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  • 201. Calboli, Federico C. F.
    et al.
    Byström, Pär
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Merila, Juha
    A test for within-lake niche differentiation in the nine-spined sticklebacks (Pungitius pungitius)2016In: Ecology and Evolution, ISSN 2045-7758, E-ISSN 2045-7758, Vol. 6, no 14, p. 4753-4760Article in journal (Refereed)
    Abstract [en]

    Specialization for the use of different resources can lead to ecological speciation. Accordingly, there are numerous examples of ecologically specialized pairs of fish species in postglacial lakes. Using a polymorphic panel of single nucleotide variants, we tested for genetic footprints of within-lake population stratification in nine-spined sticklebacks (Pungitius pungitius) collected from three habitats (viz. littoral, benthic, and pelagic) within a northern Swedish lake. Analyses of admixture, population structure, and relatedness all supported the conclusion that the fish from this lake form a single interbreeding unit.

  • 202. Callaghan, Terry V
    et al.
    Jonasson, Christer
    Thierfelder, Tomas
    Yang, Zhenlin
    Hedenas, Henrik
    Johansson, Margareta
    Molau, Ulf
    Van Bogaert, Rik
    Michelsen, Anders
    Olofsson, Johan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Gwynn-Jones, Dylan
    Bokhorst, Stef
    Phoenix, Gareth
    Bjerke, Jarle W
    Tommervik, Hans
    Christensen, Torben R
    Hanna, Edward
    Koller, Eva K
    Sloan, Victoria L
    Ecosystem change and stability over multiple decades in the Swedish subarctic: complex processes and multiple drivers2013In: Philosophical Transactions of the Royal Society of London. Biological Sciences, ISSN 0962-8436, E-ISSN 1471-2970, Vol. 368, no 1624Article in journal (Refereed)
    Abstract [en]

    The subarctic environment of northernmost Sweden has changed over the past century, particularly elements of climate and cryosphere. This paper presents a unique geo-referenced record of environmental and ecosystem observations from the area since 1913. Abiotic changes have been substantial. Vegetation changes include not only increases in growth and range extension but also counterintuitive decreases, and stability: all three possible responses. Changes in species composition within the major plant communities have ranged between almost no changes to almost a 50 per cent increase in the number of species. Changes in plant species abundance also vary with particularly large increases in trees and shrubs (up to 600%). There has been an increase in abundance of aspen and large changes in other plant communities responding to wetland area increases resulting from permafrost thaw. Populations of herbivores have responded to varying management practices and climate regimes, particularly changing snow conditions. While it is difficult to generalize and scale-up the site-specific changes in ecosystems, this very site-specificity, combined with projections of change, is of immediate relevance to local stakeholders who need to adapt to new opportunities and to respond to challenges. Furthermore, the relatively small area and its unique datasets are a microcosm of the complexity of Arctic landscapes in transition that remains to be documented.

  • 203.
    Cameron, Thomas C.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Univ Leeds, Inst Integrat & Comparat Biol, Ecol & Evolut Res Grp, Leeds LS2 9JT, W Yorkshire, England.
    O'Sullivan, Daniel
    Reynolds, Alan
    Piertney, Stuart B.
    Benton, Tim G.
    Eco-evolutionary dynamics in response to selection on life-history2013In: Ecology Letters, ISSN 1461-023X, E-ISSN 1461-0248, Vol. 16, no 6, p. 754-763Article in journal (Refereed)
    Abstract [en]

    Understanding the consequences of environmental change on ecological and evolutionary dynamics is inherently problematic because of the complex interplay between them. Using invertebrates in microcosms, we characterise phenotypic, population and evolutionary dynamics before, during and after exposure to a novel environment and harvesting over 20 generations. We demonstrate an evolved change in life-history traits (the age- and size-at-maturity, and survival to maturity) in response to selection caused by environmental change (wild to laboratory) and to harvesting (juvenile or adult). Life-history evolution, which drives changes in population growth rate and thus population dynamics, includes an increase in age-to-maturity of 76% (from 12.5 to 22days) in the unharvested populations as they adapt to the new environment. Evolutionary responses to harvesting are outweighed by the response to environmental change (similar to 1.4 vs. 4% change in age-at-maturity per generation). The adaptive response to environmental change converts a negative population growth trajectory into a positive one: an example of evolutionary rescue.

  • 204.
    Carlsson-Graner, Ulla
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Giles, Barbara
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Thrall, P. H.
    Centre for Plant Biodiversity Research, CSIRO - Plant Industry, GPO Box 1600, Canberra, ACT, 2601, Australia.
    Patterns of disease and host resistance in spatially structured systems2014In: European journal of plant pathology, ISSN 0929-1873, E-ISSN 1573-8469, Vol. 138, no 3, p. 499-511Article in journal (Refereed)
    Abstract [en]

    We use data from species of the anther-smut fungi and the host plants Lychnis alpina and Silene dioica to show that spatial structuring at different scales can influence patterns of disease and host resistance. Patterns of disease and host resistance were surveyed in an archipelago subject to land-uplift where populations of S. dioica constitute an age-structured metapopulation, and in three contrasting areas within the mainland range of L. alpina, where population distributions range from continuous, through patchy but spatially connected to highly isolated demes. In S. dioica, disease levels depend on the age, size and density of local patches and populations. Disease is most predictably found in larger dense host patches and populations of intermediate age, and more frequently goes extinct in small old populations. The rate of local disease spread is affected by the level of host resistance; S. dioica populations showing an increase in disease over time are more susceptible than populations where the disease has remained at low levels. Among-population variation in resistance is driven by founding events and populations remain differentiated due to limited gene flow between islands. As observed in the L. alpina system, when populations are more connected, a greater fraction of populations have disease present. Results from a simulation model argue that, while increased dispersal in connected systems can increase disease spread, it may also favour selection of host resistance which ultimately reduces disease levels within populations. This could explain the observed lower disease prevalence in L. alpina in regions where populations are more continuous.

  • 205. Carr, J. A.
    et al.
    Seekell, David A.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    D'Odorico, P.
    Inequality or injustice in water use for food?2015In: Environmental Research Letters, ISSN 1748-9326, E-ISSN 1748-9326, Vol. 10, no 2, article id 024013Article in journal (Refereed)
    Abstract [en]

    The global distributions of water availability and population density are uneven and therefore inequality exists in human access to freshwater resources. Is this inequality unjust or only regrettable? To examine this question we formulated and evaluated elementary principles of water ethics relative to human rights for water, and the need for global trade to improve societal access to water by transferring 'virtual water' embedded in plant and animal commodities. We defined human welfare benchmarks and evaluated patterns of water use with and without trade over a 25-year period to identify the influence of trade and inequality on equitability of water use. We found that trade improves mean water use and wellbeing, relative to human welfare benchmarks, suggesting that inequality is regrettable but not necessarily unjust. However, trade has not significantly contributed to redressing inequality. Hence, directed trade decisions can improve future conditions of water and food scarcity through reduced inequality.

  • 206. Carr, Joel A.
    et al.
    D'Odorico, Paolo
    Suweis, Samir
    Seekell, David A.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    What commodities and countries impact inequality in the global food system?2016In: Environmental Research Letters, ISSN 1748-9326, E-ISSN 1748-9326, Vol. 11, no 9, article id 095013Article in journal (Refereed)
    Abstract [en]

    The global distribution of food production is unequal relative to the distribution of human populations. International trade can increase or decrease inequality in food availability, but little is known about how specific countries and commodities contribute to this redistribution. We present a method based on the Gini coefficient for evaluating the contributions of country and commodity specific trade to inequality in the global food system. We applied the method to global food production and trade data for the years 1986-2011 to identify the specific countries and commodities that contribute to increasing and decreasing inequality in global food availability relative to food production. Overall, international trade reduced inequality in food availability by 25%-33% relative to the distribution of food production, depending on the year. Across all years, about 58% of the total trade links acted to reduce inequality with similar to 4% of the links providing 95% of the reduction in inequality. Exports from United States of America, Malaysia, Argentina, and Canada are particularly important in decreasing inequality. Specific commodities that reduce inequality when traded include cereals and vegetables. Some trade connections contribute to increasing inequality, but this effect is mostly concentrated within a small number of commodities including fruits, stimulants, and nuts. In terms of specific countries, exports from Slovenia, Oman, Singapore, and Germany act to increase overall inequality. Collectively, our analysis and results represent an opportunity for building an enhanced understanding of global-scale patterns in food availability.

  • 207. Catalan, Jordi
    et al.
    Pla-Rabes, Sergi
    Wolfe, Alexander P.
    Smol, John P.
    Ruehland, Kathleen M.
    Anderson, N. John
    Kopacek, Jiri
    Stuchlik, Evzen
    Schmidt, Roland
    Koinig, Karin A.
    Camarero, Lluis
    Flower, Roger J.
    Heiri, Oliver
    Kamenik, Christian
    Korhola, Atte
    Leavitt, Peter R.
    Psenner, Roland
    Renberg, Ingemar
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Global change revealed by palaeolimnological records from remote lakes: a review2013In: Journal of Paleolimnology, ISSN 0921-2728, E-ISSN 1573-0417, Vol. 49, no 3, p. 513-535Article in journal (Refereed)
    Abstract [en]

    Over recent decades, palaeolimnological records from remote sites have provided convincing evidence for the onset and development of several facets of global environmental change. Remote lakes, defined here as those occurring in high latitude or high altitude regions, have the advantage of not being overprinted by local anthropogenic processes. As such, many of these sites record broad-scale environmental changes, frequently driven by regime shifts in the Earth system. Here, we review a selection of studies from North America and Europe and discuss their broader implications. The history of investigation has evolved synchronously with the scope and awareness of environmental problems. An initial focus on acid deposition switched to metal and other types of pollutants, then climate change and eventually to atmospheric deposition-fertilising effects. However, none of these topics is independent of the other, and all of them affect ecosystem function and biodiversity in profound ways. Currently, remote lake palaeolimnology is developing unique datasets for each region investigated that benchmark current trends with respect to past, purely natural variability in lake systems. Fostering conceptual and methodological bridges with other environmental disciplines will upturn contribution of remote lake palaeolimnology in solving existing and emerging questions in global change science and planetary stewardship.

