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  • 1. Delling, B.
    et al.
    Palm, S.
    Palkopoulou, E.
    Prestegaard, T.
    Genetic signs of multiple colonization events in Baltic ciscoes with radiation into sympatric spring- and autumn-spawners confined to early postglacial arrival2014In: Ecology and Evolution, E-ISSN 2045-7758, Vol. 4Article in journal (Refereed)
    Abstract [en]

    Presence of sympatric populations may reflect local diversification or secondary contact of already distinct forms. The Baltic cisco (Coregonus albula) normally spawns in late autumn, but in a few lakes in Northern Europe sympatric autumn and spring- or winter-spawners have been described. So far, the evolutionary relationships and taxonomic status of these main life history forms have remained largely unclear. With microsatellites and mtDNA sequences, we analyzed extant and extinct spring- and autumn-spawners from a total of 23 Swedish localities, including sympatric populations. Published sequences from Baltic ciscoes in Germany and Finland, and Coregonus sardinella from North America were also included together with novel mtDNA sequences from Siberian C.sardinella. A clear genetic structure within Sweden was found that included two population assemblages markedly differentiated at microsatellites and apparently fixed for mtDNA haplotypes from two distinct clades. All sympatric Swedish populations belonged to the same assemblage, suggesting parallel evolution of spring-spawning rather than secondary contact. The pattern observed further suggests that postglacial immigration to Northern Europe occurred from at least two different refugia. Previous results showing that mtDNA in Baltic cisco is paraphyletic with respect to North American C.sardinella were confirmed. However, the inclusion of Siberian C.sardinella revealed a more complicated pattern, as these novel haplotypes were found within one of the two main C.albula clades and were clearly distinct from those in North American C.sardinella. The evolutionary history of Northern Hemisphere ciscoes thus seems to be more complex than previously recognized.

  • 2. Kristensen, Jeppe A.
    et al.
    Michelsen, Anders
    Metcalfe, Daniel B.
    Background insect herbivory increases with local elevation but makes minor contribution to element cycling along natural gradients in the Subarctic2020In: Ecology and Evolution, E-ISSN 2045-7758, Vol. 10, no 20, p. 11684-11698Article in journal (Refereed)
    Abstract [en]

    Herbivores can exert major controls over biogeochemical cycling. As invertebrates are highly sensitive to temperature shifts (ectothermal), the abundances of insects in high-latitude systems, where climate warming is rapid, is expected to increase. In subarctic mountain birch forests, research has focussed on geometrid moth outbreaks, while the contribution of background insect herbivory (BIH) to elemental cycling is poorly constrained. In northern Sweden, we estimated BIH along 9 elevational gradients distributed across a gradient in regional elevation, temperature, and precipitation to allow evaluation of consistency in local versus regional variation. We converted foliar loss via BIH to fluxes of C, nitrogen (N), and phosphorus (P) from the birch canopy to the soil to compare with other relevant soil inputs of the same elements and assessed different abiotic and biotic drivers of the observed variability. We found that leaf area loss due to BIH was ~1.6% on average. This is comparable to estimates from tundra, but considerably lower than ecosystems at lower latitudes. The C, N, and P fluxes from canopy to soil associated with BIH were 1?2 orders of magnitude lower than the soil input from senesced litter and external nutrient sources such as biological N fixation, atmospheric deposition of N, and P weathering estimated from the literature. Despite the minor contribution to overall elemental cycling in subarctic birch forests, the higher quality and earlier timing of the input of herbivore deposits to soils compared to senesced litter may make this contribution disproportionally important for various ecosystem functions. BIH increased significantly with leaf N content as well as local elevation along each transect, yet showed no significant relationship with temperature or humidity, nor the commonly used temperature proxy, absolute elevation. The lack of consistency between the local and regional elevational trends calls for caution when using elevation gradients as climate proxies.

