is suggested to have strong implications for overall cohort performance.

  • 12.
    Huss, Magnus
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi, miljö och geovetenskap.
    Persson, Lennart
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi, miljö och geovetenskap.
    Byström, Pär
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi, miljö och geovetenskap.
    The origin and development of individual size variation in early pelagic stages of fish2007Ingår i: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 153, nr 1, s. 57-67Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Size variation among individuals born at the same time in a common environment (within cohorts) is a common phenomenon in natural populations. Still, the mechanisms behind the development of such variation and its consequences for population processes are far from clear. We experimentally investigated the development of early within-cohort size variation in larval perch (Perca fluviatilis). Specifically we tested the influence of initial variation, resulting from variation in egg strand size, and intraspecific density for the development of size variation. Variation in egg strand size translated into variation in initial larval size and time of hatching, which, in turn, had effects on growth and development. Perch from the smallest egg strands performed on average equally well independent of density, whereas larvae originating from larger egg strands performed less well under high densities. We related this difference in density dependence to size asymmetries in competitive abilities leading to higher growth rates of groups consisting of initially small individuals under high resource limitation. In contrast, within a single group of larvae, smaller individuals grew substantially slower under high densities whereas large individuals performed equally well independent of density. As a result, size variation among individuals within groups (i.e. originating from the same clutch) increased under high densities. This result may be explained by social interactions or differential timing of diet shifts and a depressed resource base for the initially smaller individuals. It is concluded that to fully appreciate the effects of density-dependent processes on individual size variation and size-dependent growth, consumer feedbacks on resources need to be considered.

  • 13.
    Högberg, Mona N.
    et al.
    Department of Forest Ecology, Swedish University of Agricultural Sciences, Umea.
    Myrold, David D.
    Department of Crop and Soil Science, Oregon State University, Corvallis, USA.
    Giesler, Reiner
    Department of Forest Ecology, Swedish University of Agricultural Sciences, Umeå.
    Högberg, Peter
    Department of Forest Ecology, Swedish University of Agricultural Sciences, Umeå.
    Contrasting patterns of soil N-cycling in model ecosystems of Fennoscandian boreal forests2006Ingår i: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 147, nr 1, s. 96-107Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The low plant productivity of boreal forests ingeneral has been attributed to low soil N supply and lowtemperatures. Exceptionally high productivity occurs intoe-slope positions, and has been ascribed to influx of Nfrom surrounding areas and higher rates of soil Nturnover in situ. Despite large apparent natural variationsin forest productivity, rates of gross soil N mineralizationand gross nitrification have never beencompared in Fennoscandian boreal forests of contrastingproductivity. We report contrasting patterns of soilN turnover in three model ecosystems, representing therange in soil C-to-N ratios (19–41) in Fennoscandianboreal forests and differences in forest productivity by afactor close to 3. Gross N mineralization was seventimes higher when soil, microbial, and plant C-to-Nratios were the lowest compared to the highest. Thisprocess, nitrification and potential denitrification correlatedwith inorganic, total and microbial biomass N, butnot microbial C. There was a constant ratio between soiland microbial C-to-N ratio of 3.7±0.2, across wide ratiosof soil C-to-N and fungi-to-bacteria. Soil N-cyclingshould be controlled by the supplies of C and N to themicrobes. In accordance with plant allocation theory, wediscuss the possibility that the high fungal biomass athigh soil C-to-N ratio reflects a particularly high supplyof plant photosynthates, substrates of high-quality C, tomycorrhizal fungi. Methods to study soil N turnoverand N retention should be developed to take into accountthe impact of mycorrhizal fungi on soil N-cycling.

