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  • 1.
    Ask, Jenny
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Karlsson, Jan
    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.
    Ask, Per
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Byström, Pär
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jansson, Mats
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Whole-lake estimates of carbon flux through algae and bacteria in benthic and pelagic habitats of clear-water lakes2009In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 90, no 7, p. 1923-1932Article in journal (Refereed)
    Abstract [en]

    This study quantified new biomass production of algae and bacteria in both benthic and pelagic habitats of clear-water lakes to contrast how carbon from the atmosphere and terrestrial sources regulates whole-lake metabolism. We studied four small unproductive lakes in subarctic northern Sweden during one summer season. The production of new biomass in both benthic and pelagic habitats was calculated as the sum of autotrophic production by algae and heterotrophic production by bacteria using allochthonous organic carbon (OC). Whole-lake production of new biomass was dominated by the benthic habitat (86% +/- 4% [mean +/- SD]) and by primary production (77% +/- 9%). Still, heterotrophic bacteria fueled by allochthonous OC constituted a significant portion of the new biomass production in both benthic (19% +/- 11%) and pelagic habitats (51% +/- 24%). In addition, overall net production (primary production minus respiration) was close to zero in the benthic habitats but highly negative (-163 +/- 81 mg C.m(-2).d(-1)) in pelagic regions of all lakes. We conclude (1) that allochthonous OC supported a significant part of total production of new biomass in both pelagic and benthic habitats, (2) that benthic habitats dominated the whole-lake production of new biomass, and (3) that respiration and net CO2 production dominated the carbon flux of the pelagic habitats and biomass production dominated the benthic carbon flux. Taken together, these findings suggest that previous investigations have greatly underestimated the productivity of clear-water lakes when benthic autotrophic production and metabolism of allochthonous OC have not been measured.

  • 2.
    Bartels, Pia
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Cucherousset, Julien
    Steger, Kristin
    Eklöv, Peter
    Tranvik, Lars J
    Hillebrand, Helmut
    Reciprocal subsidies between freshwater and terrestrial ecosystems structure consumer resource dynamics2012In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 93, no 5, p. 1173-1182Article in journal (Refereed)
    Abstract [en]

    Cross-ecosystem movements of material and energy, particularly reciprocal resource fluxes across the freshwater-land interface, have received major attention. Freshwater ecosystems may receive higher amounts of subsidies (i.e., resources produced outside the focal ecosystem) than terrestrial ecosystems, potentially leading to increased secondary production in freshwaters. Here we used a meta-analytic approach to quantify the magnitude and direction of subsidy inputs across the freshwater-land interface and to determine subsequent responses in recipient animals. Terrestrial and freshwater ecosystems differed in the magnitude of subsidies they received, with aquatic ecosystems generally receiving higher subsidies than terrestrial ecosystems. Surprisingly, and despite the large discrepancy in magnitude, the contribution of these subsidies to animal carbon inferred from stable isotope composition did not differ between freshwater and terrestrial ecosystems, likely due to the differences in subsidy quality. The contribution of allochthonous subsidies was highest to primary consumers and predators, suggesting that bottom-up and top-down effects may be affected considerably by the input of allochthonous resources. Future work on subsidies will profit from a food web dynamic approach including indirect trophic interactions and propagating effects.

  • 3.
    Bejarano, Maria D.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Maroto, Judit
    Department of Forest Engineering, Technical University of Madrid, Madrid, Spain.
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Aguiar, Francisca Constança
    Centro de Estudos Florestais, Instituto Superior de Agronomia, Universidade de Lisboa, Lisboa, Portugal; CE3c – Centre for Ecology, Evolution and Environmental Changes, Faculdade de Ciências, Universidade de Lisboa, Lisboa, Portugal.
    Traits of riparian woody plants responding to hydrological and hydraulic conditions: A Northern Swedish database2016In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 97, no 10, p. 2892-2892Article in journal (Refereed)
    Abstract [en]

    The main goal of this study was to create a database that ultimately serves further studies on riparian vegetation and flow response guilds in the boreal region and on transferability of results across different regions. To achieve this aim, we compiled traits for all woody riparian species in northern Sweden which, directly or indirectly, underlie their responses to hydrological and hydraulic conditions, between October 2012 and April 2015. Consulted sources of information were diverse, ranging from scientific to informative and whose accuracy might or might not be verified. They were focused on particular or several traits and species from concrete areas to a worldwide perspective. Sources were characterized by different degrees of accessibility and showed a wide variety of descriptions, categorical and ordinal classifications, and numerical information for each trait. Our effort was to synthesize information for each trait from all sources into the common frame of our own database, following own defined criteria so that comparisons between species are congruent. Therefore, this data set is unique in that it comprehensively combines and homogenizes morphological, phenological, reproductive, and ecological data for 59 woody, riparian, boreal species and from 118 sources of information, that would otherwise be scattered and hardly available.

  • 4.
    Brodin, T
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Johansson, F
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Conflicting selection pressures on the growth /predation trade-off in a damselfly larvae2004In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 85, p. 2927-2932Article in journal (Refereed)
    Abstract [en]

    Activity is an important behavioral trait that in most animals mediates a trade-off between obtaining food for growth and avoiding predation. Active individuals usually experience a higher encounter rate with food items and predators and, as a consequence, grow faster and suffer higher predation pressure than less active individuals. We investigated how predator-induced mortality and growth of the damselfly Coenagrion hastulatum depend on activity at the level of the genotype. Larvae from six different C. hastulatum families were reared in two different predator treatments: predator present or absent. Families differed in activity, and active families grew to a significantly larger size than less-active families. Within families there was a plastic response to predators. Larvae reared without predators were more active and grew larger than larvae reared with a nonlethal predator. In the presence of a lethal predator the active families experienced higher mortality than the less active families. The results illustrate that the growth/predation-risk trade-off was mediated by activity and clearly show a cost of antipredator behavior. They also suggest that variation in activity level might be genetically regulated and could explain why C. hastulatum are abundant in aquatic systems both with and without potential predators.

  • 5.
    Brodin, Tomas
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Johansson, Frank
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Conflicting selection pressures on the growth/predation risk trade-off in a damselfly2004In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 85, no 11, p. 2927-2932Article in journal (Refereed)
    Abstract [en]

    Activity is an important behavioral trait that in most animals mediates a trade-off between obtaining food for growth and avoiding predation. Active individuals usually experience a higher encounter rate with food items and predators and, as a consequence, grow faster and suffer higher predation pressure than less active individuals. We investigated how predator-induced mortality and growth of the damselfly Coenagrion hastulatum depend on activity at the level of the genotype. Larvae from six different C. hastulatum families were reared in two different predator treatments: predator present or absent. Families differed in activity, and active families grew to a significantly larger size than less-active families. Within families there was a plastic response to predators. Larvae reared without predators were more active and grew larger than larvae reared with a nonlethal predator. In the presence of a lethal predator the active families experienced higher mortality than the less active families. The results illustrate that the growth/predation-risk trade-off was mediated by activity and clearly show a cost of antipredator behavior. They also suggest that variation in activity level might be genetically regulated and could explain why C. hastulatum are abundant in aquatic systems both with and without potential predators.

  • 6.
    Deininger, Anne
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Faithfull, Carolyn L.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Bergström, Ann-Kristin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Phytoplankton response to whole lake inorganic N fertilization along a gradient in dissolved organic carbon2017In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 98, no 4, p. 982-994Article in journal (Refereed)
    Abstract [en]

    Global change has increased inorganic nitrogen (N) and dissolved organic carbon (DOC; i.e. ‘browning’) inputs to northern hemisphere boreal lakes. However, we do not know how phytoplankton in nutrient poor lake ecosystems of different DOC concentration respond to increased N availability. Here, we monitored changes in phytoplankton production, biomass and community composition in response to whole lake inorganic N fertilization in six boreal unproductive Swedish lakes divided into three lake pairs (control, N enriched) at three DOC levels (low, medium, high), with one reference year (2011) and two impact years (2012, 2013). We found that phytoplankton biomass and production decreased with DOC concentration before N fertilization. Further, phytoplankton community composition also differed with respect to DOC, with a dominance of non-flagellated autotrophs at low DOC towards an increasing dominance of flagellated autotrophs with increased lake DOC concentration. The N fertilization increased phytoplankton biomass and production in all lakes, but did not affect phytoplankton community composition. However, the net response in biomass and production to N fertilization declined with increasing DOC, implying that the lake DOC concentration is critical in order to infer phytoplankton responses to N fertilization, and that the system switches from being primarily nutrient limited to becoming increasingly light limited with increased DOC concentration. In conclusion, our results show that browning will reduce phytoplankton production and biomass and influence phytoplankton community composition, whereas increased inorganic N loadings from deposition, forestry or other land use will primarily enhance phytoplankton biomass and production. Together, any change in the landscape that enhances inorganic N availability will increase phytoplankton production and biomass, but the positive effects of N will be much weaker or even neutralized in browner lakes as caused by light limitation.

  • 7.
    Diehl, Sebastian
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Department Biologie II, Ludwig-Maximilians-Universität München,Planegg, Germany.
    Berger, Stella
    Department Biologie II, Ludwig-Maximilians-Universität München,Planegg, Germany; Department of Experimental Limnology,Leibniz Institute of Freshwater Ecologyand Inland Fisheries (IGB), Stechlin,Germany.
    Uszko, Wojciech
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Department of Experimental Limnology,Leibniz Institute of Freshwater Ecologyand Inland Fisheries (IGB), Stechlin,Germany.
    Stibor, Herwig
    Department Biologie II, Ludwig-Maximilians-Universität München,Planegg, Germany.
    Stoichiometric mismatch causes a warming-induced regime shift in experimental plankton communities2022In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, article id e3674Article in journal (Refereed)
    Abstract [en]

    In many ecosystems, consumers respond to warming differently than their resources, sometimes leading to temporal mismatches between seasonal maxima in consumer demand and resource availability. A potentially equally pervasive, but less acknowledged threat to the temporal coherence of consumer-resource interactions is mismatch in food quality. Many plant and algal communities respond to warming with shifts toward more carbon-rich species and growth forms, thereby diluting essential elements in their biomass and intensifying the stoichiometric mismatch with herbivore nutrient requirements. Here we report on a mesocosm experiment on the spring succession of an assembled plankton community in which we manipulated temperature (ambient vs. +3.6°C) and presence versus absence of two types of grazers (ciliates and Daphnia), and where warming caused a dramatic regime shift that coincided with extreme stoichiometric mismatch. At ambient temperatures, a typical spring succession developed, where a moderate bloom of nutritionally adequate phytoplankton was grazed down to a clear-water phase by a developing Daphnia population. While warming accelerated initial Daphnia population growth, it speeded up algal growth rates even more, triggering a massive phytoplankton bloom of poor food quality. Consistent with the predictions of a stoichiometric producer–grazer model, accelerated phytoplankton growth promoted the emergence of an alternative system attractor, where the extremely low phosphorus content of the abundant algal food eventually drove Daphnia to extinction. Where present, ciliates slowed down the phytoplankton bloom and the deterioration of its nutritional value, but this only delayed the regime shift. Eventually, phytoplankton also grew out of grazer control in the presence of ciliates, and the Daphnia population crashed. To our knowledge, the experiment is the first empirical demonstration of the “paradox of energy enrichment” (grazer starvation in an abundance of energy-rich but nutritionally imbalanced food) in a multispecies phytoplankton community. More generally, our results support the notion that warming can exacerbate the stoichiometric mismatch at the plant–herbivore interface and limit energy transfer to higher trophic levels.

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  • 8.
    Dynesius, Mats
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Stockholms universitet, Botaniska institutionen.
    Hylander, Kristoffer
    Stockholms universitet, Botaniska institutionen.
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    High resilience of bryophyte assemblages in streamside compared to upland forests2009In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 90, no 4, p. 1042-1054Article in journal (Refereed)
    Abstract [en]

    Landscape heterogeneity causes spatial variation in disturbance regimes and resilience. We asked whether the resilience of bryophyte (liverwort and moss) assemblages to clear-cutting differs between streamside and upland boreal forests in northern Sweden. We hypothesized that bryophyte survival and recolonization rates are higher in streamside areas, thus raising resilience. Conversely, disturbance-intolerant but also invading species should be more frequent here, potentially reducing resilience. In each of 18 sites, we compared two 0.1-ha plots (one streamside and one upland) located in old forest that had never been clear-cut with two matching plots in young stands established after clear-cutting of old forests 30-50 years earlier. We used the magnitude of the difference in assemblages between old and young stands as a measure of change and, therefore, resilience (large difference implying low resilience). Species assemblages were more resilient in streamside than in upland forests. Species composition changed significantly in upland but not in streamside forests. Reductions in species richness were more pronounced in upland forests for total richness and for eight subgroups of species. Two results indicated lower survival/recolonization in upland forests: (1) species had a stronger association with old stands in upland areas, and (2) among species present in both the old streamside and old upland plot in a site, fewer appeared in the young upland than in the corresponding streamside plot. Simultaneously, a higher proportion of species invaded streamside areas; 40 of the 262 species encountered in streamside forests increased their occupancy by two or more sites compared to only two of 134 species in uplands. We suggest that in boreal forests spatial variation in resilience of assemblages of forest organisms intolerant of canopy removal is related to factors governed mainly by topography. More generally, we argue that landscape-scale variation in resilience of assemblages is influenced by spatial variation in (1) stress and resource availability, (2) number of  disturbance intolerant species, and (3) magnitude of environmental changes brought about by a disturbance with a specific intensity. We also suggest that rapid recovery in the short term does not necessarily imply higher long-term ability to return to the pre-disturbance state.

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    High resilience of bryophyte assemblages in streamside compared to upland forests
  • 9. Farber, Leonie
    et al.
    Solhaug, Knut Asbjorn
    Esseen, Per-Anders
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Bilger, Wolfgang
    Gauslaa, Yngvar
    Sunscreening fungal pigments influence the vertical gradient of pendulous lichens in boreal forest canopies2014In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 95, no 6, p. 1464-1471Article in journal (Refereed)
    Abstract [en]

    Pendulous lichens dominate canopies of boreal forests, with dark Bryoria species in the upper canopy vs. light Alectoria and Usnea species in lower canopy. These genera offer important ecosystem services such as winter forage for reindeer and caribou. The mechanism behind this niche separation is poorly understood. We tested the hypothesis that species-specific sunscreening fungal pigments protect underlying symbiotic algae differently against high light, and thus shape the vertical canopy gradient of epiphytes. Three pale species with the reflecting pigment usnic acid (Alectoria sarmentosa, Usnea dasypoga, U. longissima) and three with dark, absorbing melanins (Bryoria capillaris, B. fremontii, B. fuscescens) were compared. We subjected the lichens to desiccation stress with and without light, and assessed their performance with chlorophyll fluorescence. Desiccation alone only affected U. longissima. By contrast, light in combination with desiccation caused photoinhibitory damage in all species. Usnic lichens were significantly more susceptible to light during desiccation than melanic ones. Thus, melanin is a more efficient light-screening pigment than usnic acid. Thereby, the vertical gradient of pendulous lichens in forest canopies is consistent with a shift in type and functioning of sunscreening pigments, from high-light-tolerant Bryoria in the upper to susceptible Alectoria and Usnea in the lower canopy.

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  • 10.
    Frainer, André
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Department of Aquatic Ecology, Eawag: Swiss Federal Institute of Aquatic Science and Technology, Dübendorf, Switzerland ; Institute of Integrative Biology (IBZ), ETH Zurich, Zurich, Switzerland ; epartment of Ecology, Federal University of Rio Grande do Sul, Porto Alegre, Brazil ; Department of Arctic and Marine Biology, University of Tromsø, Tromsø, Norway.
    Moretti, Marcelo S
    Xu, Wenjing
    Gessner, Mark O
    No evidence for leaf-trait dissimilarity effects on litter decomposition, fungal decomposers, and nutrient dynamics2015In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 96, no 2, p. 550-561Article in journal (Refereed)
    Abstract [en]

    Biodiversity and ecosystem-functioning theory suggest that litter mixtures composed of dissimilar leaf species can enhance decomposition due to species trait complementarity. Here we created a continuous gradient of litter chemistry trait variability within species mixtures to assess effects of litter dissimilarity on three related processes in a natural stream: litter decomposition, fungal biomass accrual in the litter, and nitrogen and phosphorus immobilization. Litter from a pool of eight leaf species was analyzed for chemistry traits affecting decomposition (lignin, nitrogen, and phosphorus) and assembled in all of the 28 possible two-species combinations. Litter dissimilarity was characterized in terms of a range of trait-diversity measures, using Euclidean and Gower distances and dendrogram-based indices. We found large differences in decomposition rates among leaf species, but no significant relationships between decomposition rate of individual leaf species and litter trait dissimilarity, irrespective of whether decomposition was mediated by microbes alone or by both microbes and litter-consuming invertebrates. Likewise, no effects of trait dissimilarity emerged on either fungal biomass accrual or changes during decomposition of nitrogen or phosphorus concentrations in individual leaf species. In line with recent meta-analyses, these results provide support for the contention that litter diversity effects on decomposition, at least in streams, are less pronounced than effects on terrestrial primary productivity.

  • 11. Grosbois, Guillaume
    et al.
    Vachon, Dominic
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    del Giorgio, Paul A.
    Rautio, Milla
    Efficiency of crustacean zooplankton in transferring allochthonous carbon in a boreal lake2020In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 101, no 6, article id e03013Article in journal (Refereed)
    Abstract [en]

    Increased incorporation of terrestrial organic matter (t-OM) into consumer biomass (allochthony) is believed to reduce growth capacity. In this study, we examined the relationship between crustacean zooplankton allochthony and production in a boreal lake that displays strong seasonal variability in t-OM inputs. Contrary to our hypotheses, we found no effect of allochthony on production at the community and the species levels. The high-frequency seasonal sampling (time-for-space) allowed for estimating the efficiency of zooplankton in converting this external carbon source to growth. From the daily t-OM inputs in the lake (57-3,027 kg C/d), the zooplankton community transferred 0.2% into biomass (0.01-2.36 kg C/d); this level was of the same magnitude as the carbon transfer efficiency for algal-derived carbon (0.4%). In the context of the boundless carbon cycle, which integrates inland waters as a biologically active component of the terrestrial landscape, the use of the time-for-space approach for the quantifying of t-OM trophic transfer efficiency by zooplankton is a critical step toward a better understanding of the effects of increasing external carbon fluxes on pelagic food webs.

