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  • 1.
    Ahlbeck, Ida
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Systemekologiska institutionen.
    Hansson, Sture
    Stockholms universitet, Naturvetenskapliga fakulteten, Systemekologiska institutionen.
    Hjerne, Olle
    Stockholms universitet, Naturvetenskapliga fakulteten, Systemekologiska institutionen.
    Evaluating fish diet analysis methods by individual-based modelling2012Ingår i: Canadian Journal of Fisheries and Aquatic Sciences, ISSN 0706-652X, E-ISSN 1205-7533, Vol. 69, nr 7, s. 1184-1201Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Knowledge of diet compositions is important in ecological research. There are many methods available and numerous aspects of diet composition. Here we used modelling to evaluate how well different diet analysis methods describe the true diet of fish, expressed in mass percentages. The methods studied were both basic methods (frequency of occurrence, dominance, numeric, mass, points) and composite indices (Index of Relative Importance, Comparative Feeding Index). Analyses were based on both averaged stomach content of individual fish and on pooled content from several fish. Prey preference, prey size, and evacuation rate influenced the performance of the diet analysis methods. The basic methods performed better than composite indices. Mass and points methods produced diet compositions most similar to the true diet and were also most robust, indicating that these methods should be used to describe energetic-nutritional sources of fish.

  • 2.
    Ahlbeck, Ida
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Systemekologiska institutionen.
    Hansson, Sture
    Stockholms universitet, Naturvetenskapliga fakulteten, Systemekologiska institutionen.
    Hjerne, Olle
    Stockholms universitet, Naturvetenskapliga fakulteten, Systemekologiska institutionen.
    Evaluation of diet analysis methods by individual based modellingIngår i: Canadian Journal of Fisheries and Aquatic Sciences, ISSN 0706-652X, E-ISSN 1205-7533Artikel i tidskrift (Refereegranskat)
  • 3.
    Angeler, David G.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik. Swedish University of Agricultural Sciences, Sweden.
    Allen, Craig R.
    Garmestani, Ahjond S.
    Gunderson, Lance H.
    Hjerne, Olle
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Winder, Monika
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Quantifying the Adaptive Cycle2015Ingår i: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 10, nr 12, artikel-id e0146053Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The adaptive cycle was proposed as a conceptual model to portray patterns of change in complex systems. Despite the model having potential for elucidating change across systems, it has been used mainly as a metaphor, describing system dynamics qualitatively. We use a quantitative approach for testing premises (reorganisation, conservatism, adaptation) in the adaptive cycle, using Baltic Sea phytoplankton communities as an example of such complex system dynamics. Phytoplankton organizes in recurring spring and summer blooms, a well-established paradigm in planktology and succession theory, with characteristic temporal trajectories during blooms that may be consistent with adaptive cycle phases. We used long-term (1994-2011) data and multivariate analysis of community structure to assess key components of the adaptive cycle. Specifically, we tested predictions about: reorganisation: spring and summer blooms comprise distinct community states; conservatism: community trajectories during individual adaptive cycles are conservative; and adaptation: phytoplankton species during blooms change in the long term. All predictions were supported by our analyses. Results suggest that traditional ecological paradigms such as phytoplankton successional models have potential for moving the adaptive cycle from a metaphor to a framework that can improve our understanding how complex systems organize and reorganize following collapse. Quantifying reorganization, conservatism and adaptation provides opportunities to cope with the intricacies and uncertainties associated with fast ecological change, driven by shifting system controls. Ultimately, combining traditional ecological paradigms with heuristics of complex system dynamics using quantitative approaches may help refine ecological theory and improve our understanding of the resilience of ecosystems.

  • 4.
    Downing, Andrea S.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik. Stockholms universitet, Naturvetenskapliga fakulteten, Stockholm Resilience Centre.
    Hajdu, Susanna
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Hjerne, Olle
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Otto, Saskia A.
    Stockholms universitet, Naturvetenskapliga fakulteten, Stockholm Resilience Centre.
    Blenckner, Thorsten
    Stockholms universitet, Naturvetenskapliga fakulteten, Stockholm Resilience Centre.
    Larsson, Ulf
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Winder, Monika
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Zooming in on size distribution patterns underlying species coexistence in Baltic Sea phytoplankton2014Ingår i: Ecology Letters, ISSN 1461-023X, E-ISSN 1461-0248, Vol. 17, nr 10, s. 1219-1227Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Scale is a key to determining which processes drive community structure. We analyse size distributions of phytoplankton to determine time scales at which we can observe either fixed environmental characteristics underlying communities structure or competition-driven size distributions. Using multiple statistical tests, we characterise size distributions of phytoplankton from 20-year time series in two sites of the Baltic Sea. At large temporal scales (5-20 years), size distributions are unimodal, indicating that fundamental barriers to existence are here subtler than in other systems. Frequency distributions of the average size of the species weighted by biovolume are multimodal over large time scales, although this is the product of often unimodal short-term (<1 year) patterns. Our study represents a much-needed structured, high-resolution analysis of phytoplankton size distributions, revealing that short-term analyses are necessary to determine if, and how, competition shapes them. Our results provide a stepping-stone on which to further investigate the intricacies of competition and coexistence.

