| 1. |
- Duffy, J. E., et al.
(författare)
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Biodiversity mediates top-down control in eelgrass ecosystems: a global comparative-experimental approach
- 2015
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Ingår i: Ecology Letters. - : Wiley. - 1461-023X .- 1461-0248. ; 18:7, s. 696-705
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Tidskriftsartikel (refereegranskat)abstract
- Nutrient pollution and reduced grazing each can stimulate algal blooms as shown by numerous experiments. But because experiments rarely incorporate natural variation in environmental factors and biodiversity, conditions determining the relative strength of bottom-up and top-down forcing remain unresolved. We factorially added nutrients and reduced grazing at 15 sites across the range of the marine foundation species eelgrass (Zostera marina) to quantify how top-down and bottom-up control interact with natural gradients in biodiversity and environmental forcing. Experiments confirmed modest top-down control of algae, whereas fertilisation had no general effect. Unexpectedly, grazer and algal biomass were better predicted by cross-site variation in grazer and eelgrass diversity than by global environmental gradients. Moreover, these large-scale patterns corresponded strikingly with prior small-scale experiments. Our results link global and local evidence that biodiversity and top-down control strongly influence functioning of threatened seagrass ecosystems, and suggest that biodiversity is comparably important to global change stressors.
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| 2. |
- Gross, C. P., et al.
(författare)
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The biogeography of community assembly: latitude and predation drive variation in community trait distribution in a guild of epifaunal crustaceans
- 2022
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Ingår i: Proceedings of the Royal Society B: Biological Sciences. - : The Royal Society. - 1471-2954 .- 0962-8452. ; 289:1969
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Tidskriftsartikel (refereegranskat)abstract
- While considerable evidence exists of biogeographic patterns in the intensity of species interactions, the influence of these patterns on variation in community structure is less clear. Studying how the distributions of traits in communities vary along global gradients can inform how variation in interactions and other factors contribute to the process of community assembly. Using a model selection approach on measures of trait dispersion in crustaceans associated with eelgrass (Zostera marina) spanning 30° of latitude in two oceans, we found that dispersion strongly increased with increasing predation and decreasing latitude. Ocean and epiphyte load appeared as secondary predictors; Pacific communities were more overdispersed while Atlantic communities were more clustered, and increasing epiphytes were associated with increased clustering. By examining how species interactions and environmental filters influence community structure across biogeographic regions, we demonstrate how both latitudinal variation in species interactions and historical contingency shape these responses. Community trait distributions have implications for ecosystem stability and functioning, and integrating large-scale observations of environmental filters, species interactions and traits can help us predict how communities may respond to environmental change.
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| 3. |
- Reynolds, P., et al.
(författare)
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Latitude, temperature and habitat complexity predict predation pressure in eelgrass beds across the Northern Hemisphere
- 2018
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Ingår i: Ecology. - : Wiley. - 0012-9658 .- 1939-9170. ; 99:1, s. 29-35
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Tidskriftsartikel (refereegranskat)abstract
- Latitudinal gradients in species interactions are widely cited as potential causes or consequences of global patterns of biodiversity. However, mechanistic studies documenting changes in interactions across broad geographic ranges are limited. We surveyed predation intensity on common prey (live amphipods and gastropods) in communities of eelgrass (Zostera marina) at 48 sites across its Northern Hemisphere range, encompassing over 370 of latitude and four continental coastlines. Predation on amphipods declined with latitude on all coasts but declined more strongly along western ocean margins where temperature gradients are steeper. Whereas in situ water temperature at the time of the experiments was uncorrelated with predation, mean annual temperature strongly positively predicted predation, suggesting a more complex mechanism than simple increased metabolic activity at the time of predation. This large-scale biogeographic pattern was modified by local habitat characteristics; predation declined with higher shoot density both among and within sites. Predation rates on gastropods, by contrast, were uniformly low and varied little among sites. The high replication and geographic extent of our study not only provides additional evidence to support biogeographic variation in intensity, but also insight into the mechanisms that relate temperature and biogeographic gradients in species interactions.
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| 4. |
- Alonso Aller, Elisa, et al.
(författare)
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Fishing weakens a positive link between herbivore abundance and plant growth in tropical seagrass beds
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Herbivory is a key process influencing the structure and function of both terrestrial and aquatic systems. In seagrass ecosystems, moderate levels of herbivory may stimulate plant growth, compensating for the loss of eaten tissue. However, the relationship between herbivory and seagrass growth can be influenced by an array of factors, such as seasonality, herbivore abundance, and presence of epiphytes, many of which can be directly or indirectly affected by human activities like fishing. Here, we used data from a multi-season field survey in fished and protected seagrass beds to assess how fishing and seasonality affect the link between herbivores, herbivory, and plant growth in seagrasses. Path analyses revealed an interactive effect of seasonality and protection. In protected seagrass beds, seasonally high herbivore abundance positively affected herbivory rates, which in turn enhanced seagrass growth. This link was however not apparent in seagrass beds subjected to fishing activities. At the same time, seasonality effects seemed stronger in fished areas, suggesting that in addition to weakening a positive herbivory-plant growth interaction, fishing increases temporal instability of ecosystems. Our results highlight the need for evaluating not only the direct effects of fisheries exploitation on fish populations, but also the potential indirect effects on ecosystems, to improve fisheries management.
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| 5. |
- Alonso Aller, Elisa, et al.
(författare)
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Marine protected areas increase temporal stability of community structure, but not density or diversity, of tropical seagrass fish communities
- 2017
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Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 12:8
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Tidskriftsartikel (refereegranskat)abstract
- Marine protected areas (MPAs) have been shown to increase long-term temporal stability of fish communities and enhance ecosystem resilience to anthropogenic disturbance. Yet, the potential ability of MPAs to buffer effects of environmental variability at shorter time scales remains widely unknown. In the tropics, the yearly monsoon cycle is a major natural force affecting marine organisms in tropical regions, and its timing and severity are predicted to change over the coming century, with potentially severe effects on marine organisms, ecosystems and ecosystem services. Here, we assessed the ability of MPAs to buffer effects of monsoon seasonality on seagrass-associated fish communities, using a field survey in two MPAs (no-take zones) and two unprotected (open-access) sites around Zanzibar (Tanzania). We assessed the temporal stability of fish density and community structure within and outside MPAs during three monsoon seasons in 2014-2015, and investigated several possible mechanisms that could regulate temporal stability. Our results show that MPAs did not affect fish density and diversity, but that juvenile fish densities were temporally more stable within MPAs. Second, fish community structure was more stable within MPAs for juvenile and adult fish, but not for subadult fish or the total fish community. Third, the observed effects may be due to a combination of direct and indirect (seagrass-mediated) effects of seasonality and, potentially, fluctuating fishing pressure outside MPAs. In summary, these MPAs may not have the ability to enhance fish density and diversity and to buffer effects of monsoon seasonality on the whole fish community. However, they may increase the temporal stability of certain groups, such as juvenile fish. Consequently, our results question whether MPAs play a general role in the maintenance of biodiversity and ecosystem functioning under changing environmental conditions in tropical seagrass fish communities.
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| 6. |
- Austin, Åsa, 1988-
(författare)
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Aquatic vegetation in coastal ecosystems : The role of biotic interactions and environmental change for ecosystem functions and resilience in the Baltic Sea
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Coastal ecosystems are among the most productive on Earth but subjected to many human pressures. In shallow coastal areas, aquatic vegetation constitutes foundation species that sustain secondary production and act as a nutrient filter, which may buffer human impacts. But little is known about how anthropogenic factors alter biotic interactions in aquatic vegetation, and how these changes affect ecosystem functions and resilience.The aim of this thesis was to investigate how natural and anthropogenic factors alter aquatic vegetation communities and biotic interactions, and how these in turn affect ecosystem functions and resilience to common stressors. Shallow coastal bays in the Baltic Sea were used as model system. A large field survey was conducted to investigate effects of natural and anthropogenic gradients, including bay topographic openness and nutrient runoff, on vegetation communities and ecosystem functions. Results suggest that high vegetation cover can improve water clarity, whereas sediment-driven turbidity can negatively affect vegetation by decreasing the light penetration of the water (Paper I). This dual relationship indicates the potential for two alternative, self-sustaining states in shallow bays; with or without vegetation.Using data from the same survey I investigated the influence of species richness and cover of rooted aquatic vegetation and drift wrack (Fucus vesiculosus), for ecosystem multifunctionality (MF) (Paper II). MF was estimated as the mean of four variables used as proxies for key functions; large predatory fish recruitment, grazer biomass, inverted ‘nuisance’ algal biomass and water clarity. MF was highest when the two functionally different vegetation types (rooted and drifting) co-occurred at high covers, and high species richness increased multifunctionality by increasing rooted vegetation cover.To understand in greater detail if and how interactions within and between vegetation species mediate the effects of environmental change, I conducted two experiments. First, a cage experiment to test if intraspecific plant facilitation may buffer effects of altered top-down and bottom-up control (Paper III), then a mesocosm experiment to test if shading alters interspecific interactions between three common plant species (Paper IV). The cage experiment showed that high shoot density of a common plant (Myriophyllum spicatum) increased individual shoot performance, but only when subjected to both fertilization and large predatory fish exclusion (Paper III). The mesocosm experiment showed that individual species’ traits had stronger effect than shading on interspecific competition and community yield (Paper IV).In conclusion, my thesis shows that single and multiple ecosystem functions benefit from high vegetation cover, with direct and indirect effects of diversity, but are sensitive to anthropogenic stressors (Papers I, II). Further, shading alters biotic interactions among vegetation species in a eutrophic coastal ecosystem by increasing the competitive advantage of dominant species (Paper IV), while intraspecific facilitation increases resilience to interacting stressors (Paper III). Together, the results highlight the need for ecosystem-based management where efforts to reduce anthropogenic influence (e.g. by nutrient reduction and fishing restrictions) are combined with improved protection and restoration of the ecologically and economically valuable aquatic vegetation communities.
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| 7. |
- Austin, Åsa N., et al.
(författare)
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Synergistic Effects of Rooted Aquatic Vegetation and Drift Wrack on Ecosystem Multifunctionality
- 2021
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Ingår i: Ecosystems (New York. Print). - : Springer Science and Business Media LLC. - 1432-9840 .- 1435-0629. ; 24:7, s. 1670-1686
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Tidskriftsartikel (refereegranskat)abstract
- Ecosystem multifunctionality is an increasingly popular concept used to approximate multifaceted ecosystem functioning, which in turn may help advance ecosystem-based management. However, while experimental studies have shown a positive effect of diversity on multifunctionality, observational studies from natural systems-particularly aquatic-are scarce. Here, we tested the relative importance of species richness and cover of rooted aquatic vegetation, as well as cover of the loose-lying form of the macroalgae bladderwrack (Fucus vesiculosus), for ecosystem multifunctionality in shallow bays along the western Baltic Sea coast. We estimated multifunctionality based on four indicators of functions that support ecosystem services: recruitment of large predatory fish, grazer biomass, inverted 'nuisance' algal biomass, and water clarity. Piecewise path analysis showed that multifunctionality was driven by high cover of rooted aquatic vegetation and bladderwrack, particularly when the two co-occurred. This synergistic effect was nearly three times as strong as a negative effect of land-derived nitrogen loading. Species richness of aquatic vegetation indirectly benefitted multifunctionality by increasing vegetation cover. Meanwhile, high bladderwrack cover tended to decrease vegetation species richness, indicating that bladderwrack has both positive and negative effects on multifunctionality. We conclude that managing for dense and diverse vegetation assemblages may mitigate effects of anthropogenic pressures (for example, eutrophication) and support healthy coastal ecosystems that provide a range of benefits. To balance the exploitation of coastal ecosystems and maintain their multiple processes and services, management therefore needs to go beyond estimation of vegetation cover and consider the diversity and functional types of aquatic vegetation.
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| 8. |
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| 9. |
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| 10. |
- Gloster, Tracey M., et al.
(författare)
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Characterization and three-dimensional structures of two distinct bacterial xyloglucanases from families GH5 and GH12
- 2007
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Ingår i: Journal of Biological Chemistry. - 0021-9258 .- 1083-351X. ; 282:26, s. 19177-19189
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Tidskriftsartikel (refereegranskat)abstract
- The plant cell wall is a complex material in which the cellulose microfibrils are embedded within a mesh of other polysaccharides, some of which are loosely termed hemicellulose. One such hemicellulose is xyloglucan, which displays a beta-1,4-linked D-glucose backbone substituted with xylose, galactose, and occasionally fucose moieties. Both xyloglucan and the enzymes responsible for its modification and degradation are finding increasing prominence, reflecting both the drive for enzymatic biomass conversion, their role in detergent applications, and the utility of modified xyloglucans for cellulose fiber modification. Here we present the enzymatic characterization and three-dimensional structures in ligand free and xyloglucan- oligosaccharide complexed forms of two distinct xyloglucanases from glycoside hydrolase families GH5 and GH12. The enzymes, Paenibacillus pabuli XG5 and Bacillus licheniformis XG12, both display open active center grooves grafted upon their respective (beta/alpha)(8) and beta-jelly roll folds, in which the side chain decorations of xyloglucan may be accommodated. For the beta-jelly roll enzyme topology of GH12, binding of xylosyl and pendant galactosyl moieties is tolerated, but the enzymeis similarly competent in the degradation of unbranched glucans. In the case of the (beta/alpha)(8) GH5 enzyme, kinetically productive interactions are made with both xylose and galactose substituents, as reflected in both a high specific activity on xyloglucan and the kinetics of a series of aryl glycosides. The differential strategies for the accommodation of the side chains of xyloglucan presumably facilitate the action of these microbial hydrolases in milieus where diverse and differently substituted substrates may be encountered.
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