  • 3. Lang, Simone I.
    et al.
    Aerts, Rien
    van Logtestijn, Richard S. P.
    Schweikert, Wenka
    Klahn, Thorsten
    Quested, Helen M.
    van Hal, Jurgen R.
    Cornelissen, Johannes H. C.
    Mapping nutrient resorption efficiencies of subarctic cryptogams and seed plants onto the Tree of Life2014In: Ecology and Evolution, E-ISSN 2045-7758, Vol. 4, no 11, p. 2217-2227Article in journal (Refereed)
    Abstract [en]

    Nutrient resorption from senescing photosynthetic organs is a powerful mechanism for conserving nitrogen (N) and phosphorus (P) in infertile environments. Evolution has resulted in enhanced differentiation of conducting tissues to facilitate transport of photosynthate to other plant parts, ultimately leading to phloem. Such tissues may also serve to translocate N and P to other plant parts upon their senescence. Therefore, we hypothesize that nutrient resorption efficiency (RE, % of nutrient pool exported) should correspond with the degree of specialization of these conducting tissues across the autotrophic branches of the Tree of Life. To test this hypothesis, we had to compare members of different plant clades and lichens within a climatic region, to minimize confounding effects of climatic drivers on nutrient resorption. Thus, we compared RE among wide-ranging basal clades from the principally N-limited subarctic region, employing a novel method to correct for mass loss during senescence. Even with the limited numbers of species available for certain clades in this region, we found some consistent patterns. Mosses, lichens, and lycophytes generally showed low REN (<20%), liverworts and conifers intermediate (40%) and monilophytes, eudicots, and monocots high (>70%). REP appeared higher in eudicots and liverworts than in mosses. Within mosses, taxa with more efficient conductance also showed higher REN. The differences in REN among clades broadly matched the degree of specialization of conducting tissues. This novel mapping of a physiological process onto the Tree of Life broadly supports the idea that the evolution of conducting tissues toward specialized phloem has aided land plants to optimize their internal nitrogen recycling. The generality of evolutionary lines in conducting tissues and nutrient resorption efficiency needs to be tested across different floras in different climatic regions with different levels of N versus P availability.

  • 4.
    Lindén, Elin
    et al.
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Gough, Laura
    Department of Biological Sciences, Towson University, MD, Towson, United States.
    Olofsson, Johan
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Large and small herbivores have strong effects on tundra vegetation in Scandinavia and Alaska2021In: Ecology and Evolution, E-ISSN 2045-7758, Vol. 11, no 17, p. 12141-12152Article in journal (Refereed)
    Abstract [en]

    Large and small mammalian herbivores are present in most vegetated areas in the Arctic and often have large impacts on plant community composition and ecosystem functioning. The relative importance of different herbivores and especially how their specific impact on the vegetation varies across the Arctic is however poorly understood. Here, we investigate how large and small herbivores influence vegetation density and plant community composition in four arctic vegetation types in Scandinavia and Alaska. We used a unique set of exclosures, excluding only large (reindeer and muskoxen) or all mammalian herbivores (also voles and lemmings) for at least 20 years. We found that mammalian herbivores in general decreased leaf area index, NDVI, and abundance of vascular plants in all four locations, even though the strength of the effect and which herbivore type caused these effects differed across locations. In three locations, herbivore presence caused contrasting plant communities, but not in the location with lowest productivity. Large herbivores had a negative effect on plant height, whereas small mammalian herbivores increased species diversity by decreasing dominance of the initially dominating plant species. Above- or belowground disturbances caused by herbivores were found to play an important role in shaping the vegetation in all locations. Synthesis: Based on these results, we conclude that both small and large mammalian herbivores influence vegetation in Scandinavia and Alaska in a similar way, some of which can mitigate effects of climate change. We also see important differences across locations, but these depend rather on local herbivore and plant community composition than large biogeographical differences among continents.

  • 5.
    Markl, Gregor
    et al.
    Department of Geosciences, University of Tübingen, Tübingen, Germany.
    Ottmann, Shannon
    Haasis, Tobias
    Budach, Daniela
    Krais, Stefanie
    Köhler, Heinz-R.
    Thermobiological effects of temperature-induced color variations in Aglais urticae (Lepidoptera, Nymphalidae)2022In: Ecology and Evolution, E-ISSN 2045-7758, Vol. 12, no 6Article in journal (Refereed)
    Abstract [en]