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  • 12. Hambäck, PA
    et al.
    Agren, J
    Ericson, L
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Associational resistance: Insect damage to purple loosestrife reduced in thickets of sweet gale2000In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 81, no 7, p. 1784-1794Article in journal (Refereed)
  • 13. Hasselquist, Niles J.
    et al.
    Metcalfe, Daniel B.
    Inselsbacher, Erich
    Stangl, Zsofia
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC). Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Oren, Ram
    Näsholm, Torgny
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC). Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, SE-901 83, Umeå, Sweden.
    Högberg, Peter
    Greater carbon allocation to mycorrhizal fungi reduces tree nitrogen uptake in a boreal forest2016In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 97, no 4, p. 1012-1022Article in journal (Refereed)
    Abstract [en]

    The central role that ectomycorrhizal (EM) symbioses play in the structure and function of boreal forests pivots around the common assumption that carbon (C) and nitrogen (N) are exchanged at rates favorable for plant growth. However, this may not always be the case. It has been hypothesized that the benefits mycorrhizal fungi convey to their host plants strongly depends upon the availability of C and N, both of which are rapidly changing as a result of intensified human land use and climate change. Using large-scale shading and N addition treatments, we assessed the independent and interactive effects of changes in C and N supply on the transfer of N in intact EM associations with similar to 15 yr. old Scots pine trees. To assess the dynamics of N transfer in EM symbioses, we added trace amounts of highly enriched (NO3-)-N-15 label to the EM-dominated mor-layer and followed the fate of the N-15 label in tree foliage, fungal chitin on EM root tips, and EM sporocarps. Despite no change in leaf biomass, shading resulted in reduced tree C uptake, ca. 40% lower fungal biomass on EM root tips, and greater N-15 label in tree foliage compared to unshaded control plots, where more N-15 label was found in fungal biomass on EM colonized root tips. Short-term addition of N shifted the incorporation of N-15 label from EM fungi to tree foliage, despite no significant changes in below-ground tree C allocation to EM fungi. Contrary to the common assumption that C and N are exchanged at rates favorable for plant growth, our results show for the first time that under N-limited conditions greater C allocation to EM fungi in the field results in reduced, not increased, N transfer to host trees. Moreover, given the ubiquitous nature of mycorrhizal symbioses, our results stress the need to incorporate mycorrhizal dynamics into process-based ecosystem models to better predict forest C and N cycles in light of global climate change.

  • 14.
    Henriksson, Anna
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Rydberg, Cecilia
    Umeå University, Faculty of Science and Technology, Department of Mathematics and Mathematical Statistics.
    Englund, Göran
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Failed and successful intentional introductions of fish species into 821 Swedish lakes2016In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 97, no 5, p. 1p. 1364-1364Article in journal (Refereed)
    Abstract [en]

    Introductions of fish into lakes can be viewed as whole system experiments, which can be used to study the principles of community assembly and factors determining the outcome of species invasions. Freshwater fish species have been translocated by humans for centuries in Sweden, and this activity has been documented by national and regional authorities starting at the end of the 19th century. Based on this documentation and additional interviews with local fishermen, we have compiled a data set that includes 1157 intentional introductions of 26 freshwater fish species into 821 Swedish lakes. The data include both successful and failed introductions; where a successful introduction means that the introduced fish species was present in the lake for ≥20 yr or that reproduction was observed earlier than that. The oldest introduction is from 1658 and the latest from 2002. Additionally, the data set includes species composition, water temperature sum, maximum water temperature, lake area, elevation, longitude, and latitude for all lakes. These data have been used to test hypotheses about biotic resistance and invasion success in three papers. We found the presence or absence of specific species predicted invasion success better than the species richness of the lakes. We also found that species with high invasion success tend to make a large contribution to biotic resistance, which will make communities more resistant in the future as they are invaded by additional species.

  • 15.
    Henriksson, Anna
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Yu, Jun
    Umeå University, Faculty of Science and Technology, Department of Mathematics and Mathematical Statistics.
    Wardle A., David
    Swedish University of Agriculture Sciences, Department of Forest Vegetation Ecology.
    Trygg, Johan
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Englund, Göran
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Weighted species richness outperforms species richness as predictor of biotic resistance2016In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 97, no 1, p. 262-271Article in journal (Refereed)
    Abstract [en]

    The species richness hypothesis, which predicts that species-rich communities should be better at resisting invasions than species-poor communities, has been empirically tested many times and often poorly supported. In this paper we contrast the species richness hypothesis with four alternative hypotheses with the aim of finding better descriptors of invasion resistance. These alternative hypotheses state that resistance to invasions is determined by abiotic conditions, community saturation (i.e., the number of resident species relative to the maximum number of species that can be supported), presence/absence of key species, or weighted species richness. Weighted species richness is a weighted sum of the number of species, where each species' weight describes its contribution to resistance. We tested these hypotheses using data on the success of 571 introductions of four freshwater fish species into lakes throughout Sweden (i.e., Arctic char (Salvelinus alpinus), tench (Tinca tinca), zander (Sander lucioperca), and whitefish (Coregonus lavaretus)). We found that the weighted species richness best predicted invasion success. The weights describing the contribution of each resident species to community resistance varied considerably in both strength and sign. Positive resistance weights, which indicate that species repel invaders, were as common as negative resistance weights, which indicate facilitative interactions. This result can be contrasted with the implicit assumption of the original species richness hypothesis, that all resident species have negative effects on invader success. We argue that this assumption is unlikely to be true in natural communities, and thus that we expect that weighted species richness is a better predictor of invader success than the actual number of resident species.

  • 16.
    Hotchkiss, Erin R.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Hall, Robert O.
    Program in Ecology, Department of Zoology and Physiology, University of Wyoming, United States.
    Whole-stream 13C tracer addition reveals distinct fates of newly fixed carbon2015In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 96, no 2, p. 403-416Article in journal (Refereed)
    Abstract [en]

    Many estimates of freshwater carbon (C) fluxes focus on inputs, processing, and storage of terrestrial C; yet inland waters have high rates of internally fixed (autochthonous) C production. Some fraction of newly fixed C may be released as biologically available, dissolved organic C (DOC) and stimulate microbial-driven biogeochemical cycles soon after fixation, but the fate of autochthonous C is difficult to measure directly. Tracing newly fixed C can increase our understanding of fluxes and fate of autochthonous C in the context of freshwater food webs and C cycling. We traced autochthonous C fixation and fate using a dissolved inorganic C stable isotope addition (13CDIC). We added 13CDIC to North Fork French Creek, Wyoming, USA during two days in August. We monitored changes in 13C pools, fluxes, and storage for 44 d after the addition. Two-compartment flux models were used to quantify net release of newly fixed 13CDOC and 13CDIC into the water column. We compared net 13C fixation with tracer 13CDIC removal and gross primary production (GPP) to account for the mass of tracer fixed, released, lost to the atmosphere, and exported downstream. Much of the fixed C turned over rapidly and did not enter longer-term storage pools. Net C fixed was 70% of GPP measured with O2. Algae likely released the remaining 30% via 13CDOC exudation and respiration of newly fixed C. Primary producers released 13CDOC at rates of up to 16% per day during the 13C addition, but exudation of new labile C declined to near zero by day 6. DIC production from newly fixed C accounted for 21% of ecosystem respiration the day after the 13C addition. All measured organic C (OC) pools were enriched with 13C 1 d after the tracer addition. 20% of fixed 13C remained in benthic OC by day 44, and average residence time of autochthonous C in benthic OC was 62 d. Newly fixed C had two distinct fates: short-term (<1 week) exudation and respiration or longer-term storage and downstream export. Autochthonous C in streams likely fuels short-term microbial production and biogeochemical cycling, in addition to providing a longer-term resource for consumers.

  • 17.
    Jansson, Mats
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Bergström, Ann-Kristin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Blomqvist, Peter
    Drakare, Stina
    Allochthonous organic carbon and phytoplankton/bacterioplankton production relationships in lakes2000In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 81, no 11, p. 3250-3255Article in journal (Refereed)
    Abstract [en]

    Humic lakes with high inputs of allochthonous dissolved organic carbon have a pelagic food chain that, to a large extent, is based on bacterioplankton energy mobilization from allochthonous organic carbon compounds. This is in contrast to clear lakes in which total pelagic production is based mainly on phytoplankton photosynthesis. The energy economy in humic lakes may be less efficient than in clear lakes, because it is Likely that one more link is included in the food chain. Lake data from Scandinavia and North America demonstrate that shifts between food chains based on heterotrophic production and food chains based on primary production can take place at moderate increases or decreases in the concentration of dissolved organic carbon from allochthonous sources. Large variations in the loading of allochthonous organic carbon (e.g., due to climatic variations) may have considerable effects on the biostructure and productivity of lakes.

  • 18.
    Jonsson, Hanna
    et al.
    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.
    Blume-Werry, Gesche
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Klaminder, Jonatan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Cascading effects of earthworm invasion increase graminoid density and rodent grazing intensities2024In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 105, no 2, article id e4212Article in journal (Refereed)
    Abstract [en]

    Human-mediated dispersal of non-native earthworms can cause substantial changes to the functioning and composition of ecosystems previously earthworm-free. Some of these earthworm species have the potential to “geoengineer” soils and increase plant nitrogen (N) uptake. Yet the possible consequences of increased plant N concentrations on rodent grazing remains poorly understood. In this study, we present findings from a common garden experiment with two tundra communities, meadow (forb dominated) and heath (shrub dominated), half of them subjected to 4 years of earthworm presence (Lumbricus spp. and Aporrectodea spp.). Within four summers, our earthworm treatment changed plant community composition by increasing graminoid density by, on average, 94% in the heath vegetation and by 49% in the meadow. Rodent winter grazing was more intense on plants growing in soils with earthworms, an effect that coincided with higher N concentrations in plants, indicating a higher palatability. Even though earthworms reduced soil moisture, plant community productivity, as indicated by vegetation greenness (normalized difference vegetation index), was not negatively impacted. We conclude that earthworm-induced changes in plant composition and trophic interactions may fundamentally alter the functioning of tundra ecosystems.

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  • 19.
    Karlsson, Jan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Bergström, Ann-Kristin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Byström, Pär
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Gudasz, Cristian
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Rodriguez, Patricia
    Hein, Catherine
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Terrestrial organic matter input suppresses biomass production in lake ecosystems2015In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 96, no 11, p. 2870-2876Article in journal (Refereed)
    Abstract [en]

    Terrestrial ecosystems export large amounts of organic carbon (t-OC) but the net effect of this OC on the productivity of recipient aquatic ecosystems is largely unknown. In this study of boreal lakes, we show that the relative contribution of t-OC to individual top consumer (fish) biomass production, and to most of their potential prey organisms, increased with the concentration of dissolved organic carbon (DOC; dominated by t-OC sources) in water. However, the biomass and production of top consumers decreased with increasing concentration of DOC, despite their substantial use (up to 60%) of t-OC. Thus, the results suggest that although t-OC supports individual consumer growth in lakes to a large extent, t-OC input suppresses rather than subsidizes population biomass production.

  • 20.
    Karlsson, Jan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jansson, Mats
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jonsson, Anders
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Similar relationships between pelagic primary and bacterial production in clearwater and humic lakes2002In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 83, no 10, p. 2902-2910Article in journal (Refereed)
    Abstract [en]

    We examined the relationship between planktonic primary production (PP) and bacterial production (BP) in 16 subarctic lakes along an altitude gradient extending from colored coniferous forest lakes to clearwater high alpine lakes. We tested the hypothesis that there was a shift from low to high PP:BP ratios along this gradient. The clearwater alpine lakes had low PP:BP ratios, generally well below 1.0, while the highest ratios were-found in the forest lakes. In contradiction to our hypothesis, the pelagic systems of the clearwater lakes were thus dominated by bacterial energy mobilization from external carbon sources. In this respect the alpine lakes were similar to highly humic lakes. We suggest that the relationship between C, N, and P plays a critical role in determining the PP:BP ratio, and that the N:P ratio in particular can be critical for development of PP or BP dominance in the pelagic systems of unproductive lakes.

  • 21.
    Kuglerova, Lenka
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jansson, Roland
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Ågren, Anneli
    Laudon, Hjalmar
    Malm-Renöfält, Birgitta
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Groundwater discharge creates hotspots of riparian plant species richness in a boreal forest stream network2014In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 95, no 3, p. 715-725Article in journal (Refereed)
    Abstract [en]

    Riparian vegetation research has traditionally focused on channel-related processes because riparian areas are situated on the edge of aquatic ecosystems and are therefore greatly affected by the flow regime of streams and rivers. However, due to their low topographic position in the landscape, riparian areas receive significant inputs of water and nutrients from uplands. These inputs may be important for riparian vegetation, but their role for riparian plant diversity is poorly known. We studied the relationship between the influx of groundwater (GW) from upland areas and riparian plant diversity and composition along a stream size gradient, ranging from small basins lacking permanent streams to a seventh-order river in northern Sweden. We selected riparian sites with and without GW discharge using a hydrological model describing GW flow accumulation to test the hypothesis that riparian sites with GW discharge harbor plant communities with higher species richness. We further investigated several environmental factors to detect habitat differences between sites differing in GW discharge conditions. Vascular plant species richness was between 15% and 20% higher, depending on the spatial scale sampled, at riparian sites with GW discharge in comparison to non-discharge sites, a pattern that was consistent across all stream sizes. The elevated species richness was best explained by higher soil pH and higher nitrogen availability (manifested as lower soil C/N ratio), conditions which were positively correlated with GW discharge. Base cations and possibly nitrogen transported by groundwater may therefore act as a terrestrial subsidy of riparian vegetation. The stable isotopes N-15 and C-13 were depleted in soils from GW discharge compared to non-discharge sites, suggesting that GW inputs might also affect nitrogen and carbon dynamics in riparian soils. Despite the fact that many flows of water and nutrients reaching streams are filtered through riparian zones, the importance of these flows for riparian vegetation has not been appreciated. Our results demonstrated strong relationships between GW discharge, plant species richness and environmental conditions across the entire stream size gradient, suggesting that both river hydrology and upland inputs should be considered to fully understand riparian vegetation dynamics.

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  • 22.
    Kuglerová, Lenka
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jansson, Roland
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Sponseller, Ryan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Laudon, Hjalmar
    Sveriges lantbruksuniversitet.
    Malm-Renöfält, Birgitta
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Local and regional processes determine plant species richness in a river-network metacommunity2015In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 96, no 2, p. 381-391Article in journal (Refereed)
    Abstract [en]

    River systems form dendritic ecological networks that influence the spatial structure of riverine communities. Few empirical studies have evaluated how regional, dispersal-related processes and local habitat factors interact to govern network patterns of species composition. We explore such interactions in a boreal watershed and show that riparian plant species richness increases strongly with drainage size, i.e., with downstream position in the network. Assemblage composition was nested, with new species successively added downstream. These spatial patterns in species composition were related to a combination of local and regional processes. Breadth in local habitat conditions increased downstream in the network, resulting in higher habitat heterogeneity and reduced niche overlap among species, which together with similar trends in disturbance, allows more species to coexist. Riparian edaphic conditions were also increasingly favorable to more species within the regional pool along larger streams, with greater nitrogen availability (manifested as lower C:N) and more rapid mineralization of C and N (as indicated by ratios of stable isotopes) observed with downstream position in the network. The number of species with capacity for water dispersal increased with stream size providing a mechanistic link between plant traits and the downstream accumulation of species as more propagules arrive from upstream sites. Similarity in species composition between sites was related to both geographical and environmental distance. Our results provide the first empirical evidence that position in the river network drives spatial patterns in riparian plant diversity and composition by the joint influence of local (disturbance, habitat conditions, and breadth) and regional (dispersal) forces.

  • 23.
    Nilsson-Örtman, Viktor
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Stoks, Robby
    De Block, Marjan
    Johansson, Frank
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Generalists and specialists along a latitudinal transect: patterns of thermal adaptation in six species of damselflies2012In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 93, no 6, p. 1340-1352Article in journal (Refereed)
    Abstract [en]

    Tropical organisms colonizing temperate environments face reduced average temperatures and dramatic thermal fluctuations. Theoretical models postulate that thermal specialization should be favored either when little environmental variation is experienced within generations or when among-generation variation is small relative to within-generation variation. To test these predictions, we studied six temperate species of damselflies differing in latitudinal distribution. We developed a computer model simulating how organisms experience environmental variation (accounting for diapause and voltinism) and performed a laboratory experiment assaying thermal sensitivities of growth rates. The computer model showed opposing latitudinal trends in among-and within-generation thermal variability: within-generation thermal variability decreased toward higher latitudes, whereas relative levels of among-generation thermal variability peaked at midlatitudes (where a shift in voltinism occurred). The growth experiment showed that low-latitude species were more thermally generalized than mid- and high-latitude species, supporting the prediction that generalists are favored under high levels of within-generation variation. Northern species had steeper, near-exponential reaction norms suggestive of thermal specialization. However, they had strikingly high thermal optima and grew very slowly over most of the thermal range they are expected to experience in the field. This observation is at present difficult to explain. These results highlight the importance of considering interactions between life history and environmental variation when deriving expectations of thermal adaptation.

  • 24.
    Nilsson-Örtman, Viktor
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Stoks, Robby
    Johansson, Frank
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Competitive interactions modify the temperature dependence of damselfly growth rates2014In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 95, no 5, p. 1394-1406Article in journal (Refereed)
    Abstract [en]

    Individual growth rates and survival are major determinants of individual fitness, population size structure, and community dynamics. The relationships between growth rate, survival, and temperature may thus be important for predicting biological responses to climate change. Although it is well known that growth rates and survival are affected by competition and predation in addition to temperature, the combined effect of these factors on growth rates, survival, and size structure has rarely been investigated simultaneously in the same ecological system. To address this question, we conducted experiments on the larvae of two species of damselflies and determined the temperature dependence of growth rate, survival, and cohort size structure under three scenarios of increasing ecological complexity: no competition, intraspecific competition, and interspecific competition. In one species, the relationship between growth rate and temperature became steeper in the presence of competitors, whereas that of survival remained unchanged. In the other species, the relationship between growth rate and temperature was unaffected by competitive interactions, but survival was greatly reduced at high temperatures in the presence of interspecific competitors. The combined effect of competitive interactions and temperature on cohort size structure differed from the effects of these factors in isolation. Together, these findings suggest that it will be challenging to scale up information from single-species laboratory studies to the population and community level.

  • 25.
    Persson, Lennart
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    de Roos, Andre M
    Symmetry breaking in ecological systems through different energy efficiencies of juveniles and adults2013In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 94, no 7, p. 1487-1498Article in journal (Refereed)
    Abstract [en]

    Ontogenetic development is a fundamental aspect of the life history of all organisms and has major effects on population and community dynamics. We postulate a general conceptual framework for understanding these effects and claim that two potential energetics bottlenecks at the level of the individual organismthe rate by which it develops and the rate by which it reproducesform a fundamental route to symmetry-breaking in ecological systems, leading to ontogenetic asymmetry in energetics. Unstructured ecological theory, which ignores ontogenetic development, corresponds to a limiting case only, in which mass-specific rates of biomass production through somatic growth and reproduction, and biomass loss through mortality, are independent of body size (ontogenetic symmetry). Ontogenetic symmetry results in development and reproduction being limited to the same extent by food density. In all other cases, symmetry-breaking occurs. Ontogenetic asymmetry results in increases in juvenile, adult, or even total biomass in response to mortality. At the community level, this gives rise to alternative stable states via predator-induced shifts in prey size distributions. Ontogenetic asymmetry furthermore leads to two distinct types of cycles in population dynamics, depending on whether development or reproduction is most energy limited. We discuss the mechanisms giving rise to these phenomena and the empirical support for them. We conclude that the concepts of ontogenetic symmetry and ontogenetic asymmetry form a novel and general organizing principle on which future ecological theory should be developed.

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  • 26.
    Robbins, Caleb J.
    et al.
    Department of Biology, Center for Reservoir and Aquatic Systems Research, Baylor University, TX, Waco, United States.
    Manning, David W. P.
    Department of Biology, University of Nebraska at Omaha, NE, Omaha, United States.
    Halvorson, Halvor M.
    Department of Biology, University of Central Arkansas, AR, Conway, United States.
    Norman, Beth C.
    Lacawac Sanctuary Field Station and Environmental Education Center, PA, Lake Ariel, United States.
    Eckert, Rebecca A.
    Biology Department, Environmental Studies Department, Gettysburg College, PA, Gettysburg, United States.
    Pastor, Ada
    Group of Continental Aquatic Ecology Research (GRECO), Institute of Aquatic Ecology, University of Girona, Girona, Spain.
    Dodd, Allyn K.
    Arkansas School for Math, Sciences, and the Arts, AR, Hot Springs, United States.
    Jabiol, Jérémy
    HYFE—Hydrobiologie et Fonctionnement des Ecosystèmes, Elven, France.
    Bastias, Elliot
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Gossiaux, Alice
    University of Lorraine, Lorraine, France.
    Mehring, Andrew S.
    Department of Biology, University of Louisville, KY, Louisville, United States.
    Nutrient and stoichiometry dynamics of decomposing litter in stream ecosystems: a global synthesis2023In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 104, no 7, article id e4060Article in journal (Refereed)
    Abstract [en]

    Decomposing organic matter forms a substantial resource base, fueling the biogeochemical function and secondary production of most aquatic ecosystems. However, detrital N (nitrogen) and P (phosphorus) dynamics remain relatively unexplored in aquatic ecosystems relative to terrestrial ecosystems, despite fundamentally linking microbial processes to ecosystem function across broad spatial scales. We synthesized 217 published time series of detrital carbon (C), N, P, and their stoichiometric ratios (C:N, C:P, N:P) from stream ecosystems to analyze the temporal nutrient dynamics of decomposing litter using generalized additive models. Model results indicated that detritus was a net source of N (irrespective of inorganic or organic form) to the environment, regardless of initial N content. In contrast, P sink/source dynamics were more strongly influenced by the initial P content, in which P-poor litters were sinks for nutrients until these shifted to net P mineralization after ~40% mass loss. However, large variations surrounded both the N and P predictions, suggesting the importance of nonmicrobial factors such as fragmentation by invertebrates. Detrital C:N ratios converged and became more similar toward the end of the decomposition, suggesting predictable microbial functional effects throughout detrital ontogeny. C:P and N:P ratios also converged to some degree, but these model predictions were less robust than for C:N, due in part to the lower number of published detrital C:P time series. The explorations of environmental covariate effects were frequently limited by a few coincident covariate measurements across studies, but temperature, N availability, and P tended to accelerate the existing ontogenetic patterns in C:N. Our analysis helps to unite organic matter decomposition across aquatic–terrestrial boundaries by describing the basic patterns of elemental flows catalyzed by decomposition in streams, and points to a research agenda with which to continue addressing gaps in our knowledge of detrital nutrient dynamics across ecosystems.

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  • 27.
    Robbins, Caleb J.
    et al.
    Department of Biology, Center for Reservoir and Aquatic Systems Research, Baylor University, TX, Waco, United States.
    Norman, Beth C.
    Lacawac Sanctuary Biological Field Station and Environmental Education Center, PA, Lake Ariel, United States.
    Halvorson, Halvor M.
    Department of Biology, University of Central Arkansas, AR, Conway, United States.
    Manning, David W. P.
    Department of Biology, University of Nebraska–Omaha, NE, Omaha, United States.
    Bastias, Elliot
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Biasi, Cristiane
    Universidade Regional Integrada do Alto Uruguai e das Missões, Erechim, Brazil.
    Dodd, Allyn K.
    Arkansas School for Mathematics, Sciences, and the Arts, AR, Hot Springs, United States.
    Eckert, Rebecca A.
    Biology Department, Environmental Studies Department, Gettysburg College, PA, Gettysburg, United States.
    Gossiaux, Alice
    LIEC, Université de Lorraine, CNRS, Metz, France.
    Jabiol, Jérémy
    HYFE (Hydrobiologie Et Fonctionnement Des Ecosystèmes), Elven, France.
    Mehring, Andrew S.
    Department of Biology, University of Louisville, KY, Louisville, United States.
    Pastor, Ada
    Group of Continental Aquatic Ecology Research (GRECO), Institute of Aquatic Ecology, University of Girona, Girona, Spain.
    Nutrient and stoichiometric time series measurements of decomposing coarse detritus in freshwaters2023In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 104, no 8, article id e4114Article in journal (Refereed)
    Abstract [en]

    Decomposition of coarse detritus (e.g., dead organic matter larger than ~1 mm such as leaf litter or animal carcasses) in freshwater ecosystems is well described in terms of mass loss, particularly as rates that compress mass loss into one number (e.g., a first-order decay coefficient, or breakdown rate, “k”); less described are temporal changes in the elemental composition of these materials during decomposition, with important implications for elemental cycling from microbes to ecosystems. This stands in contrast with work in the terrestrial realm, where a focus on detrital elemental cycling has provided a sharper mechanistic understanding of decomposition, especially with specific processes such as immobilization and mineralization. Notably, freshwater ecologists often measure carbon (C), nitrogen (N), and phosphorus (P), and their stoichiometric ratios in decomposing coarse materials, including carcasses, wood, leaf litter, and more, but these measurements remain piecemeal. These detrital nutrients are measurements of the entire detrital–microbial complex and are integrative of numerous processes, especially nutrient immobilization and mineralization, and associated microbial growth and death. Thus, data relevant to an elemental, mechanistically focused decomposition ecology are available in freshwaters, but have not been fully applied to that purpose. We synthesized published detrital nutrient and stoichiometry measurements at a global scale, yielding 4038 observations comprising 810 decomposition time series (i.e., measurements within a defined cohort of decomposing material through time) to build a basis for understanding the temporality of elemental content in freshwater detritus. Specifically, the dataset focuses on temporally and ontogenetically (mass loss) explicit measurements of N, P, and stoichiometry (C:N, C:P, N:P). We also collected ancillary data, including detrital characteristics (e.g., species, lignin content), water physiochemistry, geographic location, incubation system type, and methodological variables (e.g., bag mesh size). These measurements are important to unlocking mechanistic insights into detrital ontogeny (the temporal trajectory of decomposing materials) that can provide a deeper understanding of heterotroph-driven C and nutrient cycling in freshwaters. Moreover, these data can help to bridge aquatic and terrestrial decomposition ecology, across plant or animal origin. By focusing on temporal trajectories of elements, this dataset facilitates cross-ecosystem comparisons of fundamental decomposition controls on elemental fluxes. It provides a strong starting point (e.g., via modeling efforts) for comparing processes such as immobilization and mineralization that are understudied in freshwaters. Time series from decomposing leaf litter, particularly in streams, are common in the dataset, but we also synthesized ontogenies of animal-based detritus, which tend to decompose rapidly compared with plant-based detritus that contains high concentrations of structural compounds such as lignin and cellulose. Although animal-based data were rare, comprising only three time series, their inclusion in this dataset underscores the opportunities to develop an understanding of decomposition that encompasses all detrital types, from carrion to leaf litter. There are no copyright or proprietary restrictions on the dataset; please cite this data paper when reusing these materials.

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  • 28.
    Soucémarianadin, Laure N.
    et al.
    Department of Renewable Resources, University of Alberta, Edmonton, Canada.
    Quideau, Sylvie A.
    Wasylishen, Roderick E.
    Munson, Alison D.
    Early-season fires in boreal black spruce forests produce pyrogenic carbon with low intrinsic recalcitrance2015In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 96, no 6, p. 1575-1585Article in journal (Refereed)
    Abstract [en]

    Pyrogenic carbon (PyC), a major by-product of wildfires in boreal forests, plays several critical roles in soil biogeochemical processes. However, PyC properties, including its potential recalcitrance, may vary depending on its formation conditions. Our study aimed to characterize the chemical and physical properties of PyC formed under variable fire severity in Eastern Canada boreal forests; these latter represent an important fraction of fire-affected circumboreal ecosystems. A total of 267 PyC samples, produced by early-season wildfires in 2005-2007, were collected <= 5 years after fire from the forest floors of 14 black spruce sites distributed across Quebec, to cover the range of fire severity encountered in these forests. Early-season fires occur frequently in Eastern Canada, and are predicted to increase in regional and global scenarios of future fire regimes associated with climate change. Selected PyC samples were analyzed using elemental analysis, solid-state C-13 nuclear magnetic resonance (NMR) spectroscopy, scanning electron microscopy, and surface area analysis. The NMR spectra of the PyC collected on low-fire-severity sites were dominated by peaks indicative of cellulose, while those for PyC from higher-severity sites were dominated by a broad peak assigned to aromatic carbons. Atomic H/C and O/C ratios decreased with increasing fire severity. By comparing field samples to samples produced in the laboratory under controlled formation conditions, we were able to infer that the temperature of formation in the field was low (75 degrees-250 degrees C). In addition, for all PyC samples, the aromatic carbon : total carbon ratio was small, suggesting that PyC produced by early-season fires in these boreal forests may be susceptible to relatively rapid degradation. Taken together, our data suggest that boreal PyC may not be as recalcitrant as previously assumed, and that its influence on soil biogeochemical processes may be short lived.

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  • 29. Stark, Sari
    et al.
    Egelkraut, Dagmar
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Aronsson, Kjell-Åke
    Olofsson, Johan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Contrasting vegetation states do not diverge in soil organic matter storage: evidence from historical sites in tundra2019In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 100, no 7, article id e02731Article in journal (Refereed)
    Abstract [en]

    Ecosystems where severe disturbance has induced permanent shifts in vegetation and soil processes may represent alternative stable states. To date, little is known on how long-lasting changes in soil processes are following such disturbances, and how the changes in plant and soil processes between the alternative states eventually manifest themselves in soil organic matter (SOM) storage. Here, we analyzed plant density, the shrub : forb ratio, microbial respiration, extracellular enzyme activities and SOM stocks in soils of subarctic tundra and historical milking grounds, where reindeer herding induced a vegetation transition from deciduous shrubs to graminoids several centuries earlier but were abandoned a century ago. This provides the possibility to compare sites with similar topography, but highly contrasting vegetation for centuries. We found that enzymatic activities and N:P stoichiometry differed between control and disturbed sites, confirming that culturally induced vegetation shifts exert lasting impacts on tundra soil processes. Transition zones, where shrubs had encroached into the historical milking grounds during the past 50 yr, indicated that microbial activities for N and P acquisition changed more rapidly along a vegetation shift than those for microbial C acquisition. Although plant and soil processes differed between control and disturbed sites, we found no effect of historical vegetation transition on SOM stock. Across the study sites, soil SOM stocks were correlated with total plant density but not with the shrub : forb ratio. Our finding that SOM stock was insensitive to a centennial difference in plant community composition suggests that, as such, grazing-induced alternative vegetation states might not necessarily differ in SOM sequestration.

  • 30.
    Stenberg, Johan A.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Hambäck, Peter A.
    Plant Ecology, Department of Botany, Stockholm University,Stockholm, Sweden.
    Ericson, Lars
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Herbivore-induced "rent rise" in the host plant may drive a diet breadth enlargement in the tenant2008In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 89, no 1, p. 126-133Article in journal (Refereed)
    Abstract [en]

    Inter- and intraspecies variations in host plant traits are presumably involved in many host shifts by insect herbivores, and elucidating the mechanisms involved in such shifts has been a crucial goal in insect-plant research for several decades. Here we propose that herbivore-induced evolutionary increases in host plant resistance may cause oligophagous insect herbivores to shift to other sympatric plants as currently preferred host plants become increasingly unpalatable. We tested this hypothesis in a system based on the perennial herb Filipendula uhnaria (Rosaceae), whose herbivory defense has become gradually stronger due to prolonged selection by Galerucella tenella (Coleoptera: Chrysomelidae) herbivory in a boreal archipelago. We. show that Galerucella gradually increases its use of the alternative host plant Rubus arcticus (Rosaceae) in parallel to gradually increased resistance in Filipendula. Our results imply that, by driving the evolutionary increase in Filipendula resistance, Galerucella is also gradually making the original host species more unpalatable and thereby driving its own host-breadth enlargement. We argue that such self-inflicted "rent rises" may be an important mechanism behind host plant shifts, which in turn are believed to have preceded the speciation of many phytophagous insects.

  • 31.
    Sundqvist, Maja K.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Swedish Univ Agr Sci, Dept Forest Ecol & Management, SE-90183 Umea, Sweden.
    Liu, Zhanfeng
    Chinese Acad Sci, South China Bot Garden, Key Lab Vegetat Restorat & Management Degraded Ec, Guangzhou 510650, Guangdong, Peoples R China.
    Giesler, Reiner
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Wardle, David A.
    Swedish Univ Agr Sci, Dept Forest Ecol & Management, SE-90183 Umea, Sweden.
    Plant and microbial responses to nitrogen and phosphorus addition across an elevational gradient in subarctic tundra2014In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 95, no 7, p. 1819-1835Article in journal (Refereed)
    Abstract [en]

    Temperature and nutrients are major limiting factors in subarctic tundra. Experimental manipulation of nutrient availability along elevational gradients (and thus temperature) can improve our understanding of ecological responses to climate change. However, no study to date has explored impacts of nutrient addition along a tundra elevational gradient, or across contrasting vegetation types along any elevational gradient. We set up a full factorial nitrogen (N) and phosphorus (P) fertilization experiment in each of two vegetation types (heath and meadow) at 500 m, 800 m, and 1000 m elevation in northern Swedish tundra. We predicted that plant and microbial communities in heath or at lower elevations would be more responsive to N addition while communities in meadow or at higher elevations would be more responsive to P addition, and that fertilizer effects would vary more with elevation for the heath than for the meadow. Although our results provided little support for these predictions, the relationship between nutrient limitation and elevation differed between vegetation types. Most plant and microbial properties were responsive to N and/or P fertilization, but responses often varied with elevation and/or vegetation type. For instance, vegetation density significantly increased with N + P fertilization relative to the other fertilizer treatments, and this increase was greatest at the lowest elevation for the heath but at the highest elevation for the meadow. Arbuscular mycorrhizae decreased with P fertilization at 500 m for the meadow, but with all fertilizer treatments in both vegetation types at 800 m. Fungal to bacterial ratios were enhanced by N + P fertilization for the two highest elevations in the meadow only. Additionally, microbial responses to fertilization were primarily direct rather than indirect via plant responses, pointing to a decoupled response of plant and microbial communities to nutrient addition and elevation. Because our study shows how two community types differ in their responses to fertilization and elevation, and because the temperature range across this gradient is similar to 3 degrees C, our study is informative about how nutrient limitation in tundra may be influenced by temperature shifts that are comparable to those expected under climate change during this century.

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  • 32. Tinner, Willy
    et al.
    Bigler, Christian
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Gedye, Sharon
    Gregory-Eaves, Irene
    Jones, Richard T
    Kaltenrieder, Petra
    Krähenbühl, Urs
    Hu, Feng Sheng
    A 700-year paleoecological record of boreal ecosystem responses to climatic variation from Alaska2008In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 89, no 3, p. 729-43Article in journal (Refereed)
    Abstract [en]

    Recent observations and model simulations have highlighted the sensitivity of the forest–tundra ecotone to climatic forcing. In contrast, paleoecological studies have not provided evidence of tree-line fluctuations in response to Holocene climatic changes in Alaska, suggesting that the forest–tundra boundary in certain areas may be relatively stable at multicentennial to millennial time scales. We conducted a multiproxy study of sediment cores from an Alaskan lake near the altitudinal limits of key boreal-forest species. Paleoecological data were compared with independent climatic reconstructions to assess ecosystem responses of the forest–tundra boundary to Little Ice Age (LIA) climatic fluctuations. Pollen, diatom, charcoal, macrofossil, and magnetic analyses provide the first continuous record of vegetation–fire–climate interactions at decadal to centennial time scales during the past 700 years from southern Alaska. Boreal-forest diebacks characterized by declines of Picea mariana, P. glauca, and tree Betula occurred during the LIA (AD 1500–1800), whereas shrubs (Alnus viridis, Betula glandulosa/nana) and herbaceous taxa (Epilobium, Aconitum) expanded. Marked increases in charcoal abundance and changes in magnetic properties suggest increases in fire importance and soil erosion during the same period. In addition, the conspicuous reduction or disappearance of certain aquatic (e.g., Isoetes, Nuphar, Pediastrum) and wetland (Sphagnum) plants and major shifts in diatom assemblages suggest pronounced lake-level fluctuations and rapid ecosystem reorganization in response to LIA climatic deterioration. Our results imply that temperature shifts of 1–28C, when accompanied by major changes in moisture balance, can greatly alter high-altitudinal terrestrial, wetland, and aquatic ecosystems, including conversion between boreal-forest tree line and tundra. The climatic and ecosystem variations in our study area appear to be coherent with changes in solar irradiance, suggesting that changes in solar activity contributed to the environmental instability of the past 700 years.

  • 33. Träger, Sabrina
    et al.
    Öpik, Maarja
    Vasar, Martti
    Wilson, Scott D.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Climate Impacts Research Centre, Umeå University, Abisko, Sweden.
    Belowground plant parts are crucial for comprehensively estimating total plant richness in herbaceous and woody habitats2019In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 100, no 2, article id e02575Article in journal (Refereed)
    Abstract [en]

    Most studies consider aboveground plant species richness as a representative biodiversity measure. This approach inevitably assumes that the partitioning of total plant species richness into above- and belowground components is constant or at least consistent within and across vegetation types. However, with studies considering belowground plant richness still scarce and completely absent along vegetation gradients, this assumption lacks experimental support. Novel DNA sequencing techniques allow economical, high-throughput species identification of belowground environmental samples, enabling the measurement of the contributions of both above- and belowground plant components to total plant richness. We investigated above- and belowground plant species richness in four vegetation types (birch forest, heath, low alpine tundra, high alpine tundra) at the scale of herbaceous plant neighborhoods (dm) using 454 sequencing of the chloroplast trnL (UAA) intron to determine the plant species richness of environmental root samples and combined it with aboveground data from vegetation surveys to obtain total plant species richness. We correlated the measured plant species richness components with each other and with their respective plant biomass components within and across vegetation types. Total plant species richness exceeded aboveground richness twice on average and by as much as three times in low alpine tundra, indicating that a significant fraction of belowground plant richness cannot be recorded aboveground. More importantly, no consistent relationship among richness components (above- and belowground) was found within or across vegetation types, indicating that aboveground richness alone cannot predict total plant richness in contrasting vegetation types. Finally, no consistent relationship between plant richness and the corresponding biomass component was found. Our results clearly show that aboveground plant richness alone is a poor estimator of total plant species richness within and across different vegetation types. Consequently, it is crucial to account for belowground plant richness in future plant ecological studies in order to validate currently accepted plant richness patterns, as well as to measure potential changes in plant community composition in a changing environment.

  • 34.
    Uboni, Alessia
    et al.
    School of Forest Resources and Environmental Science, Michigan Technological University, Houghton, Michigan, USA.
    Vucetich, John A.
    Stahler, Daniel R.
    Smith, Douglas W.
    Interannual variability: a crucial component of space use at the territory level2015In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 96, no 1, p. 62-70Article in journal (Refereed)
    Abstract [en]

    Interannual variability in space use and how that variation is influenced by density-dependent and density-independent factors are important processes in population ecology. Nevertheless, interannual variability has been neglected by the majority of space use studies. We assessed that variation for wolves living in 15 different packs within Yellowstone National Park during a 13-year period (1996–2008). We estimated utilization distributions to quantify the intensity of space use within each pack's territory each year in summer and winter. Then, we used the volume of intersection index (VI) to quantify the extent to which space use varied from year to year. This index accounts for both the area of overlap and differences in the intensity of use throughout a territory and ranges between 0 and 1. The mean VI index was 0.49, and varied considerably, with ~20% of observations (n = 230) being <0.3 or >0.7. In summer, 42% of the variation was attributable to differences between packs. These differences can be attributable to learned behaviors and had never been thought to have such an influence on space use. In winter, 34% of the variation in overlap between years was attributable to interannual differences in precipitation and pack size. This result reveals the strong influence of climate on predator space use and underlies the importance of understanding how climatic factors are going to affect predator populations in the occurrence of climate change. We did not find any significant association between overlap and variables representing density-dependent processes (elk and wolf densities) or intraspecific competition (ratio of wolves to elk). This last result poses a challenge to the classic view of predator–prey systems. On a small spatial scale, predator space use may be driven by factors other than prey distribution.

  • 35.
    Uszko, Wojciech
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Diehl, Sebastian
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Department Biologie II, Ludwig-Maximilians-Universität, München.
    Pitsch, Nadine
    Department Biologie II, Ludwig-Maximilians-Universita¨t Mu¨nchen, Grosshaderner Str. 2, D-82152 Planegg-Martinsried, Germany.
    Lengfellner, Kathrin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Müller, Thomas
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    When is a type III functional response stabilizing?: theory and practice of predicting plankton dynamics under enrichment2015In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 96, no 12, p. 3243-3256Article in journal (Refereed)
    Abstract [en]

    The curvature of generalized Holling type functional response curves is controlled by a shape parameter b yielding hyperbolic type II (b = 1) to increasingly sigmoid type III (b > 1) responses. Empirical estimates of b vary considerably across taxa. Larger consumer-resource body mass ratios have been suggested to generate more pronounced type III responses and therefore to promote dynamic stability. The dependence of consumer-resource stability on b has, however, not been systematically explored, and the accurate empirical determination of b is challenging. Specifically, the shape of the functional response of the pelagic grazer Daphnia feeding on phytoplankton, and its consequences for stability, remain controversial. We derive a novel analytical condition relating b to local stability of consumer-resource interactions and use it to predict stability of empirically parameterized models of Daphnia and phytoplankton under enrichment. Functional response parameters were experimentally derived for two species of Daphnia feeding separately on single cultures of two different phytoplankton species. All experimentally studied Daphnia-algae systems exhibited type III responses. Parameterized type III responses are predicted to stabilize the modeled Daphnia-phytoplankton dynamics in some species pairs but not in others. Remarkably, stability predictions differ depending on whether functional response parameters are derived from clearance vs. ingestion rates. Accurate parameter estimation may therefore require fitting to both rates. In addition, our estimates of b for filter-feeding Daphnia are much smaller than predicted for actively hunting predators at similar consumer-resource body mass ratios. This suggests that the relationship between functional response shape and body mass ratios may vary with predation mode.

  • 36.
    Vasconcelos, Francisco Rivera
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Diehl, Sebastian
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Rodriguez, Patricia
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Austral Centre for Scientific Research (CADIC-CONICET), 9410 Ushuaia, Tierra del Fuego, Argentina.
    Hedström, Per
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Karlsson, Jan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Byström, Pär
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Asymmetrical competition between aquatic primary producers in a warmer and browner world2016In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 97, no 10, p. 2580-2592Article in journal (Refereed)
    Abstract [en]

    In shallow lakes, pelagic and benthic producers engage in spatially asymmetrical resource competition. Pelagic producers intercept the flux of light to the benthic habitat and benthic producers intercept the flux of sediment-derived nutrients to the pelagic habitat. In boreal and subarctic regions, climate change is affecting this interaction both directly through warming and indirectly through increased loading with colored dissolved organic matter (cDOM) from the catchment (brownification). We use a dynamical ecosystem model to explore the consequences of these changing environmental conditions for lake primary production and compare model predictions with the results of an experiment in which we manipulated water temperature and cDOM supply in a 2x2 factorial design. The experiment was performed in field mesocosms large enough to harbor reproducing fish populations and was run over an entire growing season. In agreement with model predictions, benthic algal production and biomass declined and pelagic algal production and biomass increased with browning. Pelagic nutrient concentrations diverged over time between low and high cDOM treatments, suggesting that browning alleviated pelagic algal nutrient limitation by shading benthic competitors and preventing them from intercepting the release of nutrients from the sediment. Warming considerably reduced benthic and pelagic algal production as well as pelagic algalbiomass and total phosphorus. The warming results are only in partial accordance with model expectations, but can be explained by an indirectly inferred, positive response of macrophyte production (which was not included in the model) to warming. Our study suggests that lake ecosystem responses to climate change are mediated by cross-habitat feedbacks between benthic and pelagic producers.

  • 37.
    Wardle, David A.
    et al.
    Swedish Univ Agr Sci, Dept Forest Ecol & Management, SE-90183 Umea, Sweden.
    Jonsson, Micael
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Long-term resilience of above- and belowground ecosystem components among contrasting ecosystems2014In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 95, no 7, p. 1836-1849Article in journal (Refereed)
    Abstract [en]

    While several studies have explored how short-term ecological responses to disturbance vary among ecosystems, experimental studies of how contrasting ecosystems recover from disturbance in the longer term are few. We performed a simple long-term experiment on each of 30 contrasting forested islands in northern Sweden that vary in size; as size decreases, time since fire increases, soil fertility and ecosystem productivity declines, and plant species diversity increases. We predicted that resilience of understory plant community properties would be greatest on the larger, more productive islands, and that this would be paralleled by greater resilience of soil biotic and abiotic properties. For each island, we applied three disturbance treatments of increasing intensity to the forest understory once in 1998, i.e., light trimming, heavy trimming, and burning; a fourth treatment was an undisturbed control. We measured recovery of the understory vascular plant community annually over the following 14 years, and at that time also assessed recovery of mosses and several belowground variables. Consistent with our predictions, vascular plant whole-community variables (total cover, species richness, diversity [Shannon's HI, and community composition) recovered significantly more slowly on the smaller (least fertile) than the larger islands, but this difference was not substantial, and only noticeable in the most severely disturbed treatment. When an index of resilience was used, we were unable to detect effects of island size on the recovery of any property. We found that mosses and one shrub species (Empetrum hermaphroditum) recovered particularly slowly, and the higher abundance of this shrub on small islands was sufficient to explain any slower recovery of whole-ecosystem variables on those islands. Further, several belowground variables had not fully recovered from the most intense disturbance after 14 yr, and counter to our predictions, the degree of their recovery was never influenced by island size. While several studies have shown large variation among plant communities in their short-term response (notably resistance) to environmental perturbations, our results reveal that when perturbations are applied equally to highly contrasting ecosystems, differences in resilience among them in the longer term can be relatively minor, regardless of the severity of disturbance.