  • 208.
    Catford, Jane A.
    et al.
    Department of Resource Management and Geography, The University of Melbourne, Australia.
    Jansson, Roland
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Reducing redundancy in invasion ecology by integrating hypotheses into a single theoretical framework2009In: Diversity & distributions: A journal of biological invasions and biodiversity, ISSN 1366-9516, E-ISSN 1472-4642, Vol. 15, no 1, p. 22-40Article in journal (Refereed)
    Abstract [en]

    Aim: Invasion ecology includes many hypotheses. Empirical evidence suggests that most of these can explain the success of some invaders to some degree in some circumstances. If they all are correct, what does this tell us about invasion? We illustrate the major themes in invasion ecology, and provide an overarching framework that helps organize research and foster links among subfields of invasion ecology and ecology more generally.

    Location: Global.

    Methods: We review and synthesize 29 leading hypotheses in plant invasion ecology. Structured around propagule pressure (P), abiotic characteristics (A) and biotic characteristics (B), with the additional influence of humans (H) on P, A and B (hereon PAB), we show how these hypotheses fit into one paradigm. P is based on the size and frequency of introductions, A incorporates ecosystem invasibility based on physical conditions, and B includes the characteristics of invading species (invasiveness), the recipient community and their interactions. Having justified the PAB framework, we propose a way in which invasion research could progress.

    Results: By highlighting the common ground among hypotheses, we show that invasion ecology is encumbered by theoretical redundancy that can be removed through integration. Using both holistic and incremental approaches, we show how the PAB framework can guide research and quantify the relative importance of different invasion mechanisms.

    Main conclusions: If the prime aim is to identify the main cause of invasion success, we contend that a top-down approach that focuses on PAB maximizes research efficiency. This approach identifies the most influential factors first, and subsequently narrows the number of potential causal mechanisms. By viewing invasion as a multifaceted process that can be partitioned into major drivers and broken down into a series of sequential steps, invasion theory can be rigorously tested, understanding improved and effective weed management techniques identified.

  • 209. Chase, J. M.
    et al.
    Abrams, P. A.
    Grover, J. P.
    Diehl, S.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Chesson, P.
    Holt, R. D.
    Richards, S. A.
    Nisbet, R. M.
    Case, T. J.
    The interaction between predation and competition: a review and synthesis2002In: Ecology Letters, Vol. 5, no 2, p. 302-315Article in journal (Refereed)
    Abstract [en]

    This review discusses the interface between two of the most important types of interactions between species, interspecific competition and predation. Predation has been claimed to increase, decrease, or have little effect on, the strength, impact or importance of interspecific competition. There is confusion about both the meaning these terms and the likelihood of, and conditions required for, each of these outcomes. In this article we distinguish among three measures of the influence of predation on competitive outcomes: short-term per capita consumption or growth rates, long-term changes in density and the probability of competitive coexistence. We then outline various theoretical mechanisms that can lead to qualitatively, distinct effects. of predators,. The qualitative effect of predators can depend both on the mechanism of competition and on the definition of competitive strength/impact. In assessing the empirical literature, we ask: (1) What definitions of competitive strength/impact have been assumed? (2) Does strong evidence exist to support one or more of the possible mechanisms that can produce a given outcome? (3) Do biases in the choice of organism or manipulation exist, and are they, likely, to have influenced the conclusions reached? We conclude by discussing several unanswered questions, and espouse a stronger interchange between empirical and theoretical approaches to this important question.

  • 210.
    Cherif, Mehdi
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Stoichiometry and Population Growth in Osmotrophs and Non‐Osmotrophs2016In: eLS, John Wiley & Sons, 2016, p. 1-6Chapter in book (Refereed)
    Abstract [en]

    Growth is a process fundamental to life. It implies an increase in not only energy and information but also matter content. Recent advances in ecology have demonstrated that the elemental composition of organisms – their stoichiometry – is inextricably linked to their growth rate. Unbalances between the demands of elements for growth and their relative availabilities often result in elemental limitation. Also, different cellular components have different elemental compositions, and thus changes in allocation between uptake and assembly machineries affect both growth rate and elemental composition at the organismal level. Osmotrophs (including autotrophs) acquire essential elements through a vast set of separate molecules, resulting in more flexible stoichiometries compared to non-osmotrophs that ingest their preys in one package. Relationships between elemental composition and growth rate should be considered differently for individuals and for populations, as processes and mechanisms differ between the two scales, and more generally among the various biological scales.

  • 211.
    Cherif, Mehdi
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Elser, James
    Ecological Stoichiometry2016In: Oxford Bibliographies in Ecology, Oxford Bibliographies, 2016Chapter in book (Refereed)
    Abstract [en]

    Ecological stoichiometry (ES) is the study of the balance of energy and multiple chemical elements in ecological interactions. Although much of the foundation of this field lies in studies of lakes (and especially of lake plankton), the application of ES has greatly expanded in 21st century, with extensions to streams, soils, grasslands, forests, and other ecosystems. This article provides a guide to recent introductory articles and reviews of the ES approach, to some of the foundational papers that preceded the formal definition of ES, and to a cross-section of papers dealing with biochemical, evolutionary, and ecological (especially biogeochemical) applications of ES. The field remains highly dynamic: a topic search on “ecolog stoichiometry” in ISI Web of Science yields more than 6,100 citations per year (in 2013; compared to less than five hundred in 1993). Thus, this annotated bibliography can only touch on the tip of this growing iceberg.

  • 212.
    Cherif, Mehdi
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Faithfull, Carolyn
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Guo, Junwen
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Meunier, Cédric L.
    Alfred-Wegener-Institut, Helmholtz-Zentrum für Poslar- und Meeresforschung, Biologische Anstalt Helgoland, Helgoland, Germany.
    Sitters, Judith
    Ecology and Biodiversity, Department Biology, Vrije Universiteit Brussel, Brussels, Belgium.
    Uszko, Wojciech
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Rivera Vasconcelos, Francisco
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    An operational framework for the advancement of a molecule-to-biosphere stoichiometry theory2017In: Frontiers in Marine Science, E-ISSN 2296-7745, Vol. 4, article id 286Article in journal (Refereed)
    Abstract [en]

    Biological stoichiometry is an approach that focuses on the balance of elements in biological interactions. It is a theory that has the potential to causally link material processes at all biological levels—from molecules to the biosphere. But the lack of a coherent operational framework has so far restricted progress in this direction. Here, we provide a framework to help infer how a stoichiometric imbalance observed at one level impacts all other biological levels. Our framework enables us to highlight the areas of the theory in need of completion, development and integration at all biological levels. Our hope is that this framework will contribute to the building of a more predictive theory of elemental transfers within the biosphere, and thus, to a better understanding of human-induced perturbations to the global biogeochemical cycles.

  • 213.
    Cherif, Mehdi
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Granados, Monica
    Duffy, Sean
    Robert, Pauline
    Pequin, Berangere
    Mohit, Vani
    McKindsey, Christopher W.
    Archambault, Philippe
    Myrand, Bruno
    Lovejoy, Connie
    Tremblay, Rejean
    Plourde, Stephane
    Fussmann, Gregor F.
    Potential for Local Fertilization: A Benthocosm Test of Long-Term and Short-Term Effects of Mussel Excretion on the Plankton2016In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 11, no 6, article id e0156411Article in journal (Refereed)
    Abstract [en]

    Mussel aquaculture has expanded worldwide and it is important to assess its impact on the water column and the planktonic food web to determine the sustainability of farming practices. Mussel farming may affect the planktonic food web indirectly by excreting bioavailable nutrients in the water column (a short-term effect) or by increasing nutrient effluxes from bio-deposit-enriched sediments (a long-term effect). We tested both of these indirect effects in a lagoon by using plankton-enclosing benthocosms that were placed on the bottom of a shallow lagoon either inside of a mussel farm or at reference sites with no history of aquaculture. At each site, half of the benthocosms were enriched with seawater that had held mussels (excretion treatment), the other half received non-enriched seawater as a control treatment. We monitored nutrients ([PO43-] and [NH4+]), dissolved oxygen and plankton components (bacteria, the phytoplankton and the zooplankton) over 5 days. We found a significant relationship between long-term accumulation of mussel biodeposits in sediments, water-column nutrient concentrations and plankton growth. Effects of mussel excretion were not detected, too weak to be significant given the spatial and temporal variability observed in the lagoon. Effects of mussels on the water column are thus likely to be coupled to benthic processes in such semi-enclosed water bodies.

  • 214.
    Cherif, Mehdi
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Loreau, Michel
    Plant - herbivore -decomposer stoichiometric mismatches and nutrientcycling in ecosystems2013In: Proceedings of the Royal Society of London. Biological Sciences, ISSN 0962-8452, E-ISSN 1471-2954, Vol. 280, no 1754, p. 20122453-Article in journal (Refereed)
    Abstract [en]

    Plant stoichiometry is thought to have a major influence on how herbivores affect nutrient availability in ecosystems. Most conceptual models predict that plants with high nutrient contents increase nutrient excretion by herbivores, in turn raising nutrient availability. To test this hypothesis, we built a stoichiometrically explicit model that includes a simple but thorough description of the processes of herbivory and decomposition. Our results challenge traditional views of herbivore impacts on nutrient availability in many ways. They show that the relationship between plant nutrient content and the impact of herbivores predicted by conceptual models holds only at high plant nutrient contents. At low plant nutrient contents, the impact of herbivores is mediated by the mineralization/immobilization of nutrients by decomposers and by the type of resource limiting the growth of decomposers. Both parameters are functions of the mismatch between plant and decomposer stoichiometries. Our work provides new predictions about the impacts of herbivores on ecosystemfertility that depend on critical interactions between plant, herbivore and decomposer stoichiometries in ecosystems.

  • 215.
    Cherif, Mehdi
    et al.
    Biogéochimie et Ecologie des Milieux Continentaux Laboratory, Unité Mixte de Recherche 7618, Ecole Normale Supérieure.
    Loreau, Michel
    Department of Biology, McGill University.
    Stoichiometric constraints on resource use, competitive interactions, and elemental cycling in microbial decomposers2007In: American Naturalist, ISSN 0003-0147, E-ISSN 1537-5323, Vol. 169, no 6, p. 709-724Article in journal (Refereed)
    Abstract [en]

    Heterotrophic microbial decomposers, such as bacteria and fungi, immobilize or mineralize inorganic elements, depending on their elemental composition and that of their organic resource. This fact has major implications for their interactions with other consumers of inorganic elements. We combine the stoichiometric and resource-ratio approaches in a model describing the use by decomposers of an organic and an inorganic resource containing the same essential element, to study its consequences on decomposer interactions and their role in elemental cycling. Our model considers the elemental composition of organic matter and the principle of its homeostasis explicitly. New predictions emerge, in particular, ( 1) stoichiometric constraints generate a trade-off between the R* values of decomposers for the two resources; ( 2) they create favorable conditions for the coexistence of decomposers limited by different resources and with different elemental demands; ( 3) however, combined with conditions on species-specific equilibrium limitation, they draw decomposers toward colimitation by the organic and inorganic resources on an evolutionary time scale. Moreover, we derive the conditions under which decomposers switch from consumption to excretion of the inorganic resource. We expect our predictions to be useful in explaining the community structure of decomposers and their interactions with other consumers of inorganic resources, particularly primary producers.

  • 216.
    Cherif, Mehdi
    et al.
    Department of Biology, McGill University.
    Loreau, Michel
    Department of Biology, McGill University.
    Towards a more biologically realistic use of Droop's equations to model growth under multiple nutrient limitation2010In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 119, no 6, p. 897-907Article in journal (Refereed)
    Abstract [en]

    Droop's model was originally designed to describe the growth of unicellular phytoplankton species in chemostats but it is now commonly used for a variety of organisms in models of trophic interactions, ecosystem functioning, and evolution. Despite its ubiquitous use, Droop's model is still limited by several simplifying assumptions. For example, the assumption of equal theoretical maximum growth rates for all nutrients is commonly used to describe growth limited by multiple nutrients. This assumption, however, is both biologically unrealistic and potentially misleading. We propose the alternative hypothesis of equal realized maximum growth rates for all nutrients. We support our hypothesis with empirical and theoretical arguments and discuss how it may improve our understanding of the biology of growth, while avoiding some of the pitfalls of the previous assumption.

  • 217.
    Cherif, Mehdi
    et al.
    Department of Biology, McGill University.
    Loreau, Michel
    Department of Biology, McGill University.
    When microbes and consumers determine the limiting nutrient of autotrophs: a theoretical analysis2009In: Proceedings of the Royal Society of London. Biological Sciences, ISSN 0962-8452, E-ISSN 1471-2954, Vol. 276, no 1656, p. 487-497Article in journal (Refereed)
    Abstract [en]

    Ecological stoichiometry postulates that differential nutrient recycling of elements such as nitrogen and phosphorus by consumers can shift the element that limits plant growth. However, this hypothesis has so far considered the effect of consumers, mostly herbivores, out of their food-web context. Microbial decomposers are important components of food webs, and might prove as important as consumers in changing the availability of elements for plants. In this theoretical study, we investigate how decomposers determine the nutrient that limits plants, both by feeding on nutrients and organic carbon released by plants and consumers, and by being fed upon by omnivorous consumers. We show that decomposers can greatly alter the relative availability of nutrients for plants. The type of limiting nutrient promoted by decomposers depends on their own elemental composition and, when applicable, on their ingestion by consumers. Our results highlight the limitations of previous stoichiometric theories of plant nutrient limitation control, which often ignored trophic levels other than plants and herbivores. They also suggest that detrital chains play an important role in determining plant nutrient limitation in many ecosystems.

  • 218.
    Chintapalli, Bahdri
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Edibility of bacteria isolated ice, water column and sediment in a brackish sea area.2006Independent thesis Advanced level (degree of Master (One Year)), 20 credits / 30 HE creditsStudent thesis
  • 219.
    Christensen, Pernilla
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    The long-term decline of the grey-sided vole (Clethrionomys rufocanus) in boreal Sweden: importance of focal forest patch and matrix2006Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    There has been a long-term decline in number of cyclic vole populations in boreal Sweden since the 1970s. Several hypotheses have been suggested to explain this decline. Commonly for C. glareolus, C. rufocanus and M. agrestis, the decline has followed upon an increased frequency and severeness of winter declines and has shown up as a drop in spring densities. The spring decline is most pronounced for C. rufocanus. In contrast to other voles, C. rufocanus also show a decline in fall densities, suggesting some additional disturbance in this species. Habitat fragmentation has been suggested as such an additional disturbance and in this thesis the effect of habitat fragmentation on C. rufocanus is explored.

    At first the sampling method was evaluated i.e. whether the decline could be due to destructive sampling when the method in use in the long-term monitoring is snap-trapping. This resulted in a rejection of the destructive sampling hypothesis as a possible cause behind the decline in C. rufocanus. Habitat preference revealed that three habitats at the local scale (trap station) were high quality habitats for C. rufocanus: forest of moist and wet/hydric dwarf-shrub type, in addition to forest/swamp complexes rich in dwarf-shrubs. The occurrence of C. rufocanus at the landscape scale was positively correlated with the amount of boulder fields and a low degree of fragmentation of old-growth pine forests. There was considerable local variation in the decline in vole density among the 58 1-ha sampling plots, with respect to both density and timing of the decline, which suggested that habitat destruction outside sampling plots might be involved. Overall, clear-cuts had a negative influence on vole densities at both the local and landscape scale. A multiple regression analysis suggested that having both a high quality habitat at the local scale and a high proximity among xeric-mesic mires and a low connectivity among clear-cuts at the landscape scale were important for the occurrence of C. rufocanus.

    Initial analysis at the landscape scale were based on landscape data collected from 2.5 x 2.5 km areas centred on the individual vole sampling plots. Further investigations, however, on the patch level suggest that focal forest patch size and quality was of major importance in determining occurrence and persistence of C. rufocanus. Although not tested formally in these studies, the habitat fragmentation hypothesis has so far received support. Currently C. rufocanus seems to be affected negatively by too low patch sizes of suitable habitats in the surrounding landscape suggesting that the amount of suitable habitats could already be below the fragmentation threshold. However, this has to be evaluated further. Work is in progress to establish time-series over local landscape changes, and to evaluate if such changes have been associated with local declines of C. rufocanus and whether habitat loss, true habitat fragmentation or both have been influential.

  • 220. Claessen, David
    et al.
    Andersson, Jens
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Persson, Lennart
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    de Roos, André M
    The effect of population size and recombination on delayed evolution of polymorphism and speciation in sexual populations2008In: American Naturalist, ISSN 0003-0147, E-ISSN 1537-5323, Vol. 172, no 1, p. E18-34Article in journal (Refereed)
    Abstract [en]

    Recent theory suggests that absolute population size may qualitatively influence the outcome of evolution under disruptive selection in asexual populations. Large populations are predicted to undergo rapid evolutionary branching; however, in small populations, the waiting time to branching increases steeply with decreasing abundance, and below a critical size, the population remains monomorphic indefinitely. Here, we (1) extend the theory to sexual populations and (2) confront its predictions with empirical data, testing statistically whether lake size affects the level of resource polymorphism in arctic char (Salvelinus alpinus) in 22 lakes of different sizes. For a given level of recombination, our model predicts qualitatively similar relations between population size and time to evolutionary branching (either speciation or evolution of genetic polymorphism) as the asexual model, while recombination further increases the delay to branching. The loss of polymorphism at certain loci, an inherent aspect of multilocus-trait evolution, may increase the delay to speciation, resulting in stable genetic polymorphism without speciation. The empirical analysis demonstrates that the occurrence of resource polymorphism depends on both lake size and the number of coexisting fish species. For a given number of coexisting species, the level of polymorphism increases significantly with lake size, thus confirming our model prediction.

  • 221. Classen, Aimee T.
    et al.
    Sundqvist, Maja K.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Henning, Jeremiah A.
    Newman, Gregory S.
    Moore, Jessica A. M.
    Cregger, Melissa A.
    Moorhead, Leigh C.
    Patterson, Courtney M.
    Direct and indirect effects of climate change on soil microbial and soil microbial-plant interactions: What lies ahead?2015In: Ecosphere, ISSN 2150-8925, E-ISSN 2150-8925, Vol. 6, no 8, article id 130Article in journal (Refereed)
    Abstract [en]

    Global change is altering species distributions and thus interactions among organisms. Organisms live in concert with thousands of other species, some beneficial, some pathogenic, some which have little to no effect in complex communities. Since natural communities are composed of organisms with very different life history traits and dispersal ability it is unlikely they will all respond to climatic change in a similar way. Disjuncts in plant-pollinator and plant-herbivore interactions under global change have been relatively well described, but plant-soil microorganism and soil microbe-microbe relationships have received less attention. Since soil microorganisms regulate nutrient transformations, provide plants with nutrients, allow co-existence among neighbors, and control plant populations, changes in soil microorganism-plant interactions could have significant ramifications for plant community composition and ecosystem function. In this paper we explore how climatic change affects soil microbes and soil microbe-plant interactions directly and indirectly, discuss what we see as emerging and exciting questions and areas for future research, and discuss what ramifications changes in these interactions may have on the composition and function of ecosystems.

  • 222. Codling, Garry
    et al.
    Halsall, Crispin
    Ahrens, Lutz
    Del Vento, Sabino
    Wiberg, Karin
    Bergknut, Magnus
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Laudon, Hjalmar
    Ebinghaus, Ralf
    The fate of per- and polyfluoroalkyl substances within a melting snowpack of a boreal forest2014In: Environmental Pollution, ISSN 0269-7491, E-ISSN 1873-6424, Vol. 191, p. 190-198Article in journal (Refereed)
    Abstract [en]

    Per- and polyfluoroallcyl substances (PFAS) were measured systematically in a snowpack in northern Sweden to determine chemical behaviour during seasonal melt. Average PFAS concentrations were generally low, but displayed a wide range with median (range) concentrations of PFOA and PFOS of 66.5 pg L-1 (ND-122) and 20.5 pg L-1 (2.60-253) respectively. Average concentrations of the shorter chain, C4 and C5 perfluoroalkyl carboxylates (PFCAs) and perfluoroalkyl sulfonates (PFSAs), were similar to 10-fold higher. Differences in the PFAS concentrations and profile were observed between surface snow and deeper layers, with evidence of PFAS migration to deeper snow layers as melt progressed. Chemical loads (ng m(-2)) for C4-9 PFCAs decreased gradually as melt progressed, but increased for C-4, C6-8 PFSAs and the longer chain C10-12 PFCAs. This enrichment in the diminishing snowpack is an unusual phenomenon that will affect PFAS elution with meltwater and subsequent entry to catchment surface waters. (C) 2014 Elsevier Ltd. All rights reserved.

  • 223. Collis, Ken
    et al.
    Roby, Daniel D.
    Larson, Keith W.
    Department of Fisheries and Wildlife, 104 Nash Hall, Oregon State University, Corvallis, OR, 97331, USA; Evolutionary Ecology, Lund University, Sølvegatan 37, 223 62 Lund, Sweden.
    Adrean, Lindsay J.
    Nelson, S. Kim
    Evans, Allen F.
    Hostetter, Nathan
    Battaglia, Dan
    Lyons, Donald E.
    Marcella, Tim
    Patterson, Allison
    Trends in Caspian Tern Nesting and Diet in San Francisco Bay: Conservation Implications for Terns and Salmonids2012In: Waterbirds (De Leon Springs, Fla.), ISSN 1524-4695, E-ISSN 1938-5390, Vol. 35, no 1, p. 25-34Article in journal (Refereed)
    Abstract [en]

    Colony size, nesting ecology and diet of Caspian Terns (Hydroprogne caspia) were investigated in the San Francisco Bay area (SFBA) during 2003-2009 to assess the potential for conservation of the tern breeding population and possible negative effects of predation on survival of juvenile salmonids (Oncorhyn-chusspp.). Numbers of breeding Caspian Terns declined 36% from 2003 to 2009, mostly due to abandonment of the Knight Island colony and decline of the Brooks Island colony, the two largest colonies in the SFBA. Concurrently, nesting success declined 69% associated with colony site characteristics such as (a) quality and quantity of nesting substrate, (b) vulnerability to nest predators, (c) displacement by other colonial waterbirds and (d) human disturbance. Marine fishes were the predominant prey in tern diets from the SFBA; however, diet composition varied among colonies. Juvenile salmonids comprised 22.9% of the diet of terns nesting in the North Bay, 5.3% of diet of terns nesting in the Central Bay, and 0.1% in the South Bay. Construction or restoration of nesting islands in the South Bay may help maintain and restore breeding Caspian Terns without enhancing mortality of salmonid stocks of conservation concern.

  • 224. Cooper, S. D.
    et al.
    Barmuta, L.
    Sarnelle, O.
    Kratz, K.
    Diehl, S.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Quantifying spatial heterogeneity in streams1997In: Journal of the North American Benthological Society, Vol. 16, no 1, p. 174-188Article in journal (Refereed)
    Abstract [en]

    Although theoretical and empirical studies show that spatial heterogeneity has important effects on the dynamics of populations and the structure of communities, there has been little rigorous quantification of terms like ''patchiness'' or ''spatial heterogeneity'' in studies of lotic systems. In order to compare the spatial heterogeneity of different systems and understand the causes and consequences of that heterogeneity, we must first be able to quantitatively measure it. Spatial heterogeneity has many aspects that change with the scale of our observations, so we need a battery of descriptive measures that explicitly consider the scale-dependence of ecological pattern Response variables exhibiting similar frequency distributions (i.e., similar overall variability) can have very different spatial distributions; consequently, descriptions of spatial heterogeneity require spatial data, i.e., data related to geographic locations (maps). We review statistical techniques for quantitatively describing aspects of heterogeneity in spatial data, emphasizing the decomposition of heterogeneity into different scales of variation (trends, overall variability and spatial dependence or autocorrelation). Gradients in spatial data can be evaluated using trend analyses (e.g., regressions), whereas the spatial structure of variation around trends can be evaluated using geostatistical methods. The central concept of geostatistics is spatial dependence, which is the degree to which values of a response variable differ as a function of the distance (lag) between sampling locations. Semivariograms plot variation among samples separated by a common lag Versus lag, and can be objectively decomposed by piece-wise regression techniques to estimate the strength and scales of spatial dependence. A variety of other methods can be used to quantify spatial heterogeneity from categorical and numerical maps depending on the question of interest and the underlying structure of the spatial data (e.g., methods derived from fractal geometry and information theory, nearest neighbor analysis, spectral analysis, Mantel's test). Spatial heterogeneity in stream organisms is driven by local variation in environmental conditions, by interactions between individuals of the same or different species, and by the effects of organisms on their abiotic environment. By applying geostatistical methods to spatial data collected from field experiments, stream ecologists can evaluate the effects of biotic and abiotic factors on the spatial arrangement of organisms in streams. We present examples of data obtained from experiments examining how consumers affect, and respond to, spatial heterogeneity in their resources. The results indicate that consumer-resource feedbacks should be considered when modeling the causes and consequences of spatial heterogeneity in streams.

  • 225. Cote, Julien
    et al.
    Brodin, Tomas
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Fogarty, Sean
    Sih, Andrew
    Non-random dispersal mediates invader impacts on the invertebrate community2017In: Journal of Animal Ecology, ISSN 0021-8790, E-ISSN 1365-2656, Vol. 86, no 6, p. 1298-1307Article in journal (Refereed)
    Abstract [en]

    Dispersers are often not a random draw from a population, dispersal propensity being conditional on individual phenotypic traits and local contexts. This non-randomness consequently results in phenotypic differences between dispersers and non-dispersers and, in the context of biological invasions, in an invasion front made of individuals with a biased phenotype. This bias of phenotypes at the front may subsequently modulate the strength of ecological effects of an invasive species on invaded communities. We recently demonstrated that more asocial mosquitofish (Gambusia affinis), one of the 100 worst invasive species, disperse further, suggesting a sociability-biased invasion front. As behavioural types are related to the strength of interspecific interactions, an invasion by a biased subset of individuals should have important ecological implications for native communities. Here, we tested the impact of phenotypic biases in dispersing individuals (relative to non-dispersers) on prey communities in experimental mesocosms. We show that dispersers reduce prey abundance more than do non-dispersers during the first 4 weeks after introduction, and that the disperser's social types are likely drivers of these differences. These differences in prey communities disappeared after 8 weeks suggesting prey community resilience against predation in these mesocosm ecosystems. Consequently, we call for the integration of non-random dispersal, dispersal syndromes and more generally intraspecific variation into studies predicting the impacts of invasions.

  • 226. Cote, Julien
    et al.
    Fogarty, Sean
    Tymen, Blaise
    Sih, Andrew
    Brodin, Tomas
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Personality-dependent dispersal cancelled under predation risk2013In: Proceedings of the Royal Society of London. Biological Sciences, ISSN 0962-8452, E-ISSN 1471-2954, Vol. 280, no 1773, p. 20132349-Article in journal (Refereed)
    Abstract [en]

    Dispersal is a fundamental life-history trait for many ecological processes. Recent studies suggest that dispersers, in comparison to residents, display various phenotypic specializations increasing their dispersal inclination or success. Among them, dispersers are believed to be consistently more bold, exploratory, asocial or aggressive than residents. These links between behavioural types and dispersal should vary with the cause of dispersal. However, with the exception of one study, personality-dependent dispersal has not been studied in contrasting environments. Here, we used mosquitofish (Gambusia affinis) to test whether personality-dependent dispersal varies with predation risk, a factor that should induce boldness or sociability-dependent dispersal. Corroborating previous studies, we found that dispersing mosquitofish are less social than non-dispersing fish when there was no predation risk. However, personality-dependent dispersal is negated under predation risk, dispersers having similar personality types to residents. Our results suggest that adaptive dispersal decisions could commonly depend on interactions between phenotypes and ecological contexts.

  • 227. Craig, David P.
    et al.
    Larson, Keith
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Klamath Bird Observatory, 320 Beach Street, Ashland, Oregon, 97520, USA.
    Migratory Connectivity of North American Caspian Tern (Hydroprogne caspia) Populations2017In: Waterbirds (De Leon Springs, Fla.), ISSN 1524-4695, E-ISSN 1938-5390, Vol. 40, no 1, p. 58-62Article in journal (Refereed)
    Abstract [en]

    Migratory connectivity of Caspian Terns (Hydroprogne caspia) was investigated using individuals marked in North America between 1922 and 2015. The results support recent genetic work describing three breeding regions (Pacific, Great Lakes, and Central Canada). Further., our results show strong migratory connectivity of Pacific breeders to wintering regions in central and western Mexico, and connectivity of Great Lakes breeders to wintering regions in the Gulf of Mexico and Caribbean. This integrated picture of demographic connectivity throughout North America should help in planning more effective management of the species.

  • 228. Cromsigt, Joris PGM
    et al.
    te Beest, Mariska
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Restoration of a megaherbivore: landscape-level impacts of white rhinoceros in Kruger National Park, South Africa2014In: Journal of Ecology, ISSN 0022-0477, E-ISSN 1365-2745, Vol. 102, no 3, p. 566-575Article in journal (Refereed)
    Abstract [en]

    Megaherbivores have been lost from most ecosystems world-wide, and current increases in poaching of rhino and elephant spp. threaten their status in the systems where they still occur. Although megaherbivores are said to be key drivers of ecosystem structure and functioning, empirical evidence is strongly biased to studies on African elephant. We urgently need a better understanding of the impact of other megaherbivore species to predict the consequences of megaherbivore loss. We used a unique 'recolonization experiment' to test how a megagrazer, white rhinoceros, is affecting the structure of savanna grasslands in Kruger National Park (KNP). With a 30-year record of rhinoceros distribution, we quantified how they recolonized KNP following their re-introduction. This allowed us to identify landscapes with high rhino densities and long time since recolonization versus landscapes with low rhino densities that were recolonized more recently but were otherwise biophysically similar. We recorded grassland heterogeneity on 40transects covering a total of 30km distributed across both landscapes. We used two proxies of grassland heterogeneity: % short grass cover and number of grazing lawn patches. Grazing lawns are patches with specific communities of prostrate-growing stoloniferous short grass species. Short grass cover was clearly higher in the high rhino impact (17.5%) than low rhino impact landscape (10.7%). Moreover, we encountered ~20 times more grazing lawns in the high rhino impact landscape. The effect of rhino on number of lawns and on short grass cover was similar to the two dominant geologies in KNP, basalt-derived versus granite-derived soils. Synthesis. We provide empirical evidence that white rhinoceros may have started to change the structure and composition of KNP's savanna grasslands. It remains to be tested if these changes lead to other ecological cascading effects. However, our results highlight that the current rhino poaching crisis may not only affect the species, but also threaten the potential key role of this megaherbivore as a driver of savanna functioning.

  • 229.
    Crona, Johanna
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Use of measured respiration rate over time to estimate growth rate of planktonic animals2007Independent thesis Advanced level (degree of Master (One Year)), 20 credits / 30 HE creditsStudent thesis
  • 230.
    Cunningham, L.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Vogel, H.
    Wennrich, V.
    Juschus, O.
    Nowaczyk, N.
    Rosen, Peter
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Amplified bioproductivity during Transition IV (332 000-342 000 yr ago): evidence from the geochemical record of Lake El'gygytgyn2013In: Climate of the Past, ISSN 1814-9324, E-ISSN 1814-9332, Vol. 9, no 2, p. 679-686Article in journal (Refereed)
    Abstract [en]

    To date, terrestrial archives of long-term climatic change within the Arctic have widely been restricted to ice cores from Greenland and, more recently, sediments from Lake El'gygytgyn in northeast Arctic Russia. Sediments from this lake contain a paleoclimate record of glacial-interglacial cycles during the last three million years. Low-resolution studies at this lake have suggested that changes observed during Transition IV (the transition from marine isotope stage (MIS) 10 to MIS 9) are of greater amplitude than any observed since. In this study, geochemical parameters are used to infer past climatic conditions thus providing the first high-resolution analyses of Transition IV from a terrestrial Arctic setting. These results demonstrate that a significant shift in climate was subsequently followed by a rapid increase in biogenic silica (BSi) production. Following this sharp increase, bioproductivity remained high, but variable, for over a thousand years. This study reveals differences in the timing and magnitude of change within the ratio of silica to titanium (Si/Ti) and BSi records that would not be apparent in lower resolution studies. This has significant implications for the increasingly common use of Si/Ti data as an alternative to traditional BSi measurements.

  • 231.
    Dahlberg, Helena
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Faderskapsanalys av tallfrö från Västerhus fröplantage: Skillnad i pollenkontaminering mellan öppen pollinering och pollinering inom ett avgränsat system2014Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    In this study, pollen contamination (measured by the number of seeds pollinated by pollen not belonging to any of the clones on the seed orchard) is compared between open pollination and isolated pollination environments in a Scots pine (Pinus sylvestris) seed orchard called Västerhus, located outside Önsköldsvik. In this seed orchard a tent experiment is taking place. Skogforsk has built six large tents covering 12-14 trees with each tent. Fertilization patterns were compared between one tree in a tent with a supplementation of pollen from five clones not represented in the tent and another tree of the same clone subject to open pollination outside the tents. By using DNA markers the paternity was determined for 48 seeds from each tree. The results show a big difference in pollen contamination between the two trees. The tree inside the tent showed a contamination rate of 0% and the tree from the open pollination had a contamination rate of 20,5%. No difference was found in the numbers of different fathers although the selfing rate of 4,26% was higher in the tent than the selfing rate of 2,56% observed in the open pollination environment. These results match the results of other studies done on the same orchard pretty well and therefore tent isolation with a supplementary pollination can be a good way to reduce unwanted pollen contamination.

  • 232.
    Dahlberg, Helena
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Faderskapsanalys av tallfrö från Västerhus fröplantage: Skillnaden i pollenkontaminering mellan öppen pollinering och pollinering inom ett avgränsat system2014Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    In this study, pollen contamination (measured by the number of seeds pollinated by pollen not belonging to any of the clones on the seed orchard) is compared between open pollination and isolated pollination environments in a Scots pine (Pinus sylvestris) seed orchard called Västerhus, located outside Önsköldsvik. In this seed orchard a tent experiment is taking place. Skogforsk has built six large tents covering 12-14 trees with each tent. Fertilization patterns were compared between one tree in a tent with a supplementation of pollen from five clones not represented in the tent and another tree of the same clone subject to open pollination outside the tents. By using DNA markers the paternity was determined for 48 seeds from each tree. The results show a big difference in pollen contamination between the two trees. The tree inside the tent showed a contamination rate of 0% and the tree from the open pollination had a contamination rate of 20,5%. No difference was found in the numbers of different fathers although the selfing rate of 4,26% was higher in the tent than the selfing rate of 2,56% observed in the open pollination environment. These results match the results of other studies done on the same orchard pretty well and therefore tent isolation with a supplementary pollination can be a good way to reduce unwanted pollen contamination.

  • 233.
    Dahlberg, Lars
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Evaluation of methods for quantification of pendulous epiphytic lichens2008Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
  • 234.
    Dahlgren, Jonas
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Interactions between gray-sided voles (Clethrionomys rufocanus) and vegetation in the Fennoscandian tundra2006Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    I have, in this thesis, studied the interactions between gray-sided voles (Clethrionomys rufocanus) and tundra vegetation, on islands in, and mainland sites close to the lake Iešjávri, in northern Norway. As isolated islands are virtually free of predation, I have been able to compare plant-herbivore interactions in the presence and absence of predators. I transplanted vegetation from an island with predators and voles, to predator-free islands with and with out voles. The results reveal the existence of a terrestrial trophic cascade as voles had a severe impact on the transplanted vegetation on the predator-free islands, but only minor effects on the mainland where predators are present. Moreover, this study shows that plant defence was only a successful strategy when predators were present. Voles reduced the abundance of all available plants during winter on the predator-free islands. The results imply that cascading effects of predation are most important for well-defended plants with grazing-sensitive morphology as these plants escape herbivore impacts in the presence of predators but are vulnerable in their absence

    I studied the recovery of intensively grazed vegetation by building exclosures on islands that have been heavily grazed by voles for almost a decade.This study shows that the collective biomass of vascular plants recovered completely on three years, when voles were excluded. Although most species that are dominating the ungrazed vegetation recovered rapidly in the exclosures, the vegetation did not simply return to its ungrazed state. Herbaceous plants increased and there were pronounced differences in response among evergreen dwarf-shrub species. The semi-prostrate and tannin rich crowberry (Empetrum nigrum), showed the strongest recovery of all species, while the erect lingonberry (Vaccinium vitis-idaea) only showed weak signs of recovery. Thus, growth form determined the potential of plants to recover, whereas the trade-off between defensive investments and capacity to recover was weak or absent.