    Coloration of animals is important for camouflage, for social behavior, or for physiological fitness. This study investigates the color variation in adults of Aglais urticae obtained on subjecting some pre-imaginal stages to different temperature conditions and their thermobiological consequences. To investigate the evolutionary?ecological interactions of temperature and pigmentation in butterflies, caterpillars, and pupae of the small tortoiseshell, Aglais urticae (Lepidoptera, Nymphalidae), larvae from Central Europe and Scandinavia were reared at temperatures between 7 and 34°C in the laboratory or in the field. After emergence, the intensity of pigmentation of the imagines and their increase in body temperature under defined full-spectrum light irradiation were quantified by image analysis and thermal imaging. At constant conditions, ambient rearing temperature and pigmentation intensity of imagines were negatively and linearly correlated in Central European butterflies, regardless of whether the pupal stage alone or, additionally, the last period of the larval stage was exposed to these conditions: low temperatures induced darker coloration and high temperatures led to lighter individuals. A thermal pulse of a few days alone at the beginning of pupal dormancy led to a similar, albeit weakened, effect. Caterpillars of the Scandinavian subspecies A. urticae polaris, whose pupal dormancy took place under Central European field conditions, developed into strongly pigmented imagines. The thermobiological relevance of more intense pigmentation was shown by significantly higher absorption of light, and thus stronger increased body temperature after 5 min of defined illumination, but this difference ceased after 15 min. Our results show that phenotypic plasticity in wing coloration is adaptive since temperature-induced developmental changes provide thermobiological benefit in adult butterflies. We propose that, in subpolar latitudes, darker coloration likely has a selection advantage favoring individuals with reaction norms gradually shifted to stronger pigmented phenotypes, possibly leading to the establishment of a pigmentation cline.

  • 6. Naud, Lucy
    et al.
    Måsviken, Johannes
    Freire, Susana
    Angerbjörn, Anders
    Dalén, Love
    Dalerum, Fredrik
    Altitude effects on spatial components of vascular plant diversity in a subarctic mountain tundra2019In: Ecology and Evolution, E-ISSN 2045-7758, Vol. 9, no 8, p. 4783-4795Article in journal (Refereed)
    Abstract [en]

    Environmental gradients are caused by gradual changes in abiotic factors, which affect species abundances and distributions, and are important for the spatial distribution of biodiversity. One prominent environmental gradient is the altitude gradient. Understanding ecological processes associated with altitude gradients may help us to understand the possible effects climate change could have on species communities. We quantified vegetation cover, species richness, species evenness, beta diversity, and spatial patterns of community structure of vascular plants along altitude gradients in a subarctic mountain tundra in northern Sweden. Vascular plant cover and plant species richness showed unimodal relationships with altitude. However, species evenness did not change with altitude, suggesting that no individual species became dominant when species richness declined. Beta diversity also showed a unimodal relationship with altitude, but only for an intermediate spatial scale of 1 km. A lack of relationships with altitude for either patch or landscape scales suggests that any altitude effects on plant spatial heterogeneity occurred on scales larger than individual patches but were not effective across the whole landscape. We observed both nested and modular patterns of community structures, but only the modular patterns corresponded with altitude. Our observations point to biotic regulations of plant communities at high altitudes, but we found both scale dependencies and inconsistent magnitude of the effects of altitude on different diversity components. We urge for further studies evaluating how different factors influence plant communities in high altitude and high latitude environments, as well as studies identifying scale and context dependencies in any such influences.