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  • 38. Wardle, David A.
    et al.
    Jonsson, Micael
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Kalela-Brundin, Maarit
    Lagerstrom, Anna
    Bardgett, Richard D.
    Yeates, Gregor W.
    Nilsson, Marie-Charlotte
    Drivers of inter-year variability of plant production and decomposers across contrasting island ecosystems2012In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 93, no 3, p. 521-531Article in journal (Refereed)
    Abstract [en]

    Despite the likely importance of inter-year dynamics of plant production and consumer biota for driving community-and ecosystem-level processes, very few studies have explored how and why these dynamics vary across contrasting ecosystems. We utilized a well-characterized system of 30 lake islands in the boreal forest zone of northern Sweden across which soil fertility and productivity vary considerably, with larger islands being more fertile and productive than smaller ones. In this system we assessed the inter-year dynamics of several measures of plant production and the soil microbial community (primary consumers in the decomposer food web) for each of nine years, and soil microfaunal groups (secondary and tertiary consumers) for each of six of those years. We found that, for measures of plant production and each of the three consumer trophic levels, inter-year dynamics were strongly affected by island size. Further, many variables were strongly affected by island size (and thus bottom-up regulation by soil fertility and resources) in some years, but not in other years, most likely due to inter-year variation in climatic conditions. For each of the plant and microbial variables for which we had nine years of data, we also determined the inter-year coefficient of variation (CV), an inverse measure of stability. We found that CVs of some measures of plant productivity were greater on large islands, whereas those of other measures were greater on smaller islands; CVs of microbial variables were unresponsive to island size. We also found that the effects of island size on the temporal dynamics of some variables were related to inter-year variability of macroclimatic variables. As such, our results show that the inter-year dynamics of both plant productivity and decomposer biota across each of three trophic levels, as well as the inter-year stability of plant productivity, differ greatly across contrasting ecosystems, with potentially important but largely overlooked implications for community and ecosystem processes.

  • 39. Wellenreuther, Maren
    et al.
    Larson, Keith W.
    Evolutionary Ecology Unit, Department of Biology, Ecology Building, Lund University, SE-223 62 Lund, Sweden.
    Svensson, Erik I.
    Climatic niche divergence or conservatism?: Environmental niches and range limits in ecologically similar damselflies2012In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 93, no 6, p. 1353-1366Article in journal (Refereed)
    Abstract [en]

    The factors that determine species' range limits are of central interest to biologists. One particularly interesting group comprises odonates (dragonflies and damselflies), which show large differences in secondary sexual traits and respond quickly to climatic factors, but often have minor interspecific niche differences, challenging models of niche-based species coexistence. We quantified the environmental niches at two geographic scales to understand the ecological causes of northern range limits and the coexistence of two congeneric damselflies (Calopteryx splendens and C. virgo). Using environmental niche modeling, we quantified niche divergence first across the whole geographic range in Fennoscandia, and second only in the sympatric part of this range. We found evidence for interspecific divergence along the environmental axes of temperature and precipitation across the northern range in Fennoscandia, suggesting that adaptation to colder and wetter climate might have allowed C. virgo to expand farther north than C. splendens. However, in the sympatric zone in southern Fennoscandia we found only negligible and nonsignificant niche differences. Minor niche differences in sympatry lead to frequent encounters and intense interspecific sexual interactions at the local scale of populations. Nevertheless, niche differences across Fennoscandia suggest that species differences in physiological tolerances limit range expansions northward, and that current and future climate could have large effects on the distributional ranges of these and ecologically similar insects.

  • 40.
    Wiedermann, Magdalena M.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Nordin, Annika
    Gunnarsson, Urban
    Nilsson, Mats B.
    Ericson, Lars
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Global change shifts vegetation and plant-parasite interactions in a boreal mire2007In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 88, no 2, p. 454-464Article in journal (Refereed)
    Abstract [en]

    The aim of this study was to detect vegetation change and to examine trophic interactions in a Sphagnum-dominated mire in response to raised temperature and nitrogen (N) addition. A long-term global-change experiment was established in 1995, with monthly additions of N (30 kg·ha-1·yr-1) and sulfur (20 kg·ha-1·yr-1) during the vegetation period. Mean air temperature was raised by 3.6°C with warming chambers. Vegetation responses were negligible for all treatments for the first four years, and no sulfur effect was seen during the course of the experiment. However, after eight years of continuous treatments, the closed Sphagnumcarpet was drastically reduced from 100 in 1995 down to 41, averaged over all N-treated plots. Over the same period, total vascular plant cover (of the graminoid Eriophorum vaginatumand the two dwarf-shrubs Andromeda polifoliaand Vaccinium oxycoccos) increased from 24 to an average of 70 in the N plots. Nitrogen addition caused leaf N concentrations to rise in the two dwarf-shrubs, while for E. vaginatum, leaf N remained unchanged, indicating that the graminoid to a larger extent than the dwarf-shrubs allocated supplemented N to growth. Concurrent with foliar N accumulation of the two dwarf-shrubs, we observed increased disease incidences caused by parasitic fungi, with three species out of 16 showing a significant increase. Warming caused a significant decrease in occurrence of three parasitic fungal species. In general, decreased disease incidences were found in temperature treatments for A. polifoliaand in plots without N addition for V. oxycoccos. The study demonstrates that both bryophytes and vascular plants at boreal mires, only receiving background levels of nitrogen of about 2 kg·ha-1·yr-1, exhibit a time lag of more than five years in response to nitrogen and temperature rise, emphasizing the need for long-term experiments. Moreover, it shows that trophic interactions are likely to differ markedly in response to climate change and increased N deposition, and that these interactions might play an important role in controlling the change in mire vegetation composition, with implications for both carbon sequestration and methane emission.

  • 41. Wollrab, Sabine
    et al.
    de Roos, Andre M.
    Diehl, Sebastian
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Ontogenetic diet shifts promote predator-mediated coexistence2013In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 94, no 12, p. 2886-2897Article in journal (Refereed)
    Abstract [en]

    It is widely believed that predation moderates interspecific competition and promotes prey diversity. Still, in models of two prey sharing a resource and a predator, predator-mediated coexistence occurs only over narrow ranges of resource productivity. These models have so far ignored the widespread feature of ontogenetic diet shifts in predators. Here, we theoretically explore the consequences of a diet shift from juvenile to adult predator stages for coexistence of two competing prey. We find that only very minor deviations from perfectly identical diets in juveniles and adults destroy the traditional mechanism of predator-mediated coexistence, which requires an intrinsic trade-off between prey defendedness and competitive ability. Instead, predator population structure can create an emergent competition-predation trade-off between prey, where a bottleneck in one predator stage enhances predation on the superior competitor and relaxes predation on the inferior competitor, irrespective of the latter's intrinsic defendedness. Pronounced diet shifts therefore greatly enlarge the range of prey coexistence along a resource gradient. With diet shifts, however, coexistence usually occurs as one of two alternative states and, once lost, may not be easily restored.

  • 42.
    Åström, Marcus
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Dynesius, Mats
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Hylander, Kristoffer
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Slope aspect modifies community responses to clear-cutting in boreal forests2007In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 88, no 3, p. 749-758Article in journal (Refereed)
    Abstract [en]

    Slope aspect modifies microclimate and influences ecological processes and spatial distribution of species across forest landscapes, but the impact of slope aspect on community responses to disturbance is poorly understood. Such insight is necessary to understand landscape community dynamics and resilience. We compared bryophyte (liverworts and mosses) communities in matched 0.02-ha plots of four boreal stand types in central Sweden: recently clear-felled and mature stands dominated by Norway spruce in south-facing and north-facing slopes. Differences between forests and clear-cuts were interpreted as effects of clear-cutting, and differences between south- and north-facing slopes as effects of aspect. In response to clear-cutting, bryophyte cover and composition changed more in south-facing slopes. Only one out of ten significantly declining species in south-facing slopes also declined significantly in north-facing slopes. North-facing slopes lost fewer bryophyte species, and among those, fewer forest species and fewer species associated with wood and bark. In north-facing slopes, the average proportions of mosses and liverworts shared between the forest and the clear-cut plot were 88% and 74%, respectively. Corresponding numbers for south-facing slopes were 79% and 33%. In addition, more bryophyte species were added in north- than south-facing slopes after clear-cutting, somewhat reducing the difference in compositional change between aspects. South- and north-facing mature forests differed in species composition, mostly due to higher richness of mosses in south-facing slopes. The smaller changes in bryophyte communities on north-facing slopes in response to clear-cutting have implications for ecosystem dynamics and management as high local survival may enhance landscape-level resilience.

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    Åström et al_Ecology2007
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