  • 14.
    Jonsson, Anna
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi, miljö och geovetenskap.
    Moen, Jon
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi, miljö och geovetenskap.
    Palmqvist, Kristin
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi, miljö och geovetenskap.
    Predicting lichen hydration using biophysical models.2008Ingår i: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 156, nr 2, s. 259-73Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Two models for predicting the hydration status of lichens were developed as a first step towards a mechanistic lichen productivity model. A biophysical model included the water potential of the air, derived from measurements of air temperature, relative humidity and species-specific rate constants for desiccation and rehydration. A reduced physical model, included only the environmental parameters, assuming instantaneous equilibration between the lichen and the air. These models were developed using field and laboratory data for three green algal lichens; the foliose epiphytic Platismatia glauca (L.) W. Culb., the fruticose epiphytic Alectoria sarmentosa (Ach.) Ach., and the fruticose, terricolous and mat-forming Cladina rangiferina (L.) Weber ex Wigg. The models were compared and validated for the same three species using data from a habitat with a different microclimate. Both models predicted length and timing of lichen hydration periods with high accuracy for A. sarmentosa and P. glauca where near 100 percent of the total wet time was predicted by the biophysical and the physical model. Moreover, the models predicted an accurate timing of the total realized wet time for A. sarmentosa and P. glauca when the lichens were wet. The model accuracy was lower for C. rangiferina compared to the epiphytes, both for the total realized wet time and timing accuracy. The results demonstrate that the stochastic and continually varying hydration status of lichens can be simulated from biophysical data. Further development of these models to include also water related activity, light, and temperature conditions during the hydration events, will then be a potent tool to assess potential lichen productivity in landscapes and habitats of various microclimatic conditions.

  • 15.
    Jonsson, Micael
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi, miljö och geovetenskap.
    Malmqvist, Björn
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi, miljö och geovetenskap.
    Mechanisms behind positive diversity effects on ecosystem functioning: testing the facilitation and interference hypotheses2003Ingår i: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 134, nr 4, s. 554-559Artikel i tidskrift (Refereegranskat)
  • 16. Khalil, Hussein
    et al.
    Ecke, Frauke
    Evander, Magnus
    Umeå universitet, Medicinska fakulteten, Institutionen för klinisk mikrobiologi, Virologi.
    Hornfeldt, Birger
    Selective predation on hantavirus-infected voles by owls and confounding effects from landscape properties2016Ingår i: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 181, nr 2, s. 597-606Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    It has been suggested that predators may protect human health through reducing disease-host densities or selectively preying on infected individuals from the population. However, this has not been tested empirically. We hypothesized that Tengmalm's owl (Aegolius funereus) selectively preys on hantavirus-infected individuals of its staple prey, the bank vole (Myodes glareolus). Bank voles are hosts of Puumala hantavirus, which causes a form of hemorrhagic fever in humans. Selective predation by owls on infected voles may reduce human disease risk. We compared the prevalence of anti-Puumala hantavirus antibodies (seroprevalence), in bank voles cached by owls in nest boxes to seroprevalence in voles trapped in closed-canopy forest around each nest box. We found no general difference in seroprevalence. Forest landscape structure could partly account for the observed patterns in seroprevalence. Only in more connected forest patches was seroprevalence in bank voles cached in nest boxes higher than seroprevalence in trapped voles. This effect disappeared with increasing forest patch isolation, as seroprevalence in trapped voles increased with forest patch isolation, but did not in cached voles. Our results suggest a complex relationship between zoonotic disease prevalence in hosts, their predators, and landscape structure. Some mechanisms that may have caused the seroprevalence patterns in our results include higher bank vole density in isolated forest patches. This study offers future research potential to shed further light on the contribution of predators and landscape properties to human health.

  • 17. Kreyling, Juergen
    et al.
    Haei, Mahsa
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Laudon, Hjalmar
    Absence of snow cover reduces understory plant cover and alters plant community composition in boreal forests2012Ingår i: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 168, nr 2, s. 577-587Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Snow regimes affect biogeochemistry of boreal ecosystems and are altered by climate change. The effects on plant communities, however, are largely unexplored despite their influence on relevant processes. Here, the impact of snow cover on understory community composition and below-ground production in a boreal Picea abies forest was investigated using a long-term (8-year) snow cover manipulation experiment consisting of the treatments: snow removal, increased insulation (styrofoam pellets), and control. The snow removal treatment caused longer (118 vs. 57 days) and deeper soil frost (mean minimum temperature -5.5 vs. -2.2 degrees C) at 10 cm soil depth in comparison to control. Understory species composition was strongly altered by the snow cover manipulations; vegetation cover declined by more than 50% in the snow removal treatment. In particular, the dominant dwarf shrub Vaccinium myrtillus (-82%) and the most abundant mosses Pleurozium schreberi (-74%) and Dicranum scoparium (-60%) declined strongly. The C:N ratio in V. myrtillus leaves and plant available N in the soil indicated no altered nitrogen nutrition. Fine-root biomass in summer, however, was negatively affected by the reduced snow cover (-50%). Observed effects are attributed to direct frost damage of roots and/or shoots. Besides the obvious relevance of winter processes on plant ecology and distribution, we propose that shifts in the vegetation caused by frost damage may be an important driver of the reported alterations in biogeochemistry in response to altered snow cover. Understory plant performance clearly needs to be considered in the biogeochemistry of boreal systems in the face of climate change.