    I studied the interaction between gray-sided voles and their main winter food plant, bilberry (Vaccinium myrtillus) on islands in and mainland sites close to the lake Iešjávri. I compared the abundance, population structure and palatability of bilberry ramets between vole-free islands, islands with voles but no predators and mainland sites with both voles and predators. Voles decreased the abundance of bilberry on the mainland, but the effect was much stronger on predator-free islands. Bilberry was fairly tolerant to grazing as it partially compensated for the lost tissue by producing more new ramets. Moreover, a cafeteria experiment showed that voles preferred the ramets from predator-free islands, which is inconsistent with conjectures emphasizing inducible plant defenses. The vole-bilberry interaction lacks features of delayed density dependence that could explain the vole cycles. I conducted a clipping and fertilization experiment to further investigate the effects of herbivory on palatability of bilberry shoots. Fertilization decreased the concentration of condensed tannins in shoots of bilberry and voles preferred fertilized and clipped shoots. I found no indication of induced defense that could reduce the palatability of bilberry twigs in response to herbivory.

    The relationships between gray-sided vole densities, levels of invertebrate herbivory and chemical quality of leaves of Northern willow (Salix glauca) were studied on islands and mainland sites with contrasting vole densities. I found a positive correlation between level of invertebrate herbivory and vole density. The number of leaves per shoot, leaf size and leaf nitrogen content were also positively correlated with vole densities, while leaf C/N ratios were negatively correlated with vole densities. The positive correlation between vole densities and level of invertebrate herbivory is probably due to a facilitative effect of voles on invertebrate herbivores, mediated through changes in plant chemistry.

  • 235.
    Dahlgren, Jonas
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Oksanen, Lauri
    Oksanen, Tarja
    Olofsson, Johan
    Trophic cascades and direct herbivore impacts in a low arctic scrublandIn: American Naturalist, ISSN 0003-0147, E-ISSN 1537-5323Article in journal (Other academic)
  • 236.
    Dahlgren, Jonas
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Oksanen, Lauri
    Department of Biology, Section of Ecology, University of Turku, Turku, Finland.
    Oksanen, Tarja
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Olofsson, Johan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Hambäck, Peter A
    Department of Botany, Stockholm University, Stockholm, Sweden.
    Lindgren, Åsa
    Department of Botany, Stockholm University, Stockholm, Sweden.
    Plant defences to no avail?: Responses of plants of varying edibility to food web manipulations in a low arctic scrubland2009In: Evolutionary Ecology Research, ISSN 1522-0613, E-ISSN 1937-3791, Vol. 11, p. 1189-1203Article in journal (Refereed)
    Abstract [en]

    Background: According to the Green World Hypothesis of Hairston, Smith, and Slobodkin,all plants are edible for some herbivores. Hence, the copious abundance of plant biomass,typical for terrestrial ecosystems, depends on the collective regulatory action of predators on the herbivore guild. According to the counterarguments of Polis and Strong, the defensive traits of terrestrial plants attenuate terrestrial trophic cascades to species-specific trickles,so elimination of predators might lead to increased abundance of inedible plants but will not influence community-level plant biomass.

    Question: Does the elimination of predators from a low arctic scrubland, with high-quality forage plants and poorly edible evergreen ericoids, lead to a reduction of community-level plant biomass or to an increased abundance of well-defended evergreen ericoids?

    Methods: In 1991, we introduced grey-sided voles (Myodes rufocanus) to islands, initially harbouring dense scrubland vegetation, and established permanent plots there. In 2000, we transplanted vegetation blocks from a large three-trophic-level island with voles and predators,to two-trophic-level islands with introduced voles but without resident predators, and also to vole-free one-trophic-level islands, and back to the three-trophic-level island. Vole densities were monitored by semi-annual live trapping. Vegetation was monitored by the point-frequency method.

    Results: In the absence of predators, vole densities increased 3.7-fold and the communitylevel plant biomass was decimated. The least palatable plant group, evergreen ericoids,suffered especially heavily, whereas palatable herbaceous plants increased in abundance. However, all three functional plant groups responded positively to the elimination of grey-sided voles.

    Conclusions: Our results corroborate the Green World Hypothesis, indicating that in the absence of predators, plant defences do not prevent runaway consumption of the vegetation.

  • 237.
    Dahlgren, Kristin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Food web structures and carbon transfer efficiencies in a brackish water ecosystem2010Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Two differently structured food webs can be distinguished in the pelagic habitat of aquatic systems; the classical one (autotrophic) with phytoplankton as a base and the microbial food web (heterotrophic) with bacteria as a base. Energy (produced at the basal trophic level) reaches higher trophic levels, i.e. zooplankton, directly in the classical food web in contrast to the microbial food web where it passes through additional trophic levels before reaching zooplankton. Energy is lost between each trophic level and therefore less energy should reach higher trophic levels in the microbial food web than in the classical food web. However, factors such as edibility of prey, temperature and properties of the predator, might also influence the food web structures and functions.

    In this thesis I studied which factors are important for an efficient carbon transfer and how a potential climate change might alter the food web efficiency in pelagic and pelagic-benthic food webs in the Baltic Sea. Furthermore, one of the most dominant zooplankton in the northern Baltic Sea, Limnocalanus macrurus, was studied in order to establish the seasonal pattern of lipid reserves in relation to food consumption.

    My studies showed that the carbon transfer efficiency during summer was not directly connected to the basal production, but factors such as the ratio between heterotrophs and autotrophs, the relationship between cladocerans and calanoid copepods and the size and community structure of both phytoplankton and zooplankton were important for the carbon transfer efficiency. In a climate change perspective, the temperature as well as the relative importance of the microbial food web is likely to increase. A temperature increase may have a positive effect on the pelagic food web efficiency, whereas increasing heterotrophy will have a negative effect on the pelagic and pelagic-benthic food web efficiency, reduce the fatty acid content of zooplankton and reduce the individual weight of both zooplankton and the benthic amphipod Monoporeia affinis. During the seasonal study on the calanoid copepod L. macrurus, I found that this species is mainly a carnivore, feeding on mesozooplankton during most of the year but switches to feeding on phytoplankton when these are abundant. Furthermore, when food is scarce, it utilizes lipids that are built up during the course of the year.

    From these studies I can draw some major conclusions; there are many factors that influence how efficient carbon is transferred in the food web and different factors are probably of various importance in different areas. In order to determine the carbon transfer efficiency, the various strategies exerted by different organism groups have to be considered, as for example that some zooplankton utilize lipid reserves instead of feeding all year around. Also, in a climate change perspective, the pelagic-benthic food web efficiency will decrease, as will the quality of zooplankton and M. affinis, possibly having implications for higher trophic levels such as fish.

  • 238.
    Dahlgren, Kristin
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Umeå University, Faculty of Science and Technology, Umeå Marine Sciences Centre (UMF).
    Andersson, Agneta
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Umeå University, Faculty of Science and Technology, Umeå Marine Sciences Centre (UMF).
    Larsson, Ulf
    Department of Systems Ecology, Stockholm University, 10691 Stockholm, Sweden.
    Hajdu, Susanna
    Department of Systems Ecology, Stockholm University, 10691 Stockholm, Sweden.
    Båmstedt, Ulf
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Umeå University, Faculty of Science and Technology, Umeå Marine Sciences Centre (UMF).
    Planktonic production and carbon transfer efficiency along a north-south gradient in the Baltic sea2010In: Marine Ecology Progress Series, ISSN 0171-8630, E-ISSN 1616-1599, Vol. 409, p. 77-94Article in journal (Refereed)
    Abstract [en]

    A 1 yr study was conducted along a brackish-water production gradient to enhance the understanding of factors governing pelagic food web function. This was achieved by measuring carbon transfer efficiency (TE) from the basal resource to an intermediate trophic level. TE was defined as mesozooplankton carbon consumption rate divided by production at the basal trophic level, which is composed of phytoplankton and bacteria. A north–south transect in the Baltic Sea was used as a model system, with 2 stations each in the Bothnian Bay, Bothnian Sea and Baltic Proper being sampled 5 to 8× during 2006. In addition, data from monitoring programmes were used, which comprised 10 to 22 samplings stn–1. TE was expected to be governed by the size distribution of phytoplankton and due to the nutrient gradient, we expected to find an optimal cell size, and thus also a high TE, in the intermediate-productive Bothnian Sea. The basal production during summer/autumn increased 5-fold from north to south, while the mesozooplankton carbon consumption rate exhibited a peak inthe Bothnian Sea, being ~3× higher than in both Bothnian Bay and Baltic Proper. TE was found to be intermediate in the Bothnian Bay (average: 0.8), highest in the Bothnian Sea (1.6), and lowest in the Baltic Proper (0.2). We suggest that the variation in carbon transfer efficiency can be explained by the composition of the phytoplankton community, the abundance balance between copepods and cladocerans, as well as the species composition of mesozooplankton in relation to the size structure of phytoplankton.

  • 239.
    Dahlgren, Kristin
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Eriksson Wiklund, Ann-Kristin
    Department of Applied Environmental Science, ITM, Stockholm University, 106 91 Stockholm, Sweden.
    Andersson, Agneta
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Umeå University, Faculty of Science and Technology, Umeå Marine Sciences Centre (UMF).
    Influence of plankton structure and temperature on pelagic food web efficiency in a brackish water system2011In: Aquatic Ecology, ISSN 1386-2588, E-ISSN 1573-5125, Vol. 45, p. 307-323Article in journal (Refereed)
    Abstract [en]

    As part of one climate change scenario, water temperature as well as the ratio between heterotrophic and autotrophic production is expected to increase; the latter at least in higher latitudes. In order to test how this scenario would affect organisms, such as metazooplankton, at higher trophic levels and carbon transfer up the food chain, a mesocosm experiment was performed at two different temperatures; 5 and 10°C, with two food webs; one phytoplankton-based (NP; autotrophic) and one bacteria-based (CNP; heterotrophic).  The groups of pelagic organisms included in the mesocosms were bacteria, flagellates, ciliates, phytoplankton and metazooplankton. Metazooplankton production was observed to increase with temperature, but was not significantly affected by food web structure. A change in food web structure, i.e. increased heterotrophy, did however lead to decreased fatty acid content and lower individual weight of the metazooplankton. Food web efficiency (FWE), defined as metazooplankton production divided by basal production, increased with autotrophy and temperature: 5CNP (0.2%) < 10CNP (0.4%) < 5NP (1.2%) < 10NP (7.3%). Our results indicate that in the climate change scenario under consideration, the temperature will have a positive effect on FWE whereas the increase in heterotrophy will have a negative effect on FWE. Furthermore, the quality, in terms of fatty acid content and individual weight of the metazooplankton, will be reduced with possible negative effects on higher trophic levels.

  • 240.
    Dahlman, Lena
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Resource aquisition and allocation in lichens2003Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Lichens are fascinating symbiotic systems, where a fungus and a unicellular alga, most often green (bipartite green algal lichens; 90% of all lichens), or a fi lamentous cyanobacterium (bipartite cyanobacterial lichens; 10% of all lichens) form a new entity (a thallus) appearing as a new and integrated organism: in about 500 lichens the fungus is associated with both a cyanobacterium and an alga (tripartite lichens). In the thallus, the lichen bionts function both as individual organisms, and as a symbiont partner. Hence, in lichens, the participating partners must both be able to receive and acquire resources from the other partner(s) in a controlled way.

    Lichens are particularly successful in harsh terrestrial environments. In part this is related to their poikilohydric nature and subsequent ability to repeatedly become desiccated and hydrated. Metabolic activity, i.e. photosynthesis, respiration, and for cyanobacterial lichens N2-fixation, is limited to periods when the thallus is suffi ciently hydrated. Mineral nutrients are mainly acquired from dry or wet deposition directly on the thallus. Taken together it then appears that lichens are to a large extent passively controlled by their environment, making their control over resource allocation and acquisition particularly challenging.

    The aim of this thesis was to investigate resource acquisition and allocation processes in different lichens, and to see how these respond to changes in resource availability. This was done by following lichen growth in the fi eld during manipulation of water, light, and nutrient supply, and by assessing the responses of both the integrated thallus as well as the individual bionts. As a fi rst step, resource allocation and acquisition was investigated for a broad range of lichens aiming to determine the magnitude of metabolic variation across lichens. Seventy-fi ve lichen species were selected to cover as broad a spectrum as possible regarding taxonomy, morphology, habitat, and nitrogen requirements. The lichens had invested their nitrogen resources so that photosynthetic capacity matched respiratory carbon demand around a similar equilibrium across the contrasting species. Regulation of lichen growth was investigated in another study, using the two tripartite species Nephroma arcticum and Peltigera aphthosa, emphasizing the contribution of both internal and external factors. The empirical growth models for the two lichens were similar, showing that weight gain is to a higher extent dependent on those external factors that regulate their photosynthesis, whilst area gain is more controlled by internal factors, such as their nitrogen metabolism. This might be inferred from another study of the same species, where nitrogen manipulations resulted in an undisturbed weight gain, a similar resource allocation pattern between the bionts, but a distorted area gain.

    Aiming to investigate lichen nitrogen relations even further, lichens’ capacities to assimilate combined nitrogen in the form of ammonium, nitrate and amino acids were assessed using 14 contrasting boreal species. All these had the capacity to assimilate all the three nitrogen forms, with ammonium absorption being more passive, and nitrate uptake being low in bipartite cyanobacterial lichens. Differences in uptake capacities between species were more correlated to photobiont than to morphology or substrate preferences. Finally, to investigate intra-specifi c plasticity in relation to altered nutrient supply, resource investments between photo- and mycobiont were investigated in the two bipartite green algal lichens Hypogymnia physodes and and Platismatia glauca in a low and a high nutrient environ- in a low and a high nutrient environ- ment. In both species, more of the resources had been directed to the photobiont in the high nutrient environment also increasing their overall carbon status. Taken together, my studies indicate that in spite of the apparent passive environmental control on lichen metabolism, these symbiotic organisms are able to both optimize and control their resource acquisition and allocation processes.

  • 241.
    Dahlman, Lena
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Palmqvist, Kristin
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Growth in two foliose tripartite lichens Nephroma arcticum and Peltigera aphthosa: empirical modelling of external versus internal factors2003In: Functional Ecology, ISSN 0269-8463, E-ISSN 1365-2435, Vol. 17, no 6, p. 821-831Article in journal (Refereed)
    Abstract [en]

    1 To assess how internal and external factors contribute to lichen growth, light, water and nutrient supplies were manipulated during 3 months in the field for the lichens Nephroma arcticum (L.) Torss. and Peltigera aphthosa (L.) Willd. Concomitant measures of weight and area gain, microclimatic conditions and investments in photobiont vs mycobiont tissue were also conducted.

    2 In both lichens ≈80% of the variation in weight gain was explained by a linear regression model including light received during wet active periods, chlorophyll a concentration and area gain. All three parameters had a positive effect on weight gain.

    3 About 80% of the variation in area gain was explained by a model including variation in weight gain, initial thallus specific weight, ergosterol and chitin concentration. The model was identical for the two lichens, with a positive effect of weight gain and thallus specific weight and a negative effect of ergosterol and chitin.

    4 Peltigera aphthosa grew faster than N. arcticum when exposed to the same environmental conditions. This could be explained by its higher chlorophyll a to ergosterol ratio, and a greater water-holding capacity prolonging the active time in light.

  • 242.
    Dahlström, Niklas
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Function and dynamics of woody debris in boreal forest streams2005Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The work in this thesis deals with (1) the effects of woody debris on stream channel morphology and retention of organic material, and (2) the dynamics of woody debris and its relation to riparian forest history and composition. The studied stream reaches are situated in mature, productive forests in the boreal zone of Sweden.

    Wood variables were important predictors of the frequency of debris dams, pool area, the proportion of pools formed by wood, and variation in the bankfull channel width. Pools formed by woody debris were mainly created by damming and had larger surface areas and residual depths than pools formed by other agents. Stream reaches intersecting old-growth forest (with minor influence of forest management) had coarser and longer woody debris pieces, greater amounts of wood, more debris dams, and wood-formed pools compared to streams surrounded by forests influenced by selective logging.

    The influence of past forest management on the quality and quantity of woody debris in streams were analyzed by using dendrochrnological methods. Selective loggings and absence of forest fires after 1831 resulted in lower input rates and a gradual replacement of pine by sruce over time. Residence times in stream channels of woody debris (>10 cm in basal diameter) were long and the oldest dated pieces of pine and spruce were over 300 and 100 years, respectively.

    Dynamics of woody debris were explored by comparing wood volumes and characteristics between stream channels and their riparianforests and between old growth and managed sites. Wood volumes recorded in the stream channels exceeded, but were related to, the volumes found in the riparian forests. Limited input of woody debris by bank cutting and absence of slope processes suggest that recruitment processes of woody debri to stream channels are similar as in riparian forests and slow decay in channels results in greater volumes.

    The retentiveness of organic material in stream channels was examined by using release and capture experiments in multiple reaces during varying discharges using different sizes of leaf mimics. Sixty eight percent of the variation in retention was explained by a multiple regression model including discharge and leaf mimic siz. Between 44 and 80% of the variation in retention among reaches was explained by channel constraint, gravel coverage, and woody debris variables as the most important. Estimates from a partial least squares (PLS) model suggest an increase in mean transport distances by 22 to 53% in managed forest streams compared to old growth conditions and in a low wood scenario, mean transport distances increased by 38 to 99% with larger increases for higher discharges and larger particle sizes.

    To regain more pristine conditions of stream channels, management and restoration are needed to increase the amount of woody debris that recreates lost channel structures and increaes the retention of organic material.

  • 243. Dawson, Michael N.
    et al.
    Algar, Adam C.
    Antonelli, Alexandre
    Dávalos, Liliana M.
    Davis, Edward
    Early, Regan
    Guisan, Antoine
    Jansson, Roland
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Lessard, Jean-Philippe
    Marske, Katharine A.
    McGuire, Jenny L.
    Stigall, Alycia L.
    Swenson, Nathan G.
    Zimmermann, Niklaus E.
    Gavin, Daniel G.
    An horizon scan of biogeography2013In: Frontiers of Biogeography, ISSN 1948-6596, Vol. 5, no 2, p. 130-157Article in journal (Refereed)
    Abstract [en]

    The opportunity to reflect broadly on the accomplishments, prospects, and reach of a field may present itself relatively infrequently.  Each biennial meeting of the International Biogeography Society showcases ideas solicited and developed largely during the preceding year, by individuals or teams from across the breadth of the discipline.  Here, we highlight challenges, developments, and opportunities in biogeography that were summarized at or emerge from that biennial synthesis. We note the realized and potential impact of rapid data accumulation in several fields, a Renaissance for inter-disciplinary research, the importance of recognizing the evolution-ecology continuum across spatial and temporal scales and at different taxonomic, phylogenetic and functional levels, and re-exploration of classical assumptions and hypotheses using new tools. However, advances are taxonomically and geographically biased, key theoretical frameworks await development of tools for handling, or strategies for simplifying, the biological complexity seen in empirical systems. Current threats to biodiversity require unprecedented integration of knowledge and development of predictive capacity that may enable biogeography to unite its descriptive and hypothetico-deductive arms and establish a greater role within and outside academia.

