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  • 1.
    Backéus, Ingvar
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecological Botany.
    Bog vegetation re-Mapped after sixty years: Studies on Skagershultamossen, central Sweden1972In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 23, no 3, p. 384-393Article in journal (Refereed)
    Abstract [en]

    The author has re-mapped two areas on Skagershultamossen. The new maps have been compared with maps of the same areas from 1910, made by L. von Post. The vegetation changes are small. The open water surfaces have diminished in number and extent. The theory of cyclic succession on peat bogs finds no support from the maps. Plant communities have been delimited as to correspond to those on the old maps and defined through analysis of a number of sample plots

  • 2.
    Berglund, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Animal Ecology.
    Sex dimorphism and skewed sex-ratios in the prawn species Palaemon adspersus and P. squilla1981In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 36, no 2, p. 158-162Article in journal (Refereed)
  • 3.
    Berglund, Anders
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Animal Ecology.
    Rosenqvist, Gunilla
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolutionary Biology, Animal Ecology.
    Reproductive costs in the prawn Palaemon adspersus: effects on growth and predator vulnerability1986In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 46, no 3, p. 349-354Article in journal (Refereed)
  • 4.
    Berglund, Anders
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Animal Ecology.
    Rosenqvist, Gunilla
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Animal Ecology.
    Svensson, Ingrid
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Animal Ecology.
    Multiple matings and paternal brood care in the pipefish Syngnathus typhle1988In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 51, no 2, p. 184-188Article in journal (Refereed)
  • 5.
    Björklund, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology.
    Are comparative analyses always necessary?1997In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 80, p. 607-612Article in journal (Refereed)
  • 6.
    Björklund, Mats
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Animal Ecology.
    Bergek, Sara
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Animal Ecology.
    On the relationship between population differentiation and sampling effort: is more always better?2009In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 118, no 8, p. 1127-1129Article in journal (Refereed)
    Abstract [en]

    Given the relative ease by which genotypic data now can be obtained, studies of population differentiation can attain high statistical power provided the number of individuals and loci scored are sufficiently high. This has led to a misunderstanding of the concept of power, and studies with a low number of individuals and loci are dismissed despite highly significant results. This raises statistical, biological and ethical concerns, which we discuss in this note. We suggest that authors should routinely report the number of additional non-significant loci as a measure of the robustness of the results.

  • 7.
    Bolmgren, Kjell
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Ecological Botany.
    Cowan, Peter D.
    Time – size tradeoffs: a phylogenetic comparative study of flowering time, plant height and seed mass in a north-temperate flora2008In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 117, no 3, p. 424-429Article in journal (Refereed)
    Abstract [en]

    Parents face a timing problem as to when they should begin devoting resources from their own growth and survival to mating and offspring development. Seed mass and number, as well as maternal survival via plant size, are dependent on time for development. The time available in the favorable season will also affect the size of the developing juveniles and their survival through the unfavorable season. Flowering time may thus represent the outcome of such a time partitioning problem. We analyzed correlations between flowering onset time, seed mass, and plant height in a north-temperate flora, using both cross-species comparisons and phylogenetic comparative methods. Among perennial herbs, flowering onset time was negatively correlated with seed mass (i.e. plants with larger seeds started flowering earlier) while flowering onset time was positively correlated with plant height. Neither of these correlations was found among woody plants. Among annual plants, flowering onset time was positively correlated with seed mass. Cross-species and phylogenetically informed analyses largely agreed, except that flowering onset time was also positively correlated with plant height among annuals in the cross-species analysis. The different signs of the correlations between flowering onset time and seed mass (compar. gee regression coefficient=−7.8) and flowering onset time and plant height (compar. gee regression coefficient=+30.5) for perennial herbs, indicate that the duration of the growth season may underlie a tradeoff between maternal size and offspring size in perennial herbs, and we discuss how the partitioning of the season between parents and offspring may explain the association between early flowering and larger seed mass among these plants.

  • 8. Bourdeau, Paul E.
    et al.
    Johansson, Frank
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Population and Conservation Biology.
    Predator-induced morphological defences as by-products of prey behaviour: a review and prospectus2012In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 121, no 8, p. 1175-1190Article, review/survey (Refereed)
    Abstract [en]

    Predator-induced morphological defences (PIMDs) are ubiquitous. Many PIMDs may be mediated by prey behaviour rather than directly cued by predators. A survey of 92 studies indicated 40 that quantified prey behaviour, all of which document positive associations between defence production and activity reduction. Thus, PIMDs are associated with changes in prey activity, which could have caused the morphological change. We propose two possible mechanisms: 1) decreased activity reduces feeding rate, resulting in lower growth and morphological change; and 2) activity reduction conserves energy, which is reallocated for growth, subsequently changing morphology. Resource availability also causes similar morphological change to predator presence, suggesting confounding effects of resources and predators with current methodology. Future studies should estimate food ingestion, assimilation efficiency, and growth rate in the presence and absence of predators, crossing predator presence with resource levels. Not all PIMDs will be behaviourally-mediated, but consideration of causal linkages between prey behaviour and PIMDs is warranted.

  • 9.
    Candolin, Ulrika
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Limnology.
    Engström-Öst, Jonna
    Salesto, Tiina
    Human-induced eutrophication enhances reproductive success through effects on parenting ability in sticklebacks2008In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 117, no 3, p. 459-465Article in journal (Refereed)
    Abstract [en]

    Human-induced processes are altering habitats at an unprecedented rate and scale. This has changed the biodiversity and biomass in many areas, but also led to phenotypic and genetic alterations of populations. Here we investigated the effects of the ongoing eutrophication in the Baltic Sea on the reproductive success of threespine stickleback males Gasterosteus aculeatus, through effects on reproductive behaviour and parenting ability. We allowed males to complete breeding cycles in a competitive setting under increased macro algae cover or increased turbidity caused by phytoplankton growth. Both environmental factors improved the parenting ability of the males and enhanced reproductive output. Increased alga growth and turbidity reduced aggressive interactions between males during the parental phase, probably due to reduced visibility, which slowed down a deterioration of condition. This increased the reproductive lifespan of the males and enabled them to complete more breeding cycles, as found when males were allowed to complete as many breeding cycles as they could under increased algae cover. In addition, increased turbidity improved oxygen conditions, which enhanced hatching success and reduced the need for vigorous fanning behaviour. Increased turbidity, however, relaxed selection on male size. Together with earlier results on relaxed sexual selection under changed environmental conditions, this suggests that the effect of eutrophication on stickleback populations is complex. It increases the reproductive output of populations, since more individuals are spawning within eutrophicated areas and their hatching success is increased, but it relaxes sexual and natural selection at the reproductive stage. Whether this will shift selection and population regulation to other life stages, such as the juvenile stage, deserves further investigations.

  • 10. Cichon, M
    et al.
    Merilä, Juha
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolutionary Biology, Population Biology.
    Hillström, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolutionary Biology, Animal Ecology.
    Wiggins, David
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolutionary Biology, Animal Ecology.
    Mass-dependent mass loss in breeding birds: getting the null hypothesis right1999In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 87, no 1, p. 191-194Article in journal (Refereed)
    Abstract [en]

    An assumption central to many tests of statistical association between two variables is the null expectation of zero association. Here, we draw attention to the fact that in many published tests of mass-dependent mass loss in breeding birds, this assumption has been violated. We show that a correct null hypothesis can be derived by using resampling methods, and analyse three data sets (two previously published) from passerine birds to illustrate the approach. Our results show, that under a correct null hypothesis, the biological interpretation of the previously published results is reversed-initially heavy birds do actually lose less mass (relative to their weight) than the initially light birds.