  • 7.
    Prager, Case M.
    et al.
    Ecology and Evolutionary Biology Department, University of Michigan, MI, Ann Arbor, United States; The Rocky Mountain Biological Laboratory, CO, Crested Butte, United States.
    Classen, Aimee T.
    Ecology and Evolutionary Biology Department, University of Michigan, MI, Ann Arbor, United States; The Rocky Mountain Biological Laboratory, CO, Crested Butte, United States; Natural History Museum of Denmark, University of Copenhagen, Copenhagen, Denmark.
    Sundqvist, Maja K.
    Natural History Museum of Denmark, University of Copenhagen, Copenhagen, Denmark; Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Barrios-Garcia, Maria Noelia
    CONICET, CENAC-APN, Rio Negro, San Carlos de Bariloche, Argentina; Rubenstein School of Environment and Natural Resources, University of Vermont, VT, Burlington, United States.
    Cameron, Erin K.
    Department of Environmental Science, Saint Mary's University, NS, Halifax, Canada.
    Chen, Litong
    Qinghai Provincial Key Laboratory of Restoration Ecology of Cold Area and Key Laboratory of Adaptation and Evolution of Plant Biota, Northwest Institute of Plateau Biology, Chinese Academy of Sciences, Xining, China.
    Chisholm, Chelsea
    Department of Environment Systems Science, Institute of Integrative Biology, ETH Zürich, Zürich, Switzerland.
    Crowther, Thomas W.
    Department of Environment Systems Science, Institute of Integrative Biology, ETH Zürich, Zürich, Switzerland.
    Deslippe, Julie R.
    Centre for Biodiversity and Restoration Ecology, School of Biological Sciences, Victoria University of Wellington, Wellington, New Zealand.
    Grigulis, Karl
    Laboratoire d'Ecologie Alpine, Université Grenoble Alpes – CNRS – Université Savoie Mont-Blanc, Grenoble, France.
    He, Jin-Sheng
    Department of Ecology, College of Urban and Environmental Sciences, Peking University, Beijing, China.
    Henning, Jeremiah A.
    The Rocky Mountain Biological Laboratory, CO, Crested Butte, United States; Department of Biology, University of South Alabama, AL, Mobile, United States.
    Hovenden, Mark
    Biological Sciences, School of Natural Sciences, University of Tasmania, TAS, Hobart, Australia.
    Høye, Toke T. Thomas
    Department of Ecoscience and Arctic Research Centre, Aarhus University, Aarhus C, Denmark.
    Jing, Xin
    Natural History Museum of Denmark, University of Copenhagen, Copenhagen, Denmark; State Key Laboratory of Grassland Agro-Ecosystems, and College of Pastoral Agriculture Science and Technology, Lanzhou University, Gansu, Lanzhou, China.
    Lavorel, Sandra
    Laboratoire d'Ecologie Alpine, Université Grenoble Alpes – CNRS – Université Savoie Mont-Blanc, Grenoble, France.
    McLaren, Jennie R.
    Department of Biological Sciences, University of Texas at El Paso, TX, El Paso, United States.
    Metcalfe, Daniel B.
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Newman, Gregory S.
    Department of Biology, University of Oklahoma, OK, Norman, United States.
    Nielsen, Marie Louise
    Department of Ecoscience and Arctic Research Centre, Aarhus University, Aarhus C, Denmark.
    Rixen, Christian
    Mountain Ecosystems Group, WSL Institute for Snow and Avalanche Research SLF, Davos Dorf, Switzerland.
    Read, Quentin D.
    The Rocky Mountain Biological Laboratory, CO, Crested Butte, United States; National Socio-Environmental Synthesis Center, MD, Annapolis, United States.
    Rewcastle, Kenna E.
    Rubenstein School of Environment and Natural Resources, University of Vermont, VT, Burlington, United States.
    Rodriguez-Cabal, Mariano
    Rubenstein School of Environment and Natural Resources, University of Vermont, VT, Burlington, United States; Grupo de Ecología de Invasiones, INIBIOMA, CONICET, Universidad Nacional del Comahue, San Carlos de Bariloche, Argentina.
    Wardle, David A.
    Asian School of the Environment, Nanyang Technological University, Singapore, Singapore.
    Wipf, Sonja
    Department of Biology, University of Oklahoma, OK, Norman, United States; Department of Research and Monitoring, Chastè Planta-Wildenberg, Zernez, Switzerland.
    Sanders, Nathan J.
    Ecology and Evolutionary Biology Department, University of Michigan, MI, Ann Arbor, United States; The Rocky Mountain Biological Laboratory, CO, Crested Butte, United States; Natural History Museum of Denmark, University of Copenhagen, Copenhagen, Denmark.
    Integrating natural gradients, experiments, and statistical modeling in a distributed network experiment: An example from the WaRM Network2022In: Ecology and Evolution, E-ISSN 2045-7758, Vol. 12, no 10, article id e9396Article in journal (Refereed)
    Abstract [en]

    A growing body of work examines the direct and indirect effects of climate change on ecosystems, typically by using manipulative experiments at a single site or performing meta-analyses across many independent experiments. However, results from single-site studies tend to have limited generality. Although meta-analytic approaches can help overcome this by exploring trends across sites, the inherent limitations in combining disparate datasets from independent approaches remain a major challenge. In this paper, we present a globally distributed experimental network that can be used to disentangle the direct and indirect effects of climate change. We discuss how natural gradients, experimental approaches, and statistical techniques can be combined to best inform predictions about responses to climate change, and we present a globally distributed experiment that utilizes natural environmental gradients to better understand long-term community and ecosystem responses to environmental change. The warming and (species) removal in mountains (WaRM) network employs experimental warming and plant species removals at high- and low-elevation sites in a factorial design to examine the combined and relative effects of climatic warming and the loss of dominant species on community structure and ecosystem function, both above- and belowground. The experimental design of the network allows for increasingly common statistical approaches to further elucidate the direct and indirect effects of warming. We argue that combining ecological observations and experiments along gradients is a powerful approach to make stronger predictions of how ecosystems will function in a warming world as species are lost, or gained, in local communities.

  • 8. Scharn, Ruud
    et al.
    Negri, Isabel S.
    Sundqvist, Maja K.
    Løkken, Jørn O.
    Bacon, Christine D.
    Antonelli, Alexandre
    Hofgaard, Annika
    Nilsson, R. Henrik
    Björk, Robert G.
    Limited decadal growth of mountain birch saplings has minor impact on surrounding tundra vegetation2022In: Ecology and Evolution, E-ISSN 2045-7758, Vol. 12, no 6, article id e9028Article in journal (Refereed)
    Abstract [en]

    Temperatures over the Arctic region are increasing at three times the rate of the global average. Consequently, Arctic vegetation is changing and trees are encroaching into the tundra. In this study, we examine the establishment and growth of mountain birch (Betula pubescens ssp. tortuosa), which forms the treeline in subarctic Europe, and its impact on community composition across the treeline ecotone nearby Abisko, Sweden. Birch advancement along elevational gradients was studied by comparing data collected in 2016 with data collected 10 and 15 years previously. Species identity, cover, and phylogenetic relatedness were used to assess the impact of birch encroachment on community composition. Our results show that birch occurrence above the treeline did not affect plant community composition, probably owing to the observed lack of significant growth due to herbivore browsing, nitrogen limitation, or a reduction in snow cover. Independent of birch performance, the tundra community structure shifted toward a novel community dissimilar from the forest plant community found below the treeline. Taken together, our findings are explained by species-specific responses to climate change, rather than by a linear forest advance. Future treeline advancements are likely more restricted than previously expected.

  • 9. Träger, Sabrina
    et al.
    Milbau, Ann
    Wilson, Scott D.
    Potential contributions of root decomposition to the nitrogen cycle in arctic forest and tundra2017In: Ecology and Evolution, E-ISSN 2045-7758Article in journal (Refereed)
    Abstract [en]

    Plant contributions to the nitrogen (N) cycle from decomposition are likely to be altered by vegetation shifts associated with climate change. Roots account for the majority of soil organic matter input from vegetation, but little is known about differences between vegetation types in their root contributions to nutrient cycling. Here, we examine the potential contribution of fine roots to the N cycle in forest and tundra to gain insight into belowground consequences of the widely observed increase in woody vegetation that accompanies climate change in the Arctic. We combined measurements of root production from minirhizotron images with tissue analysis of roots from differing root diameter and color classes to obtain potential N input following decomposition. In addition, we tested for changes in N concentration of roots during early stages of decomposition, and investigated whether vegetation type (forest or tundra) affected changes in tissue N concentration during decomposition. For completeness, we also present respective measurements of leaves. The potential N input from roots was twofold greater in forest than in tundra, mainly due to greater root production in forest. Potential N input varied with root diameter and color, but this variation tended to be similar in forest and tundra. As for roots, the potential N input from leaves was significantly greater in forest than in tundra. Vegetation type had no effect on changes in root or leaf N concentration after 1 year of decomposition. Our results suggest that shifts in vegetation that accompany climate change in the Arctic will likely increase plant-associated potential N input both belowground and aboveground. In contrast, shifts in vegetation might not alter changes in tissue N concentration during early stages of decomposition. Overall, differences between forest and tundra in potential contribution of decomposing roots to the N cycle reinforce differences between habitats that occur for leaves.

  • 10. Virtanen, Risto
    et al.
    Oksanen, Lauri
    Oksanen, Tarja
    Cohen, Juval
    Forbes, Bruce C.
    Johansen, Bernt
    Käyhkö, Jukka
    Olofsson, Johan
    Pulliainen, Jouni
    Tømmervik, Hans
    Where do the treeless tundra areas of northern highlands fit in the global biome system: toward an ecologically natural subdivision of the tundra biome2016In: Ecology and Evolution, E-ISSN 2045-7758, Vol. 6, no 1, p. 143-158Article in journal (Refereed)
    Abstract [en]

    According to some treatises, arctic and alpine sub

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