  • 18. Kreyling, Juergen
    et al.
    Haei, Mahsa
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Laudon, Hjalmar
    Erratum to: Absence of snow cover reduces understory plant cover and alters plant community composition in boreal forests (vol 168, pg 577, 2012)2013Ingår i: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 173, nr 3, s. 1157-1157Artikel i tidskrift (Refereegranskat)
  • 19. Lehndal, Lina
    et al.
    Hambäck, Peter A
    Ericson, Lars
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Ågren, Jon
    Herbivory strongly influences among-population variation in reproductive output of Lythrum salicaria in its native range2016Ingår i: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 180, nr 4, s. 1159-1171Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Herbivory can negatively affect several components of plant reproduction. Yet, because of a lack of experimental studies involving multiple populations, the extent to which differences in herbivory contribute to among-population variation in plant reproductive success is poorly known. We experimentally determined the effects of insect herbivory on reproductive output in nine natural populations of the perennial herb Lythrum salicaria along a disturbance gradient in an archipelago in northern Sweden, and we quantified among-population differentiation in resistance to herbivory in a common-garden experiment in the same area. The intensity of leaf herbivory varied > 500-fold and mean female reproductive success > 400-fold among the study populations. The intensity of herbivory was lowest in populations subject to strong disturbance from ice and wave action. Experimental removal of insect herbivores showed that the effect of herbivory on female reproductive success was correlated with the intensity of herbivory and that differences in insect herbivory could explain much of the among-population variation in the proportion of plants flowering and seed production. Population differentiation in resistance to herbivory was limited. The results demonstrate that the intensity of herbivory is a major determinant of flowering and seed output in L. salicaria, but that differences in herbivory are not associated with differences in plant resistance at the spatial scale examined. They further suggest that the physical disturbance regime may strongly influence the performance and abundance of perennial herbs and patterns of selection not only because of its effect on interspecific competition, but also because of effects on interactions with specialized herbivores.

  • 20.
    Liess, Antonia
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Lange, K
    The snail Potamopyrgus antipodarum grows faster and is more active in the shade, independent of food quality2011Ingår i: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 167, nr 1, s. 85-96Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Ecological stoichiometry has advanced food web ecology by emphasising the importance of food quality over food quantity for herbivores. Here, we focus on the effects of abiotic factors such as nutrients and light (known to influence food quality) on grazer growth rates. As model organism we used the mudsnail Potamopyrgus antipodarum that is native to New Zealand but invasive elsewhere. In a stream channel experiment in New Zealand, we manipulated light (two levels) and nutrients (four levels) to achieve a range of primary producer carbon: nutrient ratios and added mudsnails (3 densities + ungrazed control) to 128 periphyton covered stream channels in a 2 × 4 × 4 full factorial design. We measured snail growth rate and activity, food quality and nutritional imbalance, to test the predictions that (1) less light and more nutrients increase periphyton food quality and thus snail growth rates, and (2) less crowding leads to higher food availability and thus higher snail growth rates. We found that snail growth rates were higher under low light than under high light intensities and this difference increased with increasing nutrient addition. These changes in growth rate were not mediated by food quality in terms of periphyton nutrient ratios. Furthermore, experimental treatments strongly affected snail behaviour. Snails grazed more actively in the low light treatments, and thus it is more likely that snail growth rates were directly affected by light levels, maybe as a result of innate predator avoidance behaviour or as a reaction to high UV intensities. We conclude that in our stream channels snail growth rate was limited by factors other than food quality and quantity such as UV exposure, algal defences or the relatively low ambient water temperature.

