| 1. |
- Persson, Frank, 1970, et al.
(author)
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Ecological role of a seaweed secondary metabolite for a colonizing bacterial community
- 2011
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In: Biofouling. - : Informa UK Limited. - 0892-7014 .- 1029-2454. ; 27:6, s. 579-588
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Journal article (peer-reviewed)abstract
- Bacteria associated with seaweeds can both harm and benefit their hosts. Many seaweed species are known to produce compounds that inhibit growth of bacterial isolates, but the ecological role of seaweed metabolites for the associated bacterial community structure is not well understood. In this study the response of a colonizing bacterial community to the secondary metabolite (1,1,3,3-tetrabromo-2-heptanone) from the red alga Bonnemaisonia hamifera was investigated by using field panels coated with the metabolite at a range of concentrations covering those measured at the algal surface. The seaweed metabolite has previously been shown to have antibacterial effects. The metabolite significantly affected the natural fouling community by (i) altering the composition, (ii) altering the diversity by increasing the evenness and (iii) decreasing the density, as measured by terminal restriction fragment length polymorphism in conjunction with clone libraries of the 16S rRNA genes and by bacterial enumeration. No single major bacterial taxon (phylum, class) was particularly affected by the metabolite. Instead changes in community composition were observed at a more detailed phylogenetic level. This indicates a broad specificity of the seaweed metabolite against bacterial colonization, which is supported by the observation that the bacterial density was significantly affected at a lower concentration (0.02 μg cm -2) than the composition (1-2.5 μg cm -2) and the evenness (5 μg cm -2) of the bacterial communities. Altogether, the results emphasize the role of secondary metabolites for control of the density and structure of seaweed-associated bacterial communities.
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| 2. |
- Lindegarth, Mats, 1965, et al.
(author)
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Testing the Potential for Predictive Modeling and Mapping and Extending Its Use as a Tool for Evaluating Management Scenarios and Economic Valuation in the Baltic Sea (PREHAB)
- 2014
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In: Ambio. - : Springer Science and Business Media LLC. - 0044-7447 .- 1654-7209. ; 43:1, s. 82-93
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Journal article (peer-reviewed)abstract
- We evaluated performance of species distribution models for predictive mapping, and how models can be used to integrate human pressures into ecological and economic assessments. A selection of 77 biological variables (species, groups of species, and measures of biodiversity) across the Baltic Sea were modeled. Differences among methods, areas, predictor, and response variables were evaluated. Several methods successfully predicted abundance and occurrence of vegetation, invertebrates, fish, and functional aspects of biodiversity. Depth and substrate were among the most important predictors. Models incorporating water clarity were used to predict increasing cover of the brown alga bladderwrack Fucus vesiculosus and increasing reproduction area of perch Perca fluviatilis, but decreasing reproduction areas for pikeperch Sander lucioperca following successful implementation of the Baltic Sea Action Plan. Despite variability in estimated non-market benefits among countries, such changes were highly valued by citizens in the three Baltic countries investigated. We conclude that predictive models are powerful and useful tools for science-based management of the Baltic Sea.
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| 3. |
- Pavia, Henrik, 1964, et al.
(author)
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Chemical defences against herbivores
- 2012
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In: Chemical ecology in aquatic systems. - New York, US : Oxford University Press. - 9780199583096 ; , s. 210-235
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Book chapter (peer-reviewed)abstract
- In recent years it has become increasingly clear that chemical interactions play a fundamental role in aquatic habitats and have far-reaching evolutionary and ecological consequences. A plethora of studies have shown that aquatic organisms from most taxa and functional groups respond to minute concentrations of chemical substances released by other organisms. However, our knowledge of this 'chemical network' is still negligible. Chemical interactions can be divided into two larger sub-areas based on the function of the chemical substance. First, there are interactions where chemical substances are toxic to other organisms and are used as a defense against consumers (including both herbivores and predators) or a weapon against competitors (allelopathy). Second, chemical substances mey be used as a source for information of the environment; for example: how can I find the optimal habitat, the best food, the nicest partner, and avoid being eaten? Aquatic organisms are able to detect and respond to extremely low concentrations of chemical cues to answer all these questions. The book aims at connecting these intriguing chemical interactions with traditional knowledge of organism interactions. Chemical ecology in aquatic systems covers a wide range of studies, both plant and animal, from different geographic regions and habitats-pelagic as well as benthic. Most of the chemical interactions are similar in freshwater and marine habitats and this book therefor strives at integrating work on both systems. This accessible, research-level text is aimed at graduate students and professional researchers in the fields of limnology, marine ecology, evolutionary biology, behavioral ecology, and chemical ecology.
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| 4. |
- Svensson, J. Robin, 1979, et al.
(author)
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Disturbance-diversity models: what do they really predict and how are they tested?