  • 11.
    Ehrlén, Johan
    et al.
    Dept of Botany, Stockholm Univ..
    Käck, Sofia
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Ecological Botany.
    Ågren, Jon
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Ecological Botany.
    Pollen limitation, seed predation and scape length in Primula farinosa2002In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 97, no 1, p. 45-51Article in journal (Refereed)
    Abstract [en]

    Floral display and reward production may affect the attractiveness of a plant to a range of interacting animals including pollinators, herbivores, and vectors of pathogenic fungi. The optimal floral phenotype should therefore depend on the relative importance of selection exerted by both mutualistic and antagonistic animals. The perennial, rosette herb Primula farinosa is polymorphic for scape length. Natural populations may include both plants with flowers displayed well above the ground (the long-scaped morph) and those with flowers positioned very close to the ground (the short-scaped morph). In this study, we conducted a field experiment to examine how the relative fitness of the two scape morphs is affected by interactions with pollinators and fruit predators in two different microhabitats (high and low vegetation). As predicted based on the difference in floral display, supplemental hand-pollination showed that fruit initiation was more strongly pollen-limited in the short-scaped than in the long-scaped morph, and that this difference was significantly larger in high than in low vegetation. Moreover, plants with a short scape experienced lower levels of fruit predation than plants with a long scape. Among open-pollinated controls, there was no significant difference in seed output between the two scape morphs. However, among plants receiving supplemental hand-pollination, short-scaped plants produced significantly more seeds than long-scaped plants. The results suggest that the positive and negative effects of a prominent floral display (increased pollination and seed predation, respectively) balance in the study population, but also that the short-scaped morph would have an advantage at higher pollination intensities. Spatial and temporal variation in pollinator activity and seed predation should result in associated variation in the relative fecundity of the two scape morphs.

  • 12.
    Eklöv, Peter
    et al.
    Lund University, Department of limnology.
    Hamrin, Stellan F
    Lund University, Department of limnology.
    PREDATORY EFFICIENCY AND PREY SELECTION - INTERACTIONS BETWEEN PIKE ESOX-LUCIUS, LUCIUS, PERCH PERCA-FLUVIATILIS AND RUDD SCARDINUS-ERYTHROPHTHALMUS1989In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 56, no 2, p. 149-156Article in journal (Refereed)
  • 13.
    Frost, Ingela
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecological Botany.
    Rydin, Håkan
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecological Botany.
    Effects of competition, grazing and cotyledon nutrient supply on growth of Quercus robur seedlings1997In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 79, no 1, p. 53-58Article in journal (Refereed)
    Abstract [en]

    In this greenhouse experiment we examined how competition and herbivory affects the growth of Quercus robur seedlings and if the cotyledon nutrient reserve is of importance for survival and growth during unfavourable conditions. We planted oak seedlings with or without a strong competitor (grass turf) and subjected them to factorial grazing and cotyledon removal, in a split-plot design. After one growing season (20 weeks) we found large negative main effects from competition, grazing and cotyledon removal on all biomass components of the seedling. Seedling mortality was also significantly increased by competition. We observed an additional effect of cotyledon removal if the seedlings were also grazed or were growing in competition with grass. This gives some support to the hypothesis that cotyledon nutrient reserves are used under unfavourable conditions, but the effect was often relatively small and not detectable in the growth of all plant parts.

  • 14.
    Griesser, Michael
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Evolutionary Biology. Univ Zurich, Dept Anthropol;Univ Bern, Inst Ecol & Evolut.
    Mourocq, Emeline
    Univ Zurich, Dept Anthropol;Univ Bern, Inst Ecol & Evolut.
    Barnaby, Jonathan
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Evolutionary Biology.
    Bowgen, Katharine M.
    Bournemouth Univ, Fac Sci & Technol, Dept Life & Environm Sci.
    Eggers, Sonke
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Evolutionary Biology. Swedish Univ Agr Sci, Dept Ecol.
    Fletcher, Kevin
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology.
    Kozma, Radoslav
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology.
    Kurz, Franziska
    Laurila, Anssi
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology.
    Nystrand, Magdalena
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Evolutionary Biology.
    Sorato, Enrico
    Linkoping Univ, IFM Biol..
    Ekman, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology.
    Experience buffers extrinsic mortality in a group-living bird species2017In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 126, no 9, p. 1258-1268Article in journal (Refereed)
    Abstract [en]

    Extrinsic mortality has a strong impact on the evolution of life-histories, prey morphology and behavioural adaptations, but for many animals the causes of mortality are poorly understood. Predation is an important driver of extrinsic mortality and mobile animals form groups in response to increased predation risk. Furthermore, in many species juveniles suffer higher mortality than older individuals, which may reflect a lower phenotypic quality, lower competitiveness, or a lack of antipredator or foraging skills. Here we assessed the causes of mortality for 371 radio tagged Siberian jays. This sedentary bird species lives in family groups that contain a breeding pair as well as related and unrelated non-breeders. Ninety-five percent of death were due to predation (n = 59 out of 62 individuals) and most individuals were killed by Accipiter hawks. Multivariate Cox proportional hazards models showed that non-breeders had a lower survival than breeders, but only in territories in managed forest with little visual cover. Examining breeders, only sex influenced survival with males having a lower survival than females. For non-breeders, juveniles had lower survival than older non-breeders, and those on managed territories had lower survival than those on unmanaged territories. Additionally, a low feather quality reduced the survival probability of non-breeders only. Thus, living on managed territories and having a low feature quality affected only non-breeders, particularly juveniles. These findings add to previous research demonstrating that juvenile Siberian jays acquire critical antipredator skills from experienced group members. Thus, experience can buffer extrinsic mortality, highlighting that group living not only provides safety in numbers, but also provide social opportunities to learn critical life-skills.

  • 15.
    Henriksson,, Lars Eric
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Faculty of Mathematics and Science.
    Enckell, Pehr H.
    Henriksson, Elisabet
    Uppsala University, Disciplinary Domain of Science and Technology, Faculty of Mathematics and Science.
    Determination of the Nitrogen-Fixing Capacity of Algae in Soil1972In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 23, no 3, p. 420-423Article in journal (Refereed)
    Abstract [en]

    A method to determine the potential of microbial nitrogen fixation in soils under aerobic conditions is described. Four different soil types were studied; loess, lime, mull and calcareous soil. The soil samples were collected in three different areas in Europe.

  • 16. Hettyey, Attila
    et al.
    Zsarnoczai, Szilvia
    Vincze, Krisztina
    Hoi, Herbert
    Laurila, Anssi
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Population and Conservation Biology.
    Interactions between the information content of different chemical cues affect induced defences in tadpoles2010In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 119, no 11, p. 1814-1822Article in journal (Refereed)
    Abstract [en]

    Animals often alter their behaviour, morphology and physiology in the presence of predators. These induced defences can be fine-tuned by a variety of environmental factors such as predator species, acute predation risk or food availability. It has, however, remained unclear what cues influence the extent and quality of induced defences and how the information content of these cues interact to determine the development of antipredator defences. We performed an experiment to study the significance of direct chemical cues, originating from the predators themselves, and indirect cues, released by attacked or consumed prey, for phenotypic responses in Rana dalmatina tadpoles. We reared tadpoles in the presence of caged predators (Triturus vulgaris, Aeshna cyanea) fed either one or three tadpoles every other day outside the tadpole-rearing tanks. Fifteen hours after food provisioning, predators were put back into the tanks containing focal tadpoles either after washing (direct + digestion-released cues) or with the water containing remnants of the prey (direct + all types of indirect cues). Our results suggest that direct cues together with digestion-released cues can be sufficient to induce strong antipredator responses. Induced defences depended on both direct cues, affecting predator-specific responses, and the quantity of indirect cues, resulting in graded responses to differences in predation threat. Moreover, direct and indirect cues interacted in behaviour, resulting in predator-specific graded responses. We also observed a decrease in the extent of predator-induced responses in large tadpoles as compared to small ones. Our results, thus, suggest that prey integrate multiple cues about predators to optimize induced defences and that this process changes during ontogeny.

  • 17.
    Hillebrand, Helmut
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Limnology.
    DeMontpellier, Geraldine
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Limnology.
    Liess, Antonia
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Limnology.
    Effects of macrograzers and light on periphyton stoichiometry2004In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 106, no 1, p. 93-104Article in journal (Refereed)
    Abstract [en]

    Ecological stoichiometry describes the biochemical constraints of trophic interactions emerging from the different nutrient content and nutrient demand of producers and consumers, respectively. Most research on this topic originates from well-mixed pelagic food webs, whereas the idea has received far less attention in spatially structured habitats. Here, we test how light as well as grazing and nutrient regeneration by consumers affects growth and biomass of benthic primary producers. In the first laboratory experiment, we manipulated grazer presence (two different snail species plus ungrazed control), in the second experiment we factorially combined manipulation of grazer presence and light intensity. We monitored snail and periphyton biomass as well as dissolved and particulate nutrients (nitrogen and phosphorus) over time. Grazers significantly reduced algal biomass in both experiments. Grazers affected periphyton nutrient content depending on the prevailing nutrient limitation and their own body stoichiometry. In the nitrogen (N-) limited first experiment, grazers increased N both in the periphyton and in the water column. The effect was stronger for grazers with lower N-content. In the phosphorus (P-) limited second experiment, grazers increased the P-content of the periphyton, but the grazer with lower N-content had additionally positive effects on algal N. Light reduction did not affect periphyton biomass, but increased chlorophyll-, N- and P-content of the periphyton. These experiments revealed that the indirect effects of grazers on periphyton were bound by stoichiometric constraints of nutrient incorporation and excretion.

  • 18. Hoglund, J
    Can mating systems affect local extinction risks?: Two examples of lek-breeding waders1996In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 77, no 2, p. 184-188Article in journal (Refereed)
  • 19. Hoglund, J
    et al.
    Sheldon, B C
    The cost of reproduction and sexual selection1998In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 83, no 3, p. 478-483Article in journal (Refereed)
  • 20. Hoglund, J
    et al.
    Widemo, F
    Sutherland, W J
    Nordenfors, H
    Ruffs, Philomachus pugnax, and distribution models: can leks be regarded as patches?1998In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 82, no 2, p. 370-376Article in journal (Refereed)
  • 21. Jankowski, Thomas
    et al.
    Weyhenmeyer, Gesa A.
    The role of spatial scale and area in determining richness-altitude gradients in Swedish lake phytoplankton communities2006In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 115, no 3, p. 433-442Article in journal (Refereed)
  • 22. Jones, Adam G.
    et al.
    Rosenqvist, Gunilla
    Berglund, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Animal Ecology.
    Avise, John C.
    Mate quality influences multiple maternity in the sex-role-reversed pipefish Syngnathus typhle2000In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 90, no 2, p. 321-326Article in journal (Refereed)
    Abstract [en]

    In the pipefish Syngnathus typhle, pregnant males provide all parental care. Females are able to produce more eggs than males can brood, and consequently females compete more intensely for mates than do males, a phenomenon defined as sex-role reversal. As the genetic mating system influences the operation of sexual selection, we investigate variation in one phenotypic component of mate quality, female body size, as a possible proximate influence on mating system variation in S. typhle. Breeding trials were employed, each consisting of a single receptive male with four adult females. In each replicate, a focal male was paired either with a set of small or with a set of large females. Males were allowed to mate freely, and after several weeks of brood development, maternity of the progeny was resolved using three microsatellite loci. Males with access either to small or to large females successfully mated with a mean of 2.1 or 1.3 females, respectively, a significant difference. Results indicate that variation in female size can affect the mating system and thereby influence sexual selection in pipefish. Thus, the high rate of multiple mating by S. typhle males in the wild may be explained in part by the extensive size variation in naturally occurring, sexually mature females.

  • 23. Laing, C. G.
    et al.
    Granath, G.
    Belyea, L. R.
    Allton, K. E.
    Rydin, Håkan
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Plant Ecology and Evolution.
    Tradeoffs and scaling of functional traits in Sphagnum as drivers of carbon cycling in peatlands2014In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 123, no 7, p. 817-828Article in journal (Refereed)
    Abstract [en]

    Growth and decomposition of Sphagnum controls turnover of a large global store of soil organic carbon. We investigated variation in morphological and physiological traits of Sphagnum shoots, and related this variation to canopy variables relevant to peatland carbon cycling. We sampled Sphagnum along a bog plateau-swamp forest gradient and measured a suite of shoot traits and canopy variables. Major axes of variation were identified using principal component analysis and correlated with canopy variables such as growth, biomass and decomposition. We also examined scaling of shoot traits with one another and with canopy variables. Two distinct tradeoffs in shoot traits emerged. From dry to wet habitats, individual metabolic rates and capitulum size increased while numerical density decreased, leading to faster growth and elongation on an individual basis. From treed to open habitats, photosynthetic efficiency decreased and photosynthetic biomass increased, driving faster growth on an area basis and slower litter mass loss. The tradeoffs identified have important implications for peatlands undergoing climate-related changes in water and light availability. Sphagnum trait comparisons, combined with scaling analyses, offer a promising approach to understanding and predicting the effects of environmental change on peatland carbon cycling.

  • 24.
    Liess, Antonia
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Limnology.
    Diehl, Sebastian
    Effects of enrichment on protist abundances and bacterial composition in simple microbial communities2006In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 114, no 1, p. 15-26Article in journal (Refereed)
    Abstract [en]

    We experimentally investigated effects of nutrient enrichment and trophic structure in a microbial food web consisting of mixed bacteria, two bacterivorous ciliates (Tetrahymena sp. and Colpidium sp.) and an omnivorous ciliate (Blepharisma sp.) feeding on both trophic levels. We assembled all possible food webs including one or more of the ciliate species and cross-classified them with four levels of enrichment of the bacterial medium. The qualitative outcome of food web interactions was independent of enrichment and always the same: Tetrahjrmena strongly depressed or excluded Colpidium, and Blepharisma strongly depressed or excluded both bacterivores. Consequently, in all sub-webs only the dominant ciliate species responded positively to enrichment. The total density of bacteria increased with enrichment irrespective of food web composition. In contrast, the response of singlecelled bacteria to enrichment depended on food web composition and was only weakly positive in most food webs with the omnivore. Enrichment had a positive effect on the relative success of (presumably more defended) bacterial aggregates. The outcome of interspecific interactions among ciliates could not be predicted from monoculture experiments and deviated from earlier experiments in which each bacterivore coexisted separately with the omnivore. As a potential explanation we suggest that changes in experimental protocol reduced spatial heterogeneity and increased attack rates. A simple, dynamical model shows that increased attack rates can indeed greatly decrease the upper limit and range of enrichment over which intermediate consumers can coexist with omnivores.