  • 5.
    Hansson, Sture
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Systemekologiska institutionen. marin ekologi.
    Hjerne, Olle
    Stockholms universitet, Naturvetenskapliga fakulteten, Systemekologiska institutionen. marin ekologi.
    Harvey, C
    Kitchell, JF
    Cox, SP
    Essington, TE
    Managing Baltic Sea fisheries under contrasting production and predation regimes: ecosystem model analyses2007Ingår i: Ambio, Vol. 36, nr 2-3, s. 259-265Artikel i tidskrift (Refereegranskat)
  • 6.
    Hjerne, Olle
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Hajdu, Susanna
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Larsson, Ulf
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Downing, Andrea S.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik. Stockholms universitet, Naturvetenskapliga fakulteten, Stockholm Resilience Centre.
    Winder, Monika
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Climate Driven Changes in Timing, Composition and Magnitude of the Baltic Sea Phytoplankton Spring Bloom2019Ingår i: Frontiers in Marine Science, E-ISSN 2296-7745, Vol. 6, artikel-id 482Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Spring phytoplankton blooms contribute a substantial part to annual production, support pelagic and benthic secondary production and influence biogeochemical cycles in many temperate aquatic systems. Understanding environmental effects on spring bloom dynamics is important for predicting future climate responses and for managing aquatic systems. We analyzed long-term phytoplankton data from one coastal and one offshore station in the Baltic Sea to uncover trends in timing, composition and size of the spring bloom and its correlations to environmental variables. There was a general trend of earlier phytoplankton blooms by 1-2 weeks over the last 20 years, associated with more sunshine and less windy conditions. High water temperatures were associated with earlier blooms of diatoms and dinoflagellates that dominate the spring bloom, and decreased diatom bloom magnitude. Overall bloom timing, however, was buffered by a temperature and ice related shift in composition from early blooming diatoms to later blooming dinoflagellates and the autotrophic ciliate Mesodinium rubrum. Such counteracting responses to climate change highlight the importance of both general and taxon-specific investigations. We hypothesize that the predicted earlier blooms of diatoms and dinoflagellates as a response to the expected temperature increase in the Baltic Sea might also be counteracted by more clouds and stronger winds. A shift from early blooming and fast sedimenting diatoms to later blooming groups of dinoflagellates and M. rubrum at higher temperatures during the spring period is expected to increase energy transfers to pelagic secondary production and decrease spring bloom inputs to the benthic system, resulting in lower benthic production and reduced oxygen consumption.

  • 7. Lundström, Karl
    et al.
    Hjerne, Olle
    Stockholms universitet, Naturvetenskapliga fakulteten, Systemekologiska institutionen.
    Lunneryd, Sven-Gunnar
    Karlsson, Olle
    Understanding the diet composition of marine mammals: grey seals (Halichoerus grypus) in the Baltic Sea2010Ingår i: ICES Journal of Marine Science, ISSN 1054-3139, E-ISSN 1095-9289, Vol. 67, nr 6, s. 1230-1239Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Dietary studies are important in understanding the ecological role of marine mammals and in formulating appropriate management plans in terms of their interactions with fisheries. The validity of such studies has, however, often been compromised by unrepresentative sampling procedures, resulting in false weight being given to external factors seeming to influence diet composition. The bias caused by non-random sampling was examined, using canonical correspondence analysis to assess how the prey species composition in digestive tract samples of Baltic grey seals (Halichoerus grypus) was related to spatial, temporal, and demographic factors and to whether the samples were collected in association with fishing gear or not (“sampling condition”). Geographic region explained the largest fraction of the observed variation, followed by sampling condition, age group, and year. Season and gender were not statistically significant. Segregation of the two age categories “pups” and “juveniles–adults”, and the two geographic categories “Baltic proper” and “Gulf of Bothnia” are proposed to estimate the diet and fish consumption of the Baltic grey seal population as a whole. Atlantic herring was the most commonly recovered prey item in all areas and age groups, followed by European sprat in the south, and common whitefish in the north. Pups had eaten relatively more small non-commercial species than older seals.

  • 8.
    Niiranen, Susa
    et al.
    Stockholms universitet, Stockholm Resilience Centre, Baltic Nest Institute.
    Blenckner, Thorsten
    Stockholms universitet, Stockholm Resilience Centre, Baltic Nest Institute.
    Hjerne, Olle
    Stockholms universitet, Naturvetenskapliga fakulteten, Systemekologiska institutionen.
    Tomczak, Maciej T.
    Stockholms universitet, Stockholm Resilience Centre, Baltic Nest Institute.
    Uncertainties in a Baltic Sea Food-Web Model Reveal Challenges for Future Projections2012Ingår i: Ambio, ISSN 0044-7447, E-ISSN 1654-7209, Vol. 41, nr 6, s. 613-625Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Models that can project ecosystem dynamics under changing environmental conditions are in high demand. The application of such models, however, requires model validation together with analyses of model uncertainties, which are both often overlooked. We carried out a simplified model uncertainty and sensitivity analysis on an Ecopath with Ecosim food-web model of the Baltic Proper (BaltProWeb) and found the model sensitive to both variations in the input data of pre-identified key groups and environmental forcing. Model uncertainties grew particularly high in future climate change scenarios. For example, cod fishery recommendations that resulted in viable stocks in the original model failed after data uncertainties were introduced. In addition, addressing the trophic control dynamics produced by the food-web model proved as a useful tool for both model validation, and for studying the food-web function. These results indicate that presenting model uncertainties is necessary to alleviate ecological surprises in marine ecosystem management.

  • 9.
    Niiranen, Susa
    et al.
    Stockholms universitet, Stockholm Resilience Centre.
    Blenckner, Thorsten
    Stockholms universitet, Stockholm Resilience Centre.
    Yletyinen, Johanna
    Stockholms universitet, Stockholm Resilience Centre.
    Otto, Saskia
    Stockholms universitet, Stockholm Resilience Centre.
    Meier, H. E. Markus
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Hjerne, Olle
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Tomczak, Maciej T
    Stockholms universitet, Stockholm Resilience Centre, Baltic Nest Institute.
    The potential risk of regime shifts and changes in ecosystem dynamics in the future Baltic SeaArtikel i tidskrift (Refereegranskat)
  • 10.
    Niiranen, Susa
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Stockholm Resilience Centre. Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Yletyinen, Johanna
    Stockholms universitet, Naturvetenskapliga fakulteten, Stockholm Resilience Centre. University of Olso, Norway.
    Tomczak, Maciej T.
    Stockholms universitet, Naturvetenskapliga fakulteten, Stockholms universitets Östersjöcentrum, Baltic Nest Institute.
    Blenckner, Thorsten
    Stockholms universitet, Naturvetenskapliga fakulteten, Stockholm Resilience Centre.
    Hjerne, Olle
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    MacKenzie, Brian R.
    Müller-Karulis, Bärbel
    Stockholms universitet, Naturvetenskapliga fakulteten, Stockholms universitets Östersjöcentrum, Baltic Nest Institute.
    Neumann, Thomas
    Meier, H. E. Markus
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU). Swedish Meteorological and Hydrological Institute, Sweden.
    Combined effects of global climate change and regional ecosystem drivers on an exploited marine food web2013Ingår i: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 19, nr 11, s. 3327-3342Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Changes in climate, in combination with intensive exploitation of marine resources, have caused large-scale reorganizations in many of the world's marine ecosystems during the past decades. The Baltic Sea in Northern Europe is one of the systems most affected. In addition to being exposed to persistent eutrophication, intensive fishing, and one of the world's fastest rates of warming in the last two decades of the 20th century, accelerated climate change including atmospheric warming and changes in precipitation is projected for this region during the 21st century. Here, we used a new multi-model approach to project how the interaction of climate, nutrient loads and cod fishing may affect the future of the open Central Baltic Sea food web. Regionally downscaled global climate scenarios were, in combination with three nutrient load scenarios, used to drive an ensemble of three regional biogeochemical models (BGMs). An Ecopath with Ecosim food web model was then forced with the BGM results from different nutrient-climate scenarios in combination with two different cod fishing scenarios. The results showed that regional management is likely to play a major role in determining the future of the Baltic Sea ecosystem. By the end of the 21st century, for example, the combination of intensive cod fishing and high nutrient loads projected a strongly eutrophicated and sprat-dominated ecosystem, while low cod fishing in combination with low nutrient loads resulted in a cod-dominated ecosystem with eutrophication levels close to present. Also, non-linearities were observed in the sensitivity of different trophic groups to nutrient loads or fishing depending on the combination of the two. Finally, many climate variables and species biomasses were projected to levels unseen in the past. Hence, the risk for ecological surprises needs to be addressed, particularly when the results are discussed in the ecosystem-based management context.

  • 11.
    Tomczak, Macief
    et al.
    Stockholms universitet, Stockholm Resilience Centre, Baltic Nest Institute.
    Niiranen, Susa
    Stockholms universitet, Stockholm Resilience Centre, Baltic Nest Institute. Stockholms universitet, Naturvetenskapliga fakulteten, Systemekologiska institutionen.
    Hjerne, Olle
    Stockholms universitet, Naturvetenskapliga fakulteten, Systemekologiska institutionen.
    Blenckner, Thorsten
    Stockholms universitet, Stockholm Resilience Centre, Baltic Nest Institute.
    Ecosystem flow dynamics in the Baltic Proper-Using a multi-trophic dataset as a basis for food-web modelling2012Ingår i: Ecological Modelling, ISSN 0304-3800, E-ISSN 1872-7026, Vol. 230, s. 123-147Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Baltic Proper is a semi-enclosed, highly productive basin of the Baltic Sea with a low biodiversity, where only a few key species drive the system's dynamics. Recently, an ecosystem regime shift was described having pronounced changes at all trophic levels, driven by changes in fishery and climate and leading to a food-web reorganisation. An Ecopath with Ecosim Baltic Proper food-web model (BaltProWeb) was developed to simulate and better understand trophic interactions and their flows. The model contains 22 functional groups that represent the main food-web components. BaltProWeb was calibrated to long-term monitoring data (1974-2006), covering multiple trophic levels and is forced by fisheries and environmental drivers. Our model enables the quantification of the flows through the food-web from primary producers to top predators including fisheries over time. The model is able to explain 51% of the variation in biomass of multiple trophic levels and to simulate the regime shift from a cod dominated to a sprat dominated system. Results show a change from benthic to more pelagic trophic flows. Before the reorganisation macrozoobenthos was identified as an important functional group transferring energy directly from lower trophic levels to top predators. After the regime shift, the pelagic trophic flows dominated. Uncertainties and limitations of the modelling approach and results in relation to ecosystem-based management are discussed.

  • 12.
    Österblom, Henrik
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för systemekologi. Stockholms universitet, Stockholm Resilience Centre.
    Hansson, Sture
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för systemekologi.
    Larsson, Ulf
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för systemekologi.
    Hjerne, Olle
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för systemekologi.
    Wulff, Fredrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för systemekologi. Stockholms universitet, Stockholm Resilience Centre.
    Elmgren, Ragnar
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för systemekologi.
    Folke, Carl
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för systemekologi. Stockholms universitet, Stockholm Resilience Centre.
    Human-induced trophic cascades and ecological regime shifts in the Baltic Sea2007Ingår i: Ecosystems (New York. Print), ISSN 1432-9840, E-ISSN 1435-0629, Vol. 10, nr 6, s. 877-889Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The ecosystems of coastal and enclosed seas are under increasing anthropogenic pressure worldwide, with Chesapeake Bay, the Gulf of Mexico and the Black and Baltic Seas as well known examples. We use an ecosystem model (Ecopath with Ecosim, EwE) to show that reduced top-down control (seal predation) and increased bottom-up forcing (eutrophication) can largely explain the historical dynamics of the main fish stocks (cod, herring and sprat) in the Baltic Sea between 1900 and 1980. Based on these results and the historical fish stock development we identify two major ecological transitions. A shift from seal to cod domination was caused by a virtual elimination of marine mammals followed by a shift from an oligotrophic to a eutrophic state. A third shift from cod to clupeid domination in the late 1980s has previously been explained by overfishing of cod and climatic changes. We propose that the shift from an oligotrophic to a eutrophic state represents a true regime shift with a stabilizing mechanism for a hysteresis phenomenon. There are also mechanisms that could stabilize the shift from a cod to clupeid dominated ecosystem, but there are no indications that the ecosystem has been pushed that far yet. We argue that the shifts in the Baltic Sea are a consequence of human impacts, although variations in climate may have influenced their timing, magnitude and persistence.

1 - 12 av 12
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