- 2012
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In: Proceedings of the Royal Society of London. Biological Sciences. - : The Royal Society. - 0962-8452 .- 1471-2954. ; 279:1736, s. 2163-2170
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Journal article (peer-reviewed)abstract
- The intermediate disturbance hypothesis (IDH) and the dynamic equilibrium model (DEM) are influential theories in ecology. The IDH predicts large species numbers at intermediate levels of disturbance and the DEM predicts that the effect of disturbance depends on the level of productivity. However, various indices of diversity are considered more commonly than the predicted number of species in tests of the hypotheses. This issue reaches beyond the scientific community as the predictions of the IDH and the DEM are used in the management of national parks and reserves. In order to compare responses with disturbance among measures of biodiversity, we used two different approaches of mathematical modelling and conducted an extensive meta-analysis. Two-thirds of the surveyed studies present different results for different diversity measures. Accordingly, the meta-analysis showed a narrow range of negative quadratic regression components for richness, but not evenness. Also, the two models support the IDH and the DEM, respectively, when biodiversity is measured as species richness, but predict evenness to increase with increasing disturbance, for all levels of productivity. Consequently, studies that use compound indices of diversity should present logical arguments, a priori, to why a specific index of diversity should peak in response to disturbance.
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| 5. |
- Svensson, J. Robin, 1979
(author)
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Ecological disturbances: the good, the bad and the ugly
- 2010
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Doctoral thesis (other academic/artistic)abstract
- Abstract. This thesis focuses on the definitions, characterizations and quantifications of ecological disturbances, as well as hypotheses on their impacts on biological communities. The most prominent model on effects of disturbance on diversity is the Intermediate Disturbance Hypothesis (IDH), which is utilized in management of national reserves, has received over 3300 citations and has been corroborated by a multitude of studies from terrestrial and aquatic systems. According to the predictions of the IDH, diversity is high at intermediate levels of disturbance due to coexistence of competitors and colonizers. At low levels of disturbance diversity will be low due to competitive exclusion and few species can persist at high levels of disturbance. In an extension of the IDH, the Dynamic Equilibrium Model (DEM) predicts that the effects of disturbance depend on the productivity of communities, because at high growth rates a stronger disturbance is required to counteract increased rates of competitive exclusion. The IDH and the DEM were tested in a field experiment on effects of physical disturbance (scraping) and productivity (nutrient availability) on hard-substratum assemblages in paper I, where the patterns predicted by the IDH, but not the DEM, were observed. This outcome shows the importance of the nature of productivity alterations, as the productivity treatment had a general positive effect on growth rates but only marginal effects on the dominant species, thereby leaving rates of competitive exclusion unaffected. In paper II I tested another extension of the IDH, which predicts that smaller, more frequent disturbances will have different effects on diversity compared to larger, less frequent disturbances. In this experiment I used two different regimes of disturbance, small and frequent vs. large and infrequent disturbances, while the overall rate (the product of area and frequency) was kept equal for both regimes. At the site where the IDH was supported, the regime with a large proportion of the area disturbed infrequently showed higher richness, due to a stronger decrease of dominants, compared to the regime with a small proportion disturbed frequently. In addition to these significant differences in diversity effects between different disturbance regimes, it may also matter what agent of disturbance that is causing the damage. In paper III I contrasted the effects of a physical disturbance (wave-action) to that of a biological disturbance (grazing), as well as their respective interactions with productivity in a multifactorial design tested on natural epilithic assemblages. The composition of assemblages and the total species richness was significantly affected by physical disturbance and interactively by biological disturbance and productivity. The algal richness was significantly affected by productivity and biological disturbance, whereas the invertebrate richness was affected by physical disturbance. The results show, for the first time, that biological disturbance and physical disturbance interact differently with productivity due to differences in the distribution and selectivity among disturbances. In paper IV I investigate how the choice of diversity measure may impact the outcomes of tests of the IDH, which, surprisingly, has not previously been discussed. This was done by an extensive literature review and meta-analysis on published papers as well as by two different approaches to mathematical modelling. Both models support the IDH when biodiversity is measured as species richness, but not evenness. The meta-analysis showed that two-thirds of the published studies in the survey present different results for different diversity measures. Hence, the choice of diversity measure is vital for the outcome of tests of the IDH and related models.
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| 6. |
- Svensson, J. Robin, 1979, et al.
(author)
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Excessive spatial resolution decreases performance of quantitative models, contrary to expectations from error analyses
- 2013
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In: Marine Ecology Progress Series. - : Inter-Research Science Center. - 0171-8630 .- 1616-1599. ; 485, s. 57-73
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Journal article (peer-reviewed)abstract
- Increased focus on predictive aspects of ecology has recently been urged by scientists and policy makers to provide solutions to pressing societal needs. Current challenges include the large knowledge gap on the spatial distribution of marine biodiversity, and its associated goods and services, and the dependence of model performance on spatial resolution. We evaluated the importance of resolution on the predictive power and precision of empirical models of distributions of marine sessile invertebrates and macroalgae along the Swedish west coast. This was done by simulating the limits to prediction, based on 2 independent simulated proportions of biological variables, and comparing these limits to observed models at different resolutions. Simulations showed the highest achievable predictive power (r(2)) and precision (RMSE) of models at fine resolutions (similar to 1 m). In contrast to the simulations, the performance of quantitative models was better at relatively coarse resolutions (similar to 100 m). Increased model performance at coarse resolutions could not be explained by differences in sampling or spatial variability. Instead, the improvement is likely caused by the mechanistic coupling (direct or indirect) between predictor variables, depth and hard substratum cover and patterns at coarser scales, whereas complex processes, e. g. biological interactions, shape patterns at finer scales. This match between resolution and the scale at which environmental variables operate may differ among systems, which could explain the discrepancy in outcomes between our study and previous studies. Furthermore, we provide an approach for error analysis that identifies contributions of different model components to the total uncertainty, thus facilitating model optimization.