  • 25.
    Liess, Antonia
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Limnology.
    Olsson, Jens
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Limnology.
    Quevedo, Mario
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Limnology.
    Eklöv, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Limnology.
    Vrede, Tobias
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Limnology.
    Hillebrand, Helmut
    Food web complexity affects stoichiometric and trophic interactions2006In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 114, no 1, p. 117-125Article in journal (Refereed)
    Abstract [en]

    The stoichiometry of trophic interactions has mainly been studied in simple consumer–prey systems, whereas natural systems often harbour complex food webs with abundant indirect effects. We manipulated the complexity of trophic interactions by using simple laboratory food webs and complex field food webs in enclosures in Lake Erken. In the simple food web, one producer assemblage (periphyton) and its consumers (benthic snails) were amended by perch, which was externally fed by fish food. In the complex food web, two producer assemblages (periphyton and phytoplankton), their consumers (benthic invertebrates and zooplankton) and perch feeding on zooplankton were included. In the simple food web perch affected the stoichiometry of periphyton and increased periphyton biomass and the concentration of dissolved inorganic nitrogen. Grazers reduced periphyton biomass but increased its nutrient content. In the complex food web, in contrast to the simple food web, perch affected periphyton biomass negatively but increased phytoplankton abundance. Perch had no influence on benthic invertebrate density, zooplankton biomass or periphyton stoichiometry. Benthic grazers reduced periphyton biomass and nutrient content. The difference between the simple and the complex food web was presumably due to the increase of pelagic cyanobacteria (Gloeotrichia sp.) with fish presence in the complex food web, thus fish had indirect negative effects on periphyton biomass through nutrient competition and shading by cyanobacteria. We conclude that the higher food web complexity through the presence of pelagic primary producers (in this case Gloeotrichia sp.) influences the direction and strength of trophic and stoichiometric interactions.

  • 26.
    Løe, Geir
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Ecological Botany.
    Toräng, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Ecological Botany.
    Gauldeul, Myriam
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Ecological Botany.
    Ågren, Jon
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Ecological Botany.
    Trichome production and spatiotemporal variation in herbivory in the perennial herb Arabidopsis lyrata2007In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 116, no 1, p. 134-142Article in journal (Refereed)
    Abstract [en]

    Allocation theory suggests that the optimal level of resistance against herbivores should vary with the risk of herbivory if allocation to resistance is costly. The perennial herb Arabidopsis lyrata has a genetically based polymorphism for- trichome production and occurs in a glabrous and a trichome-producing form. Leaf trichomes (hairs) can protect plants against insect herbivores, and may increase tolerance to drought and UV-radiation. To examine the functional significance of trichome production, we documented the frequency of glabrous plants and damage by insect herbivores in 30 A. lyrata populations in Sweden and Norway. The proportion of glabrous plants ranged from 0.10 to 0.71 (median = 0.44) in polymorphic populations; 7 of 12 populations in Norway and 14 of 18 populations in Sweden were monomorphic glabrous, i.e. with fewer than 5% trichome-producing plants. The mean proportion of the leaf area removed by herbivores varied substantially among populations and years. With few exceptions, glabrous plants were more damaged than trichome-producing plants in polymorphic populations. The intensity of herbivory quantified as the mean damage to glabrous plants tended to be higher in polymorphic populations than in populations monomorphic for the glabrous morph and was higher in Sweden than in Norway. In Norway, both the magnitude of herbivore damage and the frequency of trichome-producing plants tended to decrease with increasing altitude. The results indicate that leaf trichomes contribute to resistance against herbivorous insects in A. lyrata, and suggest that herbivore-mediated selection contributes to the maintenance of the polymorphism in trichome production.

  • 27.
    Marklund, Maria H. K.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology. Water Research Centre and The Environment Institute, School of Biological Sciences, Univ. of Adelaide, North Terrace, SA, Australia.
    Svanbäck, Richard
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology.
    Zha, Yinghua
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Scharnweber, Kristin
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Eklöv, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    The influence of habitat accessibility on the dietary and morphological specialisation of an aquatic predator2018In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 127, no 1, p. 160-169Article in journal (Refereed)
    Abstract [en]

    Individual diet and habitat specialisation are widespread in animal taxa and often related to levels of predation and competition. Mobile consumers such as predatory fish can stabilise lake food webs by ranging over a larger area than their prey, thereby switching between habitats. Although, this switching assumes that the predator has equal preference for the available prey, individual diet specialisation and morphological adaptations to different habitats could potentially prevent individuals from switching between habitats. In this study, we assessed the niche width and individual specialisation in Eurasian perch Perca fluviatilis in response to a shift in habitat use by manipulating the ability for this top predator to couple habitats. We ran an eight weeks pond experiment, to test the effect of habitat switching on diet and morphological specialisations. We show that habitat coupling influenced individual diet specialisation and niche use in expected directions where specialisation increased with decreasing habitat switching. In contrast to expectations, the morphological variation decreased with increasing diet specialisation. Our results expand on previous work and suggest that individual specialisation and niche width can impact the ability of mobile predators to couple habitats. Furthermore, it shows the importance of individual specialisations in relation to habitat coupling.

  • 28.
    Murillo-Rincon, Andrea P.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology. Christian Albrechts Univ Kiel, Inst Zool, Kiel, Germany..
    Laurila, Anssi
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology.
    Orizaola, Germán
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology.
    Compensating for delayed hatching reduces offspring immune response and increases life-history costs2017In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 126, no 4, p. 565-571Article in journal (Refereed)
    Abstract [en]

    Organisms are exposed to multiple sources of stress in nature. When confronted with a stressful period affecting growth and development, compensatory responses allow the restoration of individual fitness, providing an important buffering mechanism against climatic and other environmental variability. However, tradeoffs between increased growth/development and other physiological traits are predicted to prevent these high growth and development rates from becoming constitutive. Here, we investigated how compensatory responses in growth and development affect immune responses. By using low temperature to stop embryonic development, we exposed moor frog Rana arvalis tadpoles to two levels of time-constraints: non-delayed hatching and 12-day delayed hatching. In a common garden experiment, we recorded larval growth and development, as well as their immune response, measured as the inflammatory reaction after the injection of phytohaemagglutinin (PHA). Tadpoles originating from delayed hatching treatments had a lower immune response to PHA challenge than those from the non-delayed hatching treatment. In general, tadpoles from the delayed hatching treatment reached metamorphosis faster and at a smaller size than control tadpoles. However, immune-challenged tadpoles were not able to accelerate their development in response to delayed hatching. Our results indicate that 1) the innate immune response can be reduced in organisms undergoing compensatory developmental responses in growth and development and 2) compensatory capacity can be reduced when organisms are immunologically challenged. These dual findings reveal the complexity of handling multiple stressors and highlight the importance of examining the costs and limits of mounting an immune response in the context of increasing phenological instability ascribed to climate change.

  • 29.
    Naddafi, Rahmat
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Limnology.
    Eklöv, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Limnology.
    Pettersson, Kurt
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Limnology.
    Non-lethal predator effects on the feeding rate and prey selection of the exotic zebra mussel (Dreissena polymorpha)2007In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 116, no 8, p. 1289-1298Article in journal (Refereed)
    Abstract [en]

    Predators may induce changes in prey feeding that indirectly influence both the impact of prey on resource abundances and their interactions with other species in their community. We evaluated whether clearance and excretion (faeces plus pseudofaeces) of phytoplankton by zebra mussels were affected by the presence of predatory cues from roach (Rutilus rutilus) and signal crayfish (Pasifastacus leniusculus). We found that non-lethal effects of predators can alter zebra mussel clearance rate and thus the impact of zebra mussels on phytoplankton. Risk cues released by both predators had similar negative effects on clearance rate of zebra mussels and cascading positive indirect effects on phytoplankton resources. Predation risk had a stronger effect on zebra mussels' clearance rate of cyanobacteria and diatoms than cryptophytes and chrysophytes. The presence of predators did not significantly affect the rate at which zebra mussels expelled and excreted phytoplankton, although there was a tendency for more chlorophyll to be expelled and excreted in the presence of predators. Our results contribute to the growing evidence that predators indirectly affect resource dynamics and food web structure through their non-lethal effects on consumers. Our results suggest that exotic species such as zebra mussels can show behavioural responses to both native (e.g., roach) and exotic (e.g., crayfish) predators.

  • 30.
    Olsson, Jens
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Limnology.
    Svanbäck, Richard
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Limnology.
    Eklöv, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Limnology.
    Growth rate constrain morphological divergence when driven by competition2006In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 115, no 1, p. 15-22Article in journal (Refereed)
    Abstract [en]

    Resource competition has been hypothesized to be important in driving divergence by natural selection. The effect of competition on morphological divergence and plasticity has however rarely been investigated. Since low growth rates might constrain morphological modulation and individual growth rates usually are negatively related to the intensity of competition, there might be a connection between competition, growth rate and morphological divergence. We performed an aquarium experiment with young-of-the-year Eurasian perch (Perca fluviatilis L.) to investigate how individual growth rate affected morphological plasticity induced by contrasting habitat treatments. Furthermore, in a field study of 10 lakes we also related the degree of morphological differentiation between habitats to the intraspecific competitior biomass. In the aquarium experiment we found that morphological plasticity was growth rate dependent in that morphological differentiation between the habitat treatments was confined to high individual growth rates. In the field study we found that morphological differentiation between habitats decreased with increasing intraspecific competitior biomass. Since plasticity is hypothesized to be important in divergence and intraspecific biomass could serve as a proxy for the level of competition, we suggest that our results indicate that morphological divergence might be constrained during periods of intense intraspecific competition due to low growth rates. A possible scenario is that at low growth rates all energy available is used for metabolic maintenance and no surplus energy is therefore available for morphological modulation.

  • 31.
    Orizaola, Germa
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Population and Conservation Biology.
    Dahl, Emma
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Population and Conservation Biology.
    Laurila, Anssi
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Population and Conservation Biology.
    Reversibility of predator-induced plasticity and its effect at a life-history switch point2012In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 121, no 1, p. 44-52Article in journal (Refereed)
    Abstract [en]

    In natural systems, organisms are frequently exposed to spatial and temporal variation in predation risk. Prey organisms are known to develop a wide array of plastic defences to avoid being eaten. If inducible plastic defences are costly, prey living under fluctuating predation risk should be strongly selected to develop reversible plastic traits and adjust their defences to the current predation risk. Here, we studied the induction and reversibility of antipredator defences in common frog Rana temporaria tadpoles when confronted with a temporal switch in predation risk by dragonfly larvae. We examined the behaviour and morphology of tadpoles in experimental treatments where predators were added or withdrawn at mid larval development, and compared these to treatments with constant absence or presence of predators. As previous studies have overlooked the effects that developing reversible anti-predator responses could have later in life (e.g. at life history switch points), we also estimated the impact that changes in antipredator responses had on the timing of and size at metamorphosis. In the presence of predators, tadpoles reduced their activity and developed wider bodies, and shorter and wider tails. When predators were removed tadpoles switched their behaviour within one hour to match that found in the constant environments. The morphology matched that in the constant environments in one week after treatment reversal. All these responses were highly symmetrical. Short time lags and symmetrical responses for the induction/reversal of defences suggest that a strategy with fast switches between phenotypes could be favoured in order to maximise growth opportunities even at the potential cost of phenotypic mismatches. We found no costs of developing reversible responses to predators in terms of life-history traits, but a general cost of the induction of the defences for all the individuals experiencing predation risk during some part of the larval development (delayed metamorphosis). More studies examining the reversibility of plastic defences, including other type of costs (e.g. physiological), are needed to better understand the adaptive value of these flexible strategies.

  • 32.
    Orizaola, German
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Population and Conservation Biology.
    Dahl, Emma
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Population and Conservation Biology.
    Laurila, Anssi
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Population and Conservation Biology.
    Compensating for delayed hatching across consecutive life-history stages in an amphibian2010In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 119, no 6, p. 980-987Article in journal (Refereed)
    Abstract [en]

    Environmental conditions experienced early in the ontogeny can have a strong impact on individual fitness and performance later in life. Organisms may counteract the negative effects of poor developmental conditions by developing compensatory responses in growth and development. However, previous studies on compensatory responses have largely ignored the effects that poor embryonic conditions could have during the later life stages. In this study, we examined the effects of artificially delayed development in early life over two later life history transitions by investigating the compensatory growth of larval moor frogs Rana arvalis in response to temperature variation during embryonic development, and the associated costs during the larval 'and postmetamorphic stages. Low temperature during embryonic stage lead to delayed hatching at smaller size. The groups with delayed embryonic development showed strong compensatory growth during the larval stage, and reached similar metamorphic size than the controls in a shorter time. However, the most strongly delayed group was not able to fully catch up the total development time. These compensatory responses were found in the absence of photoperiod cues indicating that the delay in embryonic development was sufficient to initiate the compensatory response in larval growth and development. No apparent costs of compensatory growth were detected in terms of morphology or locomotor performance at the juvenile stage. We found that compensatory responses can be activated as early as at the embryonic stage and extend over several consecutive life history transitions, mitigating the effects of poor conditions experienced early in development. Potential short-term costs in natural environments and the occurrence of long-term costs, which prevent the generalisation of a faster larval life style, are discussed.

  • 33. Osorio-Zuniga, Felipe
    et al.
    Fonturbel, Francisco E.
    Rydin, Håkan
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Plant Ecology and Evolution.
    Evidence of mutualistic synzoochory between cryptogams and hummingbirds2014In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 123, no 5, p. 553-558Article in journal (Refereed)
    Abstract [en]

    Endozoochory is usually involved in seed dispersal mutualisms, whereas ectozoochory is non-rewarding, and therefore neutral (or even negative) for the animal vector. Synzoochory is an intermediate dispersal type between endo and ectozoochory in which propagules are deliberately transported (usually in the mouth) but with no ingestion or gut passage involved. We present empirical evidence of synzoochoric mutualism between the hummingbird Sephanoides sephaniodes and cryptogams (one fern and seven moss species). Two species (Lophosoria quadripinnata and Ancistrodes genuflexa) constituted the bulk of nest biomass, and another six moss species were present in lesser quantity. The hummingbird was selective when collecting nest material so that the nests contained a higher density of reproductive structures (that could be dispersed further) than natural patches of the cryptogam species. Even after one year, the nests maintained half of the original reproductive structures (sporangia, sporophytes) and biomass, constituting an important dispersal source. These results show a new type of mutualism in which mosses could be dispersed throughout longer distances (several km) by hummingbirds and to higher positions (particularly for ground-living species, promoting dispersal potential). The hummingbird benefits from collecting cryptogam material for nest building, and cryptogams benefit from the concentration and relocation of diaspore sources into more effective recruiting sites. Similar mutualistic relationships could be a general phenomenon, of importance in many ecosystems.

  • 34.
    Pejler, Birgit
    Uppsala University, Disciplinary Domain of Science and Technology, Faculty of Mathematics and Science.
    Rotifer Plankton in Brackish and Freshwater Localities in Central Sweden1972In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 23, no 3, p. 416-419Article in journal (Refereed)
    Abstract [en]

    The rotifer plankton was studied in some freshwater and brackish water localities in easternmost Central Sweden. Concerning the general character and rotifer plankton, some of the lakes agreed with the type previously studied e.g. on the island of Gotland and designated as "oligotrophic - highly calcareous". Some of the lakes were recently separated from the sea, and in some others brackish water still intrudes at times. In such localities Synchaeta gyrina Hood was abundant. This rotifer evidently constitutes an edge species between brackish and fresh water. In the purely brackish localities, on the other hand, the species composition was similar to that found elsewhere in Baltic zooplankton.

  • 35.
    Persson, Jonas
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Limnology.
    Brett, Michael T.
    Vrede, Tobias
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Limnology.
    Ravet, Joseph L.
    Food quantity and quality regulation of trophic transfer between primary producers and a keystone grazer (Daphnia) in pelagic freshwater food webs2007In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 116, no 7, p. 1152-1163Article in journal (Refereed)
    Abstract [en]

    The transfer of energy and nutrients from plants to animals is a key process in all ecosystems. In lakes, inefficient transfer of primary producer derived energy can result in low animal growth rates, accumulation of nuisance phytoplankton blooms and dissipation of energy from the ecosystem. Most research on carbon transfer efficiency in pelagic food webs has focused on either food quantity or food quality, with the latter considered separately as either elemental stoichiometry or biochemical composition. The natural occurrence and magnitude of these types of growth limitations and their combined effects on Daphnia, a keystone grazer in pelagic freshwater ecosystems, are largely unknown. Our empirical models predict that the strength and nature of food quantity and quality limitation varies greatly with lake trophic state (total phosphorus, TP) and that Daphnia growth rates and thus energy and nutrient transfer efficiency are highest in lakes with intermediate trophic status (TP 10-25 μg l−1). We predict that food availability place the greatest constraint on Daphnia growth in nutrient poor lakes (TP≤4 μg l−1). Phosphorus limitation of Daphnia growth increased with decreasing TP, but the overall effect was never predicted to be the dominant constraining factor. Eicosapentaenoic acid (EPA, 20:5ω3) limitation was predicted to occur in both nutrient poor and nutrient rich lakes and placed the primary constraint on food quality in the most productive lakes. Two contrasting EPA-models gave different results on the magnitude of EPA-limitation, implying that additional food quality factors decrease Daphnia growth at high TP. In conclusion, the model predicts that Daphnia growth should peak in mesotrophic lakes, food quantity will place the greatest constraint on growth in oligotrophic lakes and EPA will primarily limit growth in eutrophic lakes.

  • 36. Rammul, Ü
    et al.
    Oksanen, T.
    Oksanen, L.
    Lehtelä, J.
    Virtanen, R.
    Olofsson, J.
    Strengbom, Joachim
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Ecological Botany.
    Rammul, I.
    Ericson, L.
    Vole-vegetation interactions in an experimental, enemy free taiga floor system2007In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 116, no 9, p. 1501-1513Article in journal (Refereed)
    Abstract [en]

    Vole–vegetation interactions in a predation-free taiga environment of northern Fennoscandia were studied by transferring vegetation from natural Microtus habitats into a greenhouse, where three habitat islands of about 30  m2 were created. The 'islands' were subjected to simulated summer conditions and a paired female field vole, Microtusagrestis, was introduced to each 'island'. The development of the female and her young was followed by recurrent live trapping. The development of the vegetation was followed by recurrent marking and censusing of plant shoots at intervals of five days. In the next growing season, two 'islands' were subjected to a new grazing treatment to study the impacts of repeated grazing on the vegetation and on the growth and reproduction of voles. Plant biomasses were harvested at the end of each trial. In all trials, the biomasses of graminoids and non-toxic herbs other than ferns, fireweeds and rosaceous plants were profoundly decimated. Even the biomass of a toxic herb Aconitum lycoctonum decreased largely at pace with the palatable herbs. The least preferred plant categories maintained their biomasses at control levels. Their neutral collective response was created by opposite species-level trends. Species typical for moist and nutrient-rich forests suffered from vole grazing, whereas the biomass of species adapted to disturbed habitats increased.

    In spite of the dramatic changes in the vegetation, the introduced female voles survived throughout the trials and reproduced normally. The young of their first litters survived well and reached the final weights typical for individuals starting to winter as immatures. We conclude that most of the plant biomass found on productive boreal forest floors is potential food for field voles and remains palatable for them even when subjected to recurrent, severe grazing. If nothing else than summer resources were limiting the growth of the field vole populations, the plants currently dominating moist and nutrient-rich taiga floors could not survive in this habitat.

  • 37.
    Scharnweber, Kristin
    et al.
    Leibniz-Inst. of Freshwater Ecology and Inland Fisheries.
    Vanni, M.J.
    Hilt, Sabine
    Syväranta, J
    Mehner, Thomas
    Boomerang ecosystem fluxes: organic carbon inputs from land to lakes are returned to terrestrial food webs via aquatic insects2014In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 123, no 12, p. 1439-1448Article in journal (Refereed)
    Abstract [en]

    Many ecosystems are linked to their adjacent ecosystems by movements of organisms. For instance, aquatic and terrestrial ecosystems are linked via emerging aquatic insects that serve as prey for terrestrial consumers. However, the role of these organisms in returning recycled carbon to the ecosystem from which it originated is not well known. This is due to the fact that values of carbon isotope signatures from terrestrial leaves and aquatic resources are usually similar and hence results of isotope mixing models need to be considered with caution. We overcame this problem by adding isotopically distinct terrestrial particulate organic carbon (tPOC) as a tracer to the experimental sides of two lakes that were divided in two equal halves with plastic curtains. We focused on aquatic insect larvae (Chironomidae) that fed on maize Zea mays leaves experimentally added to the lakes, and subsequently became prey for terrestrial predators (spiders) after emergence. The carbon isotope values of Chironomidae and spiders were significantly elevated in the lake treatment sides as compared to reference sides, whereas the values of all autochthonous resources were not affected by maize additions. Estimates from stable isotope mixing models indicated a low but demonstrable contribution of maize leaves to the diet of Chironomidae. Overlap between the isotope values of alder leaves, the major natural tPOC source, and autochthonous resources prevented a reliable quantification of allochthony of Chironomidae. However, we qualitatively demonstrated the flow of terrestrial particulate organic carbon to lakes, as leaf fall, and back to terrestrial surroundings via emerging insects. This ‘boomerang’ carbon flux between land and lakes blurs the distinction between autochthonous and allochthonous carbon sources.

  • 38.
    Sniegula, Szymon
    et al.
    Polish Acad Sci, Dept Ecosyst Conservat, Inst Nat Conservat, Al Mickiewicza 33, PL-31120 Krakow, Poland..
    Golab, Maria J.
    Polish Acad Sci, Dept Ecosyst Conservat, Inst Nat Conservat, Al Mickiewicza 33, PL-31120 Krakow, Poland..
    Johansson, Frank
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology.
    Time constraint effects on phenology and life history synchrony in a damselfly along a latitudinal gradient2016In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 125, no 3, p. 414-423Article in journal (Refereed)
    Abstract [en]

    In organisms with complex life cycles living in seasonal environments, the synchronisation of phenological events is important from the ecological and evolutionary perspectives. Life history transitions should be synchronised to a greater degree at northern latitudes. We quantified hatching and emergence timing and synchrony in the obligate univoltine damselfly Lestes sponsa along a latitudinal gradient covering its entire north-south range in Europe. In our first experiment, populations from different latitudes were grown in separate climate chambers simulating temperature and photoperiod conditions occurring at their sites of origin. Northern populations expressed early and high synchronous hatching and emergence, central populations intermediate, and southern populations late and low synchronous hatching and emergence. This pattern was expressed at both population and full-sibling family levels, indicating stronger selection for timing and synchronisation in the north compared to the south. In our second experiment, populations from all latitudes were reared in conditions simulating an average temperature and photoperiod over the latitudinal gradient. Interestingly, the pattern of timing and synchronisation was reversed with respect to latitude when compared to the pattern shown in the first experiment, indicating the importance of environmental factors in shaping phenological events. Our results indicate strong selection for timing and synchronisation of life history events at northern latitudes, caused by time constraints. Our results also show that it is important to use as natural conditions as possible in experiments on life history shifts in organisms with complex life cycles in order to achieve a correct understanding of these shifts.

  • 39.
    Snäll, Tord
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolutionary Biology.
    Ribeiro, P. J.
    Rydin, Håkan
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolutionary Biology.
    Spatial occurrence and colonisations in patch-tracking metapopulations: local conditions versus dispersal2003In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 103, no 3, p. 566-578Article in journal (Refereed)
    Abstract [en]

    We studied the relative importance of local variables and dispersal for the occurrence and colonisation of the epiphytic bryophytes Orthotricum speciosum (spore dispersed), and O. obtusifolium (spore and asexual gemmae) on aspen trees ('patches') in two forest landscapes (one old-growth and one fragmented) using multiple logistic regression. The relative importance of dispersal was quantified as the reduction of residual deviance for a connectivity variable. In modelling dispersal, we assumed that trees with low local abundance were recent colonisations, and that trees with high local abundance were diaspore sources for colonisation. The occurrence of O. speciosum in the fragmented landscape was most affected by shading, but also by connectivity, aspen diameter and vitality. In the old-growth landscape, connectivity was the single most important variable for recent colonisations, but its effect was lower than the sum of the effects of all local environmental variables. The occurrence of O. obtusifolium in the fragmented landscape was related to similar variables but the relative importance of these variables was different, and connectivity did not affect the probability of a recent colonisation in this species. We describe the epiphyte-tree system in the patch-tracking metapopulation model. In this model colonisations are distance dependent, but in contrast to the classical metapopulation model local extinctions are caused by deterministic patch destruction - once the epiphyte has colonised the tree it remains until the tree dies.

  • 40.
    Sundberg, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Animal Ecology.
    Parasites, plumage coloration and reproductive success in the yellowhammer, Emberiza citrinella1995In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 74, no 2, p. 331-339Article in journal (Refereed)
    Abstract [en]

    The prevalence and intensity of haematozoan parasites, with special emphasis on Haemoproteus coatneyi, was studied in relation to male plumage coloration, and reproductive success in a population of yellowhammers (Emberiza citrinella). Parasite prevalence and intensity were found to vary with time in season, emphasising the need to take samples during times of developed infection. Males were found with a peak intensity during the early breeding period and females slightly later, during the nestling period. The hypothesis of parasite-mediated sexual selection, according to which bright plumages have evolved in relation to degree of parasite infection, was tested. Male colour was found to reliably reveal the intensity of parasites during the breeding period. Males with high parasite intensity produced fewer fledglings. In spite of the negative correlation between parasite load and colour, males with more colour did not produce more offspring. No cost of parasites was found in females, and pairing was not assortative with respect to parasite infection. However, contrary to the hypothesis, no relationship between male colour and number of fledglings was found. Conclusively, some support was found for the hypothesis of parasite-mediated sexual selection, i.e. bright male plumages in the yellowhammer may thus have evolved or is maintained as a signal of level of parasite infection since a reduced reproductive success may be a cost imposed by high parasite load.

  • 41.
    Svanbäck, Richard
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Limnology.
    Eklöv, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Limnology.
    Morphology dependent foraging efficiency in perch: a trade-off for ecological specialization?2003In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 102, no 2, p. 273-284Article in journal (Refereed)
    Abstract [en]

    Trade-offs in foraging efficiency leading to divergent natural selection between and within populations exploiting different resources are thought to be a primary cause of trophic polymorphism. In this study we focused on the trade-offs in foraging efficiency and growth in a polymorphic perch population. Specifically, we related habitat-specific growth and diet of perch to perch morphology. In a subsequent laboratory study we experimentally tested the trade-off by testing the efficiency of perch with different morphology feeding on pelagic (Daphnia sp., Chaoborus sp.) and littoral (mayfly larvae) food resources. The feeding performance was tested in different physical environments to see if we could predict growth patterns in the field based on foraging rate and behavior of perch.

    In the field study, we found that the perch from the littoral and the pelagic zones differed in both morphology and diet. Within the littoral zone the deeper-bodied individuals grew faster compared to the more streamlined individuals, whereas the opposite pattern was found in the pelagic zone. In the aquarium experiments, perch from the littoral zone had higher capture rates on the pelagic prey types in vegetation trials and on mayfly larvae in both open water and vegetation trials. The pelagic perch had higher capture rates on the pelagic prey types in open water trials. The littoral perch had lower search velocity than the pelagic perch in open water trials whereas the opposite pattern was found in vegetation trials. The attack velocity of the pelagic perch was also higher than that of the littoral perch independent of vegetation structure. Our results suggest that there is a functional trade-off between performance in alternate habitats and general body form in perch. Such trade-offs may promote divergent natural selection and could be the mechanism that give rise to and upholds the pattern in the field.

  • 42.
    Svanbäck, Richard
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Limnology.
    Eklöv, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Limnology.
    Fransson, Rebecca
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Limnology.
    Holmgren, Kerstin
    Intra-specific competition drives multiple species trophic polymorphism in fish communities2008In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 117, no 1, p. 114-124Article in journal (Refereed)
    Abstract [en]

    It has been hypothesized that inter-specific competition will reduce species niche utilization and drive morphological evolution in character displacement. In the absence of a competitor, intra-specific competition may favor an expansion of the species niche and drive morphological evolution in character release. Despite of this theoretical framework, we sometimes find potential competitor species using the same niche range without any partitioning in niche. We used a database on test fishing in Sweden to evaluate the factors (inter- and intraspecific competition, predation, and abiotic factors) that could influence habitat choice of two competitor species. The pattern from the database shows that the occurrence of perch and roach occupying both littoral and pelagic habitats of lakes in Sweden is a general phenomenon. Furthermore, the results from the database suggest that this pattern is due to intra-specific competition rather than inter-specific competition or predation. In a field study, we estimated the morphological variation in perch and roach and found that, individuals of both species caught in the littoral zone were more deeper bodied compared to individuals caught in the pelagic zone. Pelagic perch fed more on zooplankton compared to littoral perch, independent of size, whereas the littoral perch had more macroinvertebrates and fish in their diet. Pelagic roach fed more on zooplankton compared to littoral roach, whereas littoral individuals fed more on plant material. Furthermore, we sampled littoral and pelagic fish from another lake to evaluate the generality of our first results and found the same habitat associated morphology in both perch and roach. The results show a consistent multi-species morphological separation in the littoral and pelagic habitats. This study suggests that intra-specific competition is possibly more important than inter-specific competition for the morphological pattern in the perch-roach system.

  • 43.
    Svanbäck, Richard
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Rydberg, Cecilia
    Leonardsson, Kjell
    Englund, Göran
    Diet specialization in a fluctuating population of Saduria entomon: a consequence of resource or forager densities?2011In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 120, no 6, p. 848-854Article in journal (Refereed)
    Abstract [en]

    Intraspecific competition has been shown to favor diet specialization among individuals. However, the question whether the competition takes the form of interference or exploitative in driving diet specialization has never been investigated. We investigated individual diet specialization in the isopod Saduria entomon, in relation to forager and resource biomasses in a system that exhibits predator-prey fluctuations in density. We found that individual diet specialization was only affected by the biomass of their preferred prey (Monoporeia affinis) and not by Saduria biomass; diet specialization was higher when Monoporeia biomass was low compared to when there were high Monoporeia biomass. Population diet breadth increased at low Monoporeia biomass whereas individual diet breadths were marginally affected by Monoporeia biomass. Overall, this led to the increase in diet specialization at low Monoporeia biomass. This study shows that predator-prey dynamics might influence diet specialization in the predator and that resource biomass, not forager biomass might be important for individual diet specialization.

  • 44. von Euler, Tove
    et al.
    Ågren, Jon
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Plant Ecology and Evolution.
    Ehrlen, Johan
    Floral display and habitat quality affect cost of reproduction in Primula farinosa2012In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 121, no 9, p. 1400-1407Article in journal (Refereed)
    Abstract [en]

    Costs of reproduction should depend on resource availability and on reproductive effort, which in turn may depend on traits influencing reproductive success. Therefore, variation in both habitat quality and reproductive traits should be considered when assessing reproductive costs. We investigated the effect of habitat quality and floral display on the costs of reproduction in the perennial herb Primula farinosa. In the study area, P. farinosa occurs in habitats that differ in water availability, which strongly influences plant performance. Furthermore, it displays a scape length dimorphism, with two distinct scape morphs differing in attractiveness to pollinators and reproductive success. To test the hypothesis that the cost of fruit production is higher in the long-scaped than in the short-scaped morph, and depends on water availability, we manipulated reproductive investment in eight P. farinosa populations along a gradient of soil moisture. Fruit set was higher in long-scaped individuals, and prevention of fruit set increased flower production in the following year among long-scaped, but not among short-scaped plants. Furthermore, costs of fruit production were evident at low and high moisture levels but not at intermediate levels. The results demonstrate an association between a genetically determined difference in floral display and cost of reproduction, and suggest that costs of reproduction are non-linearly related to water availability. They thus indicate links between the evolution of plant reproductive traits and plant life histories, and between habitat quality and optimal life history.

  • 45. Vrede, Tobias
    et al.
    Drakare, Stina
    Eklöv, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Hein, Arne
    Liess, Antonia
    Olsson, Jens
    Persson, Jonas
    Quevedo, Mario
    Stabo, Henrik Ragnarsson
    Svanbäck, Richard
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Ecological stoichiometry of Eurasian perch - intraspecific variation due to size, habitat and diet2011In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 120, no 6, p. 886-896Article in journal (Refereed)
    Abstract [en]

    The turnover and distribution of energy and nutrients in food webs is influenced by consumer stoichiometry. Although the stoichiometry of heterotrophs is generally considered to vary only little, there may be intraspecific variation due to factors such as habitat, resources, ontogeny and size. We examined intraspecific variation in Eurasian perch Perca fluviatilis stoichiometry, a common species that exhibits habitat and resource specialization, ontogenetic niche shifts and a large size range. This study investigated the elemental stoichiometry of a wide size range of perch from littoral and pelagic habitats. The mean C:N:P stoichiometry of whole perch was 37:9:1 (molar ratios). However, %C, %P, C:N, C:P and N:P varied with size, morphology, habitat and diet category. These factors together explained 24-40% of the variation in C:N:P stoichiometry. In contrast, perch stoichiometry was not related to diet stoichiometry, suggesting that the former is homeostatically regulated. The results suggest that the high P content of perch may result in stoichiometric constraints on the growth of non-piscivorous perch, and that piscivory is an efficient strategy for acquiring P. Resource polymorphism, individual diet specialization and intraspecific size variation are widespread among animals. Thus changes in stoichiometry with size, habitat, morphology and resource use, and therefore also stoichiometric demands, are probably common.

  • 46. Wiedermann, M. M.
    et al.
    Gunnarsson, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Ecological Botany.
    Nilsson, M. B.
    Nordin, A.
    Ericson, L.
    Can small-scale experiments predict ecosystem responses?: An example from peatlands2009In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 118, no 3, p. 449-457Article in journal (Refereed)
    Abstract [en]

    Oligotrophic, Sphagnum-dominated peatlands have been regarded as long-term stable ecosystems that function as carbon sinks. As a result of environmental perturbations, particularly anthropogenic N deposition, this view is now increasingly questioned. We examined whether small-scale field experiments can predict the direction and magnitude of ecosystem responses to increased N supply. We, therefore, compared data from a 10-year field experiment (involving deposition of 2, 15 and 30 kg N ha-1 year-1) with data from a gradient associated with increased N deposition (2, 8 and 12 kg N ha -1 year-1). We chose to compare: (1) the physiological response of Sphagnum balticum, measured in the form of N accumulation as free amino acids (NAA); and (2) changes in the total Sphagnum cover, the cover of S. balticum, and vascular plant cover. In all cases we found a highly significant correlation between the two data sets. We attribute the high correspondence between the two data sets to the key function of the dominant group of organisms, the Sphagna, that monopolize N availability and control the water balance, creating an environment hostile to vascular plants. Thus the key role of Sphagna as ecosystem engineers seems to supersede the role of other, scale-dependent processes. We also conclude that NAA is a sensitive indicator that can be used to signal the slow and gradual shift from Sphagnum to vascular plant dominance.

  • 47.
    Östman, Örjan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution.
    Chase, Jonathan M.
    Predator selectivity alters the effect of dispersal on coexistence among apparent competitors2007In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 116, no 3, p. 387-394Article in journal (Refereed)
    Abstract [en]

    While the majority of studies on dispersal effects on patterns of coexistence among species in a metacommunity have focused on resource competitors, dispersal in systems with predator-prey interactions may provide very different results. Here, we use an analytical model to study the effect of dispersal rates on coexistence of two prey species sharing a predator (apparent competition), when the traits of that predator vary. Specifically, we explore the range in immigration rates where apparent competitors are able to coexist, and how that range changes with predator selectivity and efficiency. We find that if the inferior apparent competitor has a higher probability of being consumed, it will require less immigration to invade and to exclude the superior prey as the predator becomes more opportunistic. However, if the inferior apparent competitor has a lower probability of being consumed (and lower growth rates), higher immigration is required for the inferior prey to invade and exclude the superior prey as the predator becomes more opportunistic. We further find that the largest range of immigration rates where prey coexist occurs when predator selectivity is intermediate (i.e. they do not show much bias towards consuming one species or the other). Increasing predator efficiency generally reduces the immigration rates necessary for the inferior apparent competitor to invade and exclude the superior apparent competitor, but also reduces the range of immigration rates where the two apparent competitors can coexist. However, when the superior apparent competitor has a higher probability of being consumed, increased predator efficiency can increase the range of parameters where the species can coexist. Our results are consistent with some of the variation observed in the effect of dispersal on prey species richness in empirical systems with top predators.

  • 48.
    Östman, Örjan
    et al.
    Department of Biology, Washington University, St. Louis, USA.
    Kneitel, Jamie M.
    Chase, Jonathan M.
    Disturbance alters habitat isolation's effect on biodiversity in aquatic microcosms2006In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 114, no 2, p. 360-366Article in journal (Refereed)
    Abstract [en]

    Isolated habitats generally have fewer species at local spatial scales than more connected habitats. However, over larger spatial scales, the response of species richness to variation in the degree of isolation is variable. Here, we hypothesized that the effects of habitat isolation on patterns of regional level species richness may depend at least in part on the level of disturbances those habitats receive. We tested this hypothesis in a microcosm experiment using an aquatic community consisting of container dwelling protists and rotifers by manipulating disturbance and dispersal to experimental regions factorially. In disturbed regions, regional species richness was lower in regions with isolated patches compared to regions where patches were experimentally connected by dispersal. A likely mechanism for this result is that dispersal from adjacent undisturbed local patches allowed disturbance-intolerant species a temporary refugia, thereby allowing regional coexistence of disturbance-tolerant and intolerant species. In contrast, without disturbances (and thus no temporal heterogeneity) it is likely that dispersal homogenized communities, leading to overall lower richness with higher dispersal. Our results emphasize the importance of simultaneously considering multiple limiting factors, disturbance and dispersal in this case, as well as the spatial scale of the response, in order to fully understand factors that control biodiversity.

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