  • 21. Mathews, Lauren
    et al.
    Faithfull, Carolyn L.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Center for Microbial Oceanography: Research and Education, Department of Oceanography and Sea Grant College Program, University of Hawai‘i at Mānoa, Honolulu, USA; Gävleborg County Administrative Board, Gävle, Sweden.
    Lenz, Petra H.
    Nelson, Craig E.
    The effects of food stoichiometry and temperature on copepods are mediated by ontogeny2018Ingår i: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 188, nr 1, s. 75-84Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Climate change is warming the oceans, increasing carbon dioxide partial pressure and reducing nutrient recycling from deep layers. This will affect carbon (C) and phosphorus (P) availability in the oceans, thus, altering the balance between the nutrient content of consumers and their food resource. The combined effects of food quality and temperature have been investigated for adult copepods; however, nauplii, the early developmental stages of copepods, often far outnumber adults, grow more rapidly and have a higher phosphorus body content and demand than later life stages. Consequently, ontogeny may affect how copepods respond to the combined stressors of increasing temperature and altered food stoichiometry. We conducted temperature-controlled experiments (24, 28 and 32 A degrees C) where Parvocalanus crassirostris was fed either a P-replete or a P-limited phytoplankton food source. Reduced survival of nauplii and copepodites at the highest temperature was ameliorated when fed P-replete food. At higher temperatures, copepodite growth remained stable, but internal C:P stoichiometry diverged in the direction of phytoplankton C:P, suggesting that increased temperature affected copepodite stoichiometric homeostasis. In contrast, naupliar P content increased with temperature and naupliar growth was P limited, suggesting nauplii required additional phosphorus at higher temperatures. We conclude that resource stoichiometry plays a key role in how copepod survival and growth are impacted by temperature, and that ontogeny mediates these responses. Our results suggest that as the extent of warming oceans and phytoplankton nutrient limitation increase, copepod survival and the growth of early life stages may decline.

  • 22.
    McKie, Brendan G
    et al.
    Department of Aquatic Sciences and Assessment, SLU, Uppsala, Sweden.
    Schindler, Markus
    Department of Aquatic Ecology, EAWAG, Swiss Federal Institute of Aquatic Science and Technology, and Institute of Integrative Biology (IBZ), ETH Zurich, 6047 Kastanienbaum, Switzerland.
    Gessner, Mark O
    Department of Aquatic Ecology, EAWAG, Swiss Federal Institute of Aquatic Science and Technology, and Institute of Integrative Biology (IBZ), ETH Zurich, 6047 Kastanienbaum, Switzerland.
    Malmqvist, Björn
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Placing biodiversity and ecosystem functioning in context: environmental perturbations and the effects of species richness in a stream field experiment2009Ingår i: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 160, nr 4, s. 757-770Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Greater biodiversity is often associated with increased ecosystem process rates, and is expected to enhance the stability of ecosystem functioning under abiotic stress. However, these relationships might themselves be altered by environmental factors, complicating prediction of the effects of species loss in ecosystems subjected to abiotic stress. In boreal streams, we investigated effects of biodiversity and two abiotic perturbations on three related indices of ecosystem functioning: leaf decomposition, detritivore leaf processing efficiency (LPE) and detritivore growth. Replicate field enclosures containing leaves and detritivore assemblages were exposed to liming and nutrient enrichment, raising pH and nutrient levels. Both treatments constitute perturbations for our naturally acidic and nutrient-poor streams. We also varied detritivore species richness and density. The effects of the abiotic and diversity manipulations were similar in magnitude, but whereas leaf decomposition increased by 18% and 8% following liming and nutrient enrichment, respectively, increased detritivore richness reduced leaf decomposition (6%), detritivore LPE (19%) and detritivore growth (12%). The detritivore richness effect on growth was associated with negative trait-independent complementarity, indicating interspecific interference competition. These interactions were apparently alleviated in both enriched and limed enclosures, as trait-independent complementarity became less negative. LPE increased with detritivore density in the monocultures, indicating benefits of intra-specific aggregation that outweighed the costs of intra-specific competition, and dilution of these benefits probably contributed to lowered leaf decomposition in the species mixtures. Finally, the effects of liming were reduced in most species mixtures relative to the monocultures. These results demonstrate how environmental changes might regulate the consequences of species loss for functioning in anthropogenically perturbed ecosystems, and highlight potential influences of biodiversity on functional stability. Additionally, the negative effects of richness and positive effects of density in our field study were opposite to previous laboratory observations, further illustrating the importance of environmental context for biodiversity-ecosystem functioning relationships.

  • 23.
    Nilsson, Karin A.
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Lundback, Sow
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Postavnicheva-Harri, Alexandra
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Persson, Lennart
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Guppy populations differ in cannibalistic degree and adaptation to structural environments2011Ingår i: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 167, nr 2, s. 391-400Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    There is considerable variation in cannibalism between different species and also between individuals of different species, although relatively little is known about what creates this variation. We investigated the degree of cannibalism in guppy (Poecilia reticulata) populations originating from high and low predation environments in Trinidad, and also how cannibalism was affected by the presence of refuges. Females from two populations were allowed to feed on juveniles from two populations in aquaria trials. The cannibalism was size-dependent and varied depending on both juvenile and female origin. Low predation females were more efficient cannibals and low predation juveniles were better at avoiding cannibalism compared to high predation guppies when no refuges were present. The high predation females were superior cannibals and the high predation juveniles were better at escaping cannibalism than the low predation guppies when refuges were present. We discuss whether the differences in cannibalism and response to refuge addition relate to predation-induced habitat shifts and differences in the guppies' natural environment.

  • 24.
    Olofsson, Johan
    et al.
    Division of Biology, Imperial College London, Silwood Park, Ascot, UK.
    de Mazancourt, C.
    Crawley, M.J.
    Spatial heterogeneity and plant species richness at different spatial scales under rabbit grazing2008Ingår i: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 156, nr 4, s. 825-834Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Herbivores influence spatial heterogeneity in soil resources and vegetation in ecosystems. Despite increasing recognition that spatial heterogeneity can drive species richness at different spatial scales, few studies have quantified the effect of grazing on spatial heterogeneity and species richness simultaneously. Here we document both these variables in a rabbit-grazed grassland. We measured mean values and spatial patterns of grazing intensity, rabbit droppings, plant height, plant biomass, soil water content, ammonia and nitrate in sites grazed by rabbits and in matched, ungrazed exclosures in a grassland in southern England. Plant species richness was recorded at spatial scales ranging between 0.0001 and 150 m2. Grazing reduced plant height and plant biomass but increased levels of ammonia and nitrate in the soil. Spatial statistics revealed that rabbit-grazed sites consisted of a mixture of heavily grazed patches with low vegetation and nutrient-rich soils (lawns) surrounded by patches of high vegetation with nutrient-poor soils (tussocks). The mean patch size (range) in the grazed controls was 2.1 ± 0.3 m for vegetation height, 3.8 ± 1.8 m for soil water content and 2.8 ± 0.9 m for ammonia. This is in line with the patch sizes of grazing (2.4 ± 0.5 m) and dropping deposition (3.7 ± 0.6 m) by rabbits. In contrast, patchiness in the ungrazed exclosures had a larger patch size and was not present for all variables. Rabbit grazing increased plant species richness at all spatial scales. Species richness was negatively correlated with plant height, but positively correlated to the coefficient of variation of plant height at all plot sizes. Species richness in large plots (<25 m2) was also correlated to patch size. This study indicates that the abundance of strong competitors and the nutrient availability in the soil, as well as the heterogeneity and spatial pattern of these factors may influence species richness, but the importance of these factors can differ across spatial scales.

  • 25. Palmroth, Sari
    et al.
    Holm Bach, Lisbet
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Nordin, Annika
    Palmqvist, Kristin
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Nitrogen-addition effects on leaf traits and photosynthetic carbon gain of boreal forest understory shrubs2014Ingår i: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 175, nr 2, s. 457-470Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Boreal coniferous forests are characterized by fairly open canopies where understory vegetation is an important component of ecosystem C and N cycling. We used an ecophysiological approach to study the effects of N additions on uptake and partitioning of C and N in two dominant understory shrubs: deciduous Vaccinium myrtillus in a Picea abies stand and evergreen Vaccinium vitis-idaea in a Pinus sylvestris stand in northern Sweden. N was added to these stands for 16 and 8 years, respectively, at rates of 0, 12.5, and 50 kg N ha(-1) year(-1). N addition at the highest rate increased foliar N and chlorophyll concentrations in both understory species. Canopy cover of P. abies also increased, decreasing light availability and leaf mass per area of V. myrtillus. Among leaves of either shrub, foliar N content did not explain variation in light-saturated CO2 exchange rates. Instead photosynthetic capacity varied with stomatal conductance possibly reflecting plant hydraulic properties and within-site variation in water availability. Moreover, likely due to increased shading under P. abies and due to water limitations in the sandy soil under P. sylvestris, individuals of the two shrubs did not increase their biomass or shift their allocation between above- and belowground parts in response to N additions. Altogether, our results indicate that the understory shrubs in these systems show little response to N additions in terms of photosynthetic physiology or growth and that changes in their performance are mostly associated with responses of the tree canopy.

  • 26.
    Persson, Lennart
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Elliott, J. Malcolm
    Population variation and individual maximum size in two leech populations: energy extraction from cannibalism or niche widening?2013Ingår i: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 172, nr 1, s. 119-127Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The theory of cannibal dynamics predicts a link between population dynamics and individual life history. In particular, increased individual growth has, in both modeling and empirical studies, been shown to result from a destabilization of population dynamics. We used data from a long-term study of the dynamics of two leech (Erpobdella octoculata) populations to test the hypothesis that maximum size should be higher in a cycling population; one of the study populations exhibited a delayed feedback cycle while the other population showed no sign of cyclicity. A hump-shaped relationship between individual mass of 1-year-old leeches and offspring density the previous year was present in both populations. As predicted from the theory, the maximum mass of individuals was much larger in the fluctuating population. In contrast to predictions, the higher growth rate was not related to energy extraction from cannibalism. Instead, the higher individual mass is suggested to be due to increased availability of resources due to a niche widening with increased individual body mass. The larger individual mass in the fluctuating population was related to a stronger correlation between the densities of 1-year-old individuals and 2-year-old individuals the following year in this population. Although cannibalism was the major mechanism regulating population dynamics, its importance was negligible in terms of providing cannibalizing individuals with energy subsequently increasing their fecundity. Instead, the study identifies a need for theoretical and empirical studies on the largely unstudied interplay between ontogenetic niche shifts and cannibalistic population dynamics.

  • 27.
    Stenberg, Johan A
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi, miljö och geovetenskap.
    Witzell, Johanna
    Umeå Plant Science Centre, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Ericson, Lars
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi, miljö och geovetenskap.
    Tall herb herbivory resistance reflects historic exposure to leaf beetles in a boreal archipelago age-gradient.2006Ingår i: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 148, nr 3, s. 414-425Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, we introduce the coevolution-by-coexistence hypothesis which predicts that the strength of a coevolutionary adaptation will become increasingly apparent as long as the corresponding selection from an interacting counterpart continues. Hence, evolutionary interactions between plants and their herbivores can be studied by comparing discrete plant populations with known history of herbivore colonization. We studied populations of the host plant, Filipendula ulmaria (meadow sweet), on six islands, in a Bothnian archipelago subject to isostatic rebound, that represent a spatio-temporal gradient of coexistence with its two major herbivores, the specialist leaf beetles Galerucella tenella and Altica engstroemi. Regression analyses showed that a number of traits important for insect-plant interactions (leaf concentrations of individual phenolics and condensed tannins, plant height, G. tenella adult feeding and oviposition) were significantly correlated with island age. First, leaf concentrations of condensed tannins and individual phenolics were positively correlated with island age, suggesting that plant resistance increased after herbivore colonization and continued to increase in parallel to increasing time of past coexistence, while plant height showed a reverse negative correlation. Second, a multi-choice experiment with G. tenella showed that both oviposition and leaf consumption of the host plants were negatively correlated with island age. Third, larvae performed poorly on well-defended, older host populations and well on less-defended, younger populations. Thus, no parameter assessed in this study falsifies the coevolution-by-coexistence hypothesis. We conclude that spatio-temporal gradients present in rising archipelagos offer unique opportunities to address evolutionary interactions, but care has to be taken as abiotic (and other biotic) factors may interact in a complicated way.

  • 28. Wallander , H
    et al.
    Mörth , CM
    Giesler , Reiner
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi, miljö och geovetenskap.
    Increasing abundance of soil fungi is a driver for N-15 enrichment in soil profiles along a chronosequence undergoing isostatic rebound in northern Sweden2009Ingår i: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 160, nr 1, s. 87-96Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Soil organic material (SOM) is usually enriched in N-15 in deeper soil layers. This has been explained by discrimination against the heavier isotope during decomposition or by the accumulation of N-15-enriched microbial biomass versus plant biomass in older SOM. In particular, ectomycorrhizal (EM) fungi have been suggested to accumulate in old SOM since this group is among the most N-15-enriched components of the microbial community. In the present study we investigated the microbial community in soil samples along a chronosequence (7,800 years) of sites undergoing isostatic rebound in northern Sweden. The composition of the microbial community was analyzed and related to the delta N-15 and delta C-13 isotope values of the SOM in soil profiles. A significant change in the composition of the microbial community was found during the first 2,000 years, and this was positively related to an increase in the delta N-15 values of the E and B horizons in the mineral soil. The proportion of fungal phospholipid fatty acids increased with time in the chronosequence and was positively related to the N-15 enrichment of the SOM. The increase in delta C-13 in the SOM was much less than the increase in delta N-15, and delta C-13 values in the mineral soil were only weakly related to soil age. The C:N ratio and the pH of the soil were important factors determining the composition of the microbial community. We suggest that the N being transported from the soil to aboveground tissue by EM fungi is a driver for N-15 enrichment of soil profiles.

  • 29.
    Zackrisson, O
    et al.
    Swedish University of Agricultural Sciences Department of Forest Ecology and Management, Umeå, Sweden.
    Deluca, T
    Swedish University of Agricultural Sciences Department of Forest Ecology and Management, Umeå, Sweden.
    Gentili, Francesco
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysiologisk botanik. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Umeå Plant Science Centre (UPSC).
    Sellstedt, Anita
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysiologisk botanik. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Umeå Plant Science Centre (UPSC).
    Jäderlund, A
    Swedish University of Agricultural Sciences Department of Forest Ecology and Management, Umeå, Sweden.
    Nitrogen fixation in mixed Hylocomium splendens moss communities2009Ingår i: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 160, nr 2, s. 309-319Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The pleurocarpus feather moss, Hylocomium splendens, is one of two co-dominant moss species in boreal forest ecosystems and one of the most common mosses on earth, yet little is known regarding its capacity to host cyanobacterial associates and thus contribute total ecosystem N. In these studies, we evaluated the N-fixation potential of the H. splendens-cyanobacteria association and contrasted the N-fixation activity with that of the putative N-fixing moss-cyanobacteria association of Pleurozium schreberi. Studies were conducted to: quantify N-fixation in H. splendens and P. schreberi in sites ranging from southern to northern Fennoscandia; assess N and P availability as drivers of N-fixation rates; contrast season-long N-fixation rates for both mosses; and characterize the cyanobacteria that colonize shoots of H. splendens. Nitrogen-fixation rates were generally low at southern latitudes and higher at northern latitudes (64-69 degrees N) potentially related to anthropogenic N deposition across this gradient. Nitrogen fixation in H. splendens appeared to be less sensitive to N deposition than P. schreberi. The season-long assessment of N-fixation rates at a mixed feather moss site in northern Sweden showed that H. splendens fixed a substantial quantity of N, but about 50% less total N compared to the contribution from P. schreberi. In total, both species provided 1.6 kg fixed N ha(-1) year(-1). Interestingly, H. splendens demonstrated somewhat higher N-fixation rates at high fertility sites compared to P. schreberi. Nostoc spp. and Stigonema spp. were the primary cyanobacteria found to colonize H. splendens and P. schreberi. These results suggest that H. splendens with associated Nostoc or Stigonema communities contributes a significant quantity of N to boreal forest ecosystems, but the contribution is subordinate to that of P. schreberi at northern latitudes. Epiphytic cyanobacteria are likely a key factor determining the co-dominant presence of these two feather mosses across the boreal biome.

  • 30.
    Zhang, Yixin
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi och geovetenskap.
    Balancing food availability and hydrodynamic constraint: phenotypic plasticity and growth in Simulium noelleri blackfly larvae.2006Ingår i: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 147, nr 1, s. 39-46Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Organisms through phenotypic plasticity can cope with multiple changed environmental conditions. Theory predicts that animals in streams and rivers should be able to balance demands of the needs to obtain food efficiently and to adjust response to hydrodynamic variability. This study examined effects of variations in food availability and current velocity on the feeding structure and growth rate of Simulium noelleri blackfly larvae. The larvae developed larger labral fans and more rays under slow current and low food regimes than in fast current and high food conditions. In both fast and slow current regimes, growth rates were higher and development periods to the final-instar stage were shorter in high food treatments. The estimated flux rates of food particles through labral fans under high food treatments for both fast and slow current regimes were higher than those under low food treatments. Although both food and current velocity appeared to have selected for flexibility of feeding structure and growth rate, food availability was a more important factor for phenotypic and developmental plasticity than current velocity. The results indicate a strong link between environmental changes in food availability and current velocity, phenotypic plasticity, and growth rate of S. noelleri. This study suggests that plasticity of ecomorphs with macroevolutionary significance may play a role in the early evolutionary stages of blackfly larvae.

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