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| 7. |
- Svensson, J. Robin, 1979, et al.
(author)
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Novel chemical weapon of an exotic macroalga inhibits recruitment of native competitors in the invaded range
- 2013
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In: Journal of Ecology. - : Wiley. - 0022-0477 .- 1365-2745. ; 101:1, s. 140-148
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Journal article (peer-reviewed)abstract
- 1. Allelopathy is an important non-resource interaction in terrestrial plant communities that may affect invasions by non-indigenous plants. The ‘novel weapons hypothesis’ (NWH) predicts that non-indigenous plants will become invasive if they have allelopathic compounds that assem- blages in the new range are not adapted to. Recently, the non-indigenous, chemically rich macroalga Bonnemaisonia hamifera (Hariot) has become one of the most abundant filamentous red algae in Scandinavian waters. 2. We used B. hamifera to specifically test the aspect of the NWH that concerns invasion success based on novel allelochemicals in the invaded range. Allelopathic interactions were tested through effects on the growth rate of adult native macroalgae in co-cultures with B. hamifera and through the settlement success of native macroalgal propagules and microalgae on surfaces coated with 1,1,3,3-tetrabromo-2-heptanone. We also investigated whether 1,1,3,3-tetrabromo-2-heptanone can be transferred from B. hamifera to its native host algae, as a means of pre-emptive competition. 3. The settlement of native macroalgal propagules and microalgae was strongly inhibited on surfaces coated with 1,1,3,3-tetrabromo-2-heptanone at ecologically relevant concentrations, but there were no effects of adult B. hamifera on growth rates of adults of the six native naturally co-occurring spe- cies. The compound was shown to be transferred from B. hamifera to the surface of its native host algae at inhibitory concentrations in both laboratory and field experiments. 4. By inhibiting the settlement of propagules on its thallus and on surrounding surfaces, B. hamifera achieves a competitive advantage over native macroalgae, a finding that parallels previous reports on soil- and litter-mediated allelopathic interactions among vascular plants. Because competition for available substrata in marine benthic systems is intense, the ability to reserve space may be vital for B. hamifera’s successful invasion. This is the first example of an allelopathic compound that can be transferred by direct contact from an exotic to a native species, with an active and unaltered func- tion. 5. Synthesis. Our results clearly show that the main secondary metabolite of the invasive red alga B. hamifera has strong allelopathic effects towards native competitors, suggesting that its novel chemical weapon is important for the highly successful invasion of new ranges.
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| 8. |
- Svensson, J. Robin, 1979, et al.
(author)
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Physical and biological disturbance interacts differently with productivity: divergence in effects on floral and faunal richness
- 2010
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In: Ecology. - 0012-9658. ; 91:10, s. 3069-3080
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Journal article (peer-reviewed)abstract
- Physical and biological disturbance are ecological processes affecting patterns in biodiversity at a range of scales in a variety of terrestrial and aquatic systems. Theoretical and empirical evidence suggest that effects of disturbance on diversity differ qualitatively and quantitatively depending on levels of productivity (e.g. the dynamic equilibrium model). In this study we contrasted the interactive effects between physical disturbance and productivity to those between biological disturbance and productivity. Furthermore, to evaluate how these effects varied among different components of marine hard-substratum assemblages, analyses were done separately on algal and invertebrate richness, as well as richness of the whole assemblage. Physical disturbance (wave action) was simulated at five distinct frequencies, while biological disturbance (grazing periwinkles) was manipulated as present or absent, and productivity as high or ambient. Uni- and multivariate analyses both showed significant effects of physical disturbance and interactive effects between biological disturbance and productivity on the composition of assemblages and the total species richness. The algal richness was significantly affected by productivity and biological disturbance, whereas the invertebrate richness was affected by physical disturbance only. Thus, we show, for the first time, that biological disturbance and physical disturbance interact differently with productivity, because these two types of disturbance affect different components of assemblages. These patterns might be explained by differences in the distribution (i.e. press vs. pulse) and degree of selectivity between disturbances. Because different types of disturbance can affect different components of assemblages, general ecological models will benefit from using natural diverse communities and studies concerned with particular subsets of assemblages may be misleading. In conclusion, this study shows that the outcome of experiments on effects of disturbance and productivity on diversity is greatly influenced by the composition of the assemblage under study, as well as on the type of disturbance that is used as an experimental treatment.
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