  • 244. De Frenne, P
    et al.
    Kolb, A
    Verheyen, K
    Brunet, J
    Chabrerie, O
    Decocq, G
    Diekmann, M
    Eriksson, O
    Heinken, T
    Hermy, M
    Jõgar, Ü
    Stanton, S
    Zindel, Renate
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Zobel, M
    Graae, BJ
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Unraveling the effects of temperature, latitude and local environment on the reproduction of six forest herbs.2009In: Global Ecology and Biogeography, ISSN 1466-822X, E-ISSN 1466-8238, Vol. 18, no 6, p. 641-651Article in journal (Refereed)
    Abstract [en]

    Aim To investigate the effect of temperature, latitude and local environment on the reproductive traits of widespread perennial forest herbs to better understand the potential impacts of rising temperatures on their population dynamics and colonization capacities.

    Location Six regions along a latitudinal gradient from France to Sweden.

    Methods Within each region, we collected data from three to five populations of up to six species. For each species, several variables were recorded in each region (temperature, latitude) and population (local abiotic and biotic environmental variables), and seed production and germination were estimated. Resource investment in reproduction (RIR) was quantified as seed number × seed mass, while germinable seed output (GSO) was expressed as seed number × germination percentage. We performed linear regression and mixed effect models to investigate the effects of temperature (growing degree hours), latitude and local abiotic and biotic environment on RIR and GSO.

    Results Temperature and latitude explained most of the variation in RIR and GSO for early flowering species with a northerly distribution range edge (Anemone nemorosa, Paris quadrifolia and Oxalis acetosella). Reproduction of the more southerly distributed species (Brachypodium sylvaticum, Circaea lutetiana and Primula elatior), in contrast, was independent of temperature/latitude. In the late summer species, B. sylvaticum and C. lutetiana, variation in RIR and GSO was best explained by local environmental variables, while none of the investigated variables appeared to be related to reproduction in P. elatior.

    Main conclusions We showed that reproduction of only two early flowering, northerly distributed species was related to temperature. This suggests that the potential reproductive response of forest herbs to climate warming partly depends on their phenology and distribution, but also that the response is to some extent species dependent. These findings should be taken into account when predictions about future shifts in distribution range are made.

  • 245. De Frenne, Pieter
    et al.
    Brunet, Jörg
    Shevtsova, Anna
    Umeå University, Faculty of Medicine, Department of Medical Biochemistry and Biophysics.
    Kolb, Annette
    Graae, Bente J
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Chabrerie, Olivier
    Cousins, Sara AO
    Decocq, Guillaume
    De Schrijver, An
    Diekmann, Martin
    Gruwez, Robert
    Heinken, Thilo
    Hermy, Martin
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Stanton, Sharon
    Tack, Wesley
    Willaert, Justin
    Verheyen, Kris
    Temperature effects on forest herbs assessed by warmingand transplant experiments along a latitudinal gradient2011In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 17, no 10, p. 3240-3253Article in journal (Refereed)
    Abstract [en]

    Slow-colonizing forest understorey plants are probably not able to rapidly adjust their distribution range following large-scale climate change. Therefore, the acclimation potential to climate change within their actual occupied habitats will likely be key for their short- and long-term persistence. We combined transplant experiments along a latitudinal gradient with open-top chambers to assess the effects of temperature on phenology, growth and reproductive performance of multiple populations of slow-colonizing understorey plants, using the spring flowering geophytic forb Anemone nemorosa and the early summer flowering grass Milium effusum as study species. In both species, emergence time and start of flowering clearly advanced with increasing temperatures. Vegetative growth (plant height, aboveground biomass) and reproductive success (seed mass, seed germination and germinable seed output) of A. nemorosa benefited from higher temperatures. Climate warming may thus increase future competitive ability and colonization rates of this species. Apart from the effects on phenology, growth and reproductive performance of M. effusum generally decreased when transplanted southwards (e.g., plant size and number of individuals decreased towards the south) and was probably more limited by light availability in the south. Specific leaf area of both species increased when transplanted southwards, but decreased with open-top chamber installation in A. nemorosa. In general, individuals of both species transplanted at the home site performed best, suggesting local adaptation. We conclude that contrasting understorey plants may display divergent plasticity in response to changing temperatures which may alter future understorey community dynamics.

  • 246. De Frenne, Pieter
    et al.
    Graae, Bente J
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Kolb, Annette
    Shevtsova, Anna
    Baeten, Lander
    Brunet, Jörg
    Chabrerie, Olivier
    Cousins, Sara A O
    Decocq, Guillaume
    Dhondt, Rob
    Diekmann, Martin
    Gruwez, Robert
    Heinken, Thilo
    Hermy, Martin
    Öster, Mathias
    Saguez, Robert
    Stanton, Sharon
    Tack, Wesley
    Vanhellemont, Margot
    Verheyen, Kris
    An intraspecific application of the leaf-height-seed ecology strategy scheme to forest herbs along a latitudinal gradient2011In: Ecography, ISSN 0906-7590, E-ISSN 1600-0587, Vol. 34, no 1, p. 132-140Article in journal (Refereed)
    Abstract [en]

    We measured LHS traits in 41 Anemone nemorosa and 44 Milium effusum populations along a 1900-2300 km latitudinal gradient from N France to N Sweden. We then applied multilevel models to identify the effects of regional (temperature, latitude) and local (soil fertility and acidity, overstorey canopy cover) environmental factors on LHS traits. Both species displayed a significant 4% increase in plant height with every degree northward shift (almost a two-fold plant height difference between the southernmost and northernmost populations). Neither seed mass nor SLA showed a significant latitudinal cline. Temperature had a large effect on the three LHS traits of Anemone. Latitude, canopy cover and soil nutrients were related to the SLA and plant height of Milium. None of the investigated variables appeared to be related to the seed mass of Milium. The variation in LHS traits indicates that the ecological strategy determined by the position of each population in this three-factor triangle is not constant along the latitudinal gradient. The significant increase in plant height suggests greater competitive abilities for both species in the northernmost populations. We also found that the studied environmental factors affected the LHS traits of the two species on various scales: spring-flowering Anemone was affected more by temperature, whereas early-summer flowering Milium was affected more by local and other latitude-related factors. Finally, previously reported cross-species correlations between LHS traits and latitude were generally unsupported by our within-species approach.

  • 247.
    De La Torre, Amanda
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Vancouver, BC, Canada.
    Ingvarsson, Pär
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Aitken, S. N.
    Vancouver, BC, Canada.
    Genetic architecture and genomic patterns of gene flow between hybridizing species of Picea2015In: Heredity, ISSN 0018-067X, E-ISSN 1365-2540, Vol. 115, no 2, p. 153-164Article in journal (Refereed)
    Abstract [en]

    Hybrid zones provide an opportunity to study the effects of selection and gene flow in natural settings. We employed nuclear microsatellites (single sequence repeat (SSR)) and candidate gene single-nucleotide polymorphism markers (SNPs) to characterize the genetic architecture and patterns of interspecific gene flow in the Picea glauca x P. engelmannii hybrid zone across a broad latitudinal (40-60 degrees) and elevational (350-3500 m) range in western North America. Our results revealed a wide and complex hybrid zone with broad ancestry levels and low interspecific heterozygosity, shaped by asymmetric advanced-generation introgression, and low reproductive barriers between parental species. The clinal variation based on geographic variables, lack of concordance in clines among loci and the width of the hybrid zone points towards the maintenance of species integrity through environmental selection. Congruency between geographic and genomic clines suggests that loci with narrow clines are under strong selection, favoring either one parental species (directional selection) or their hybrids (overdominance) as a result of strong associations with climatic variables such as precipitation as snow and mean annual temperature. Cline movement due to past demographic events (evidenced by allelic richness and heterozygosity shifts from the average cline center) may explain the asymmetry in introgression and predominance of P. engelmannii found in this study. These results provide insights into the genetic architecture and fine-scale patterns of admixture, and identify loci that may be involved in reproductive barriers between the species.

  • 248. De Laender, Frederik
    et al.
    Melian, Carlos J.
    Bindler, Richard
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Van den Brink, Paul J.
    Daam, Michiel
    Roussel, Helene
    Juselius, Jonas
    Verschuren, Dirk
    Janssen, Colin R.
    The contribution of intra- and interspecific tolerance variability to biodiversity changes along toxicity gradients2014In: Ecology Letters, ISSN 1461-023X, E-ISSN 1461-0248, Vol. 17, no 1, p. 72-81Article in journal (Refereed)
    Abstract [en]

    The worldwide distribution of toxicants is an important yet understudied driver of biodiversity, and the mechanisms relating toxicity to diversity have not been adequately explored. Here, we present a community model integrating demography, dispersal and toxicant-induced effects on reproduction driven by intraspecific and interspecific variability in toxicity tolerance. We compare model predictions to 458 species abundance distributions (SADs) observed along concentration gradients of toxicants to show that the best predictions occur when intraspecific variability is five and ten times higher than interspecific variability. At high concentrations, lower settings of intraspecific variability resulted in predictions of community extinction that were not supported by the observed SADs. Subtle but significant species losses at low concentrations were predicted only when intraspecific variability dominated over interspecific variability. Our results propose intraspecific variability as a key driver for biodiversity sustenance in ecosystems challenged by environmental change.

  • 249. De Long, Jonathan R.
    et al.
    Dorrepaal, Ellen
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Kardol, Paul
    Nilsson, Marie-Charlotte
    Teuber, Laurenz M.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Wardle, David A.
    Contrasting Responses of Soil Microbial and Nematode Communities to Warming and Plant Functional Group Removal Across a Post-fire Boreal Forest Successional Gradient2016In: Ecosystems (New York. Print), ISSN 1432-9840, E-ISSN 1435-0629, Vol. 19, no 2, p. 339-355Article in journal (Refereed)
    Abstract [en]

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

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

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

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  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf