| 1. |
- Erlandsson, Johan, et al.
(författare)
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Patchiness and Co-Existence of Indigenous and Invasive Mussels at Small Spatial Scales : The Interaction of Facilitation and Competition
- 2011
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Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 6:11, s. e26958-
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Tidskriftsartikel (refereegranskat)abstract
- Ecological theory predicts that two species with similar requirements will fail to show long-term co-existence in situations where shared resources are limiting, especially at spatial scales that are small relative to the size of the organisms. Two species of intertidal mussels, the indigenous Perna perna and the invasive Mytilus galloprovincialis, form mixed beds on the south coast of South Africa in a situation that has been stable for several generations of these species, even though these populations are often limited by the availability of space. We examined the spatial structure of these species where they coexist at small spatial scales in the absence of apparent environmental heterogeneity at two sites, testing: whether conspecific aggregation of mussels can occur (using spatial Monte-Carlo tests); the degree of patchiness (using Korcak B patchiness exponent), and whether there was a relationship between percent cover and patchiness. We found that under certain circumstances there is non-random conspecific aggregation, but that in other circumstances there may be random distribution (i.e. the two species are mixed), so that spatial patterns are context-dependent. The relative cover of the species differed between sites, and within each site, the species with higher cover showed low Korcak B values (indicating low patchiness, i.e. the existence of fewer, larger patches), while the less abundant species showed the reverse, i.e. high patchiness. This relationship did not hold for either species within sites. We conclude that co-existence between these mussels is possible, even at small spatial scales because each species is an ecological engineer and, while they have been shown to compete for space, this is preceded by initial facilitation. We suggest that a patchy pattern of co-existence is possible because of a balance between direct (competitive) and indirect (facilitative) interactions.
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| 2. |
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| 3. |
- Erlandsson, Johan, et al.
(författare)
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Recruit/algal interaction prevents recovery of overexploited mussel beds : Indirect evidence that post-settlement mortality structures mussel populations
- 2011
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Ingår i: Estuarine, Coastal and Shelf Science. - : Elsevier BV. - 0272-7714 .- 1096-0015. ; 92:1, s. 132-139
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Tidskriftsartikel (refereegranskat)abstract
- The mechanisms maintaining community structure following an ecosystem shift are poorly understood and we propose that they must inherently be biological. Over-exploitation can provide a natural experiment with man as a predator driving a change in community structure, possibly an ecosystem shift. We examined a possible mechanism that maintains algal beds as an alternative state on the east coast of South Africa where the mussel Perna perna has been overexploited. Even on unexploited shores, about 50% of mussel larvae settle onto algae, but it is unclear whether they later recruit into adult beds. On such shores we used two indirect field approaches to understand the fate of recruits, testing whether inhibition of mussel recruitment by macroalgae could constitute a biological mechanism preventing reversion from the algal to the pre-disturbance mussel-dominated state. First, we examined possible ontogenetic migration of recruits from algae to adult mussels, testing the prediction that the ratio large:small recruits in adult beds is greater where algae are liberally interspersed with mussels. Second, we examined whether, like adults, recruits show spatial structure that is related to the distribution of topographic depressions, testing the hypothesis that large and small recruits show different co-variation with depressions, microhabitats where algae commonly occur. We found no evidence that recruits on algae actively move to nearby mussel beds as neither the ratio large:small recruits nor the abundances of small or large recruits showed any relationship with algal cover/variability. Small and large recruits showed different co-variation with topographic depressions on spatially structured transects. Like adults, large recruits commonly exhibited negative relationships with depressions. Thus, large recruits neither occur on algae nor migrate from algae to the primary substratum or onto adult beds. Consequently our results (a) highlight the importance of post-settlement mortality in structuring these mussel populations, and (b) suggest that the interception of larvae by algae forms a biological mechanism that can maintain macroalgal beds that develop following exploitative disturbance by man, thus preventing or at least drastically delaying the natural recovery of mussel beds.
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| 4. |
- Erlandsson, Tina, et al.
(författare)
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Modeling fighter aircraft mission survivability
- 2011
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Ingår i: Proceedings of the 14th International Conference on Information Fusion (FUSION 2011). - New York : IEEE conference proceedings. - 9781457702679 - 1457702673 ; , s. 999-1006
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A fighter aircraft flying a mission is often exposed to ground-based threats such as surface-to-air missile (SAM) sites.The fighter pilot needs to take actions to minimize the risk of being shot down, but at the same time be able to accomplish the mission. In this paper we propose a survivability model, which describes the probability that the aircraft will be able to fly a given route without being hit by incoming missiles. Input to this model can consist of sensor measurements collected during flight as well as intelligence data gathered before the mission.This input is by nature uncertain and we therefore investigate the influence of uncertainty in the input to the model. Finally we propose a number of decision support functions that can be developed based on the suggested model such as countermeasure management, mission planning and sensor management
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| 5. |
- Erlandsson, Tina
(författare)
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Situation analysis for fighter aircraft combat survivability
- 2011
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Fighter pilots operate in environments where an erroneous decision may have fatal consequences. A tactical decision support system (TDSS) could aid the pilots to analyze the situation and make correct decisions. The TDSS can, for instance, highlight important information and suggest suitable actions. The aim of this thesis is to provide a situation analysis model of combat survival that can be utilized in a TDSS.The first part of this thesis describes an analysis of what the model needs to describe and how it can be used. It is concluded that the model should evaluate the outcome of different actions with respect to combat survival. This evaluation can guide the pilot’s decision making, so that actions leading to dangerous situations are avoided. The analysis also highlights the need of handling uncertainties, both measurement precision uncertainty regarding the locations and capabilities of the threats (enemies) and inference uncertainties regarding the prediction of how the threats will act.Finally, arguments for focusing the rest of the work on a single fighter aircraft and threats located on the ground are presented. The second part of the thesis suggests a model, which describes the survivability, i.e., the probability that the aircraft can fly a route without being hit by fire from ground-based threats. Thus, the model represents the inference uncertainty, since it describes the probability of survival. The model’s characteristics are discussed, e.g., that the model is implementable and can be adapted to describe different kinds of ground-based threats. Uncertainty in terms of measurement precision influences the estimate of the survivability. Two different ways of representing this is discussed: calculating the worst case scenario or describing the input as random variables and the resulting survivability as a random variable with a probability distribution. Monte Carlo simulations are used for estimating the distribution for survivability in a few illustrative scenarios, where the input is represented as random variables. The simulations show that when the uncertainty in input is large, the survivability distribution may be both multimodal and mixed. Two uncertainty measures are investigated that condense the information in the distributions into a single value: standard deviation and entropy. The simulations show that both of these measures reflect the uncertainty. Furthermore, the simulations indicate that the uncertainty measures can be used for sensor management, since they point out which information that is the most valuable to gather in order to decrease the uncertainty in the survivability.Finally, directions for future work are suggested. A number of TDSS functions that can be developed based on the model are discussed e.g., warnings, countermeasure management, route-planning and sensor management. The design of these functions could require extending the threat model to incorporate airborne threats and the effects of countermeasures. Further investigations regarding the uncertainty in the model are also suggested.
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| 7. |
- Jungerstam, Jennifer, et al.
(författare)
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Is habitat amount important for biodiversity in rocky shore systems? : A study of South African mussel assemblages
- 2014
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Ingår i: Marine Biology. - : Springer Science and Business Media LLC. - 0025-3162 .- 1432-1793. ; 161:7, s. 1507-1519
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Tidskriftsartikel (refereegranskat)abstract
- Habitat-forming species on rocky shores are often subject to high levels of exploitation, but the effects of subsequent habitat loss and fragmentation on associated species and the ecosystem as a whole are poorly understood. In this study, the effects of habitat amount on the fauna associated with mussel beds were investigated, testing for the existence of threshold effects at small landscape scales. Specifically, the relationships between mussel or algal habitat amount and: associated biodiversity, associated macrofaunal abundance and density of mussel recruits were studied at three sites (Kidd's Beach, Kayser's Beach and Kini Bay) on the southern and south-eastern coasts of South Africa. Samples, including mussel-associated macrofauna, of 10 x 10 cm were taken from areas with 100 % mussel cover (Perna perna or a combination of P. perna and Mytilus galloprovincialis) at each site. The amount of habitat provided by mussels and algae surrounding the sampled areas was thereafter determined at the 4.0 m(2) scale. A number of significant positive relationships were found between the amount of surrounding mussel habitat and the abundances of several taxa (Anthozoa, Malacostraca and Nemertea). Likewise, there were positive relationships between the amount of surrounding algal habitat and total animal abundance as well as abundance of mussel recruits at one site, Kini Bay. In contrast, abundance of mussel recruits showed a significant negative relationship with the amount of mussel habitat at Kayser's Beach. Significant negative relationships were also detected between the amount of mussel habitat and species richness and total abundance at Kidd's Beach, and between amount of mussel habitat and the abundance of many taxa (Bivalvia, Gastropoda, Maxillopoda, Ophiuroidea, Polychaeta and Pycnogonida) at all three sites. No threshold effects were found, nor were significant relationships consistent across the investigated sites. The results indicate that the surrounding landscape is important in shaping the structure of communities associated with these mussel beds, with significant effects of the amount of surrounding habitat per se. The strength and the direction of habitat effects vary, however, between shores and probably with the scale of observation as well as with the studied dependent variables (e.g. diversity, abundance, mussel recruitment, species identity), indicating the complexity of the processes structuring macrofaunal communities on these shores.
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| 8. |
- Ludford, Adam, et al.
(författare)
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Testing source-sink theory : the spill-over of mussel recruits beyond marine protected areas
- 2012
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Ingår i: Landscape Ecology. - : Springer Science and Business Media LLC. - 0921-2973 .- 1572-9761. ; 27:6, s. 859-868
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Tidskriftsartikel (refereegranskat)abstract
- Source-sink theory has contributed to our understanding of the function of protected areas, particularly due to their role as population sources. Marine reserves are a preferred management tool for the conservation of natural populations, creating areas of good quality habitat and thus improving population connectivity by enhancing larval supply and recruitment among shores. Despite recent advances in the study of protected areas in the context of the source-sink theory, rigorous and empirical testing of marine reserves as metapopulation sources for the adjacent areas remain largely unexplored. We investigated the role of marine reserves as population sources, whether there was spill-over beyond the reserve boundaries and if so, whether spill-over was directional. We measured percentage cover and recruitment of mussels (Perna perna) at two reserves and two comparably sized exploited control areas on the south-east coast of South Africa where unprotected populations are severely affected by artisanal exploitation. Adult abundances were enhanced within reserves, but decreased towards their edges. We predicted that recruitment would mirror adult abundances and show directionality, with northern shores having greater recruitment following the prevalent northward flow of near-shore currents. There were, however, no correlations between adult abundances and recruitment for any months or shores, and no clear spatial patterns in recruitment (i.e. similar patterns occurred at reserves and controls). The results emphasise that, while reserves may act as important refuges by protecting adult abundances, their influence on promoting recovery of near-by exploited shores through larval spill-over may be overestimated.
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| 9. |
- Mtwana Nordlund, Lina, et al.
(författare)
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Intertidal Zone Management in the Western Indian Ocean : Assessing Current Status and Future Possibilities Using Expert Opinions
- 2014
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Ingår i: Ambio. - : Springer Science and Business Media LLC. - 0044-7447 .- 1654-7209. ; 43:8, s. 1006-1019
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Tidskriftsartikel (refereegranskat)abstract
- This expert opinion study examined the current status of the intertidal zone in the Western Indian Ocean (WIO) and ranked and discussed future management approaches. Information was gathered from scientists, practitioners, and managers active in the WIO region through a questionnaire and a workshop. The experts stated that the productive intertidal environment is highly valuable for reasons such as recreation, erosion protection, and provision of edible invertebrates and fish. Several anthropogenic pressures were identified, including pollution, harbor activities, overexploitation, and climate change. The experts considered the WIO intertidal zone as generally understudied, undermanaged, and with poor or no monitoring. The most important management strategies according to the expert opinions are to develop and involve local people in integrated coastal zone management (ICZM), to increase knowledge on species-environment relationships, and to develop awareness campaigns and education programs. To improve coastal environmental management and conservation, we argue that the intertidal zone should be treated as one organizational management unit within the larger framework of ICZM.
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| 10. |
- Nordlund, Lina, 1979-, et al.
(författare)
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Changes in an East African social-ecological seagrass system : invertebrate harvesting affecting species composition and local livelihood
- 2010
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Ingår i: Aquatic Living Resources. - : EDP Sciences. - 0990-7440 .- 1765-2952. ; 23:4, s. 399-416
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Tidskriftsartikel (refereegranskat)abstract
- Seagrass meadows support high biodiversity and are important for invertebrate harvesting activities in developing countries. The aim of this study was to estimate the social and ecological effects of invertebrate harvesting, i.e. how this exploitation may affect/has affected seagrass variables (biomass, shoot density and canopy height), macrofaunal community structure, the use and importance of these resources for the livelihood of local people over time. A multi-disciplinary approach was used, including interviews with harvesters, observations of the number/activities of invertebrate harvesters, and a biological field study in Zanzibar, Tanzania. The study showed that women/children harvest invertebrates, and they prefer large seagrass patches, high to medium shoot density, and high seagrass cover. All interviewees said they had noticed a decline in seagrass distribution over the last decade, >20% considered it a large decline. Interviewees also reported decreased numbers of animals, but no change in the number of animal species over the last decade. The main reasons for the decline of seagrass and animals according to interviewees, are an increase in the number of harvesters, and a change in attitude, i.e. people being less careful about the intertidal zone and seagrasses. Invertebrate harvesting was found important for food security and provision of cash income. The current average catch weight was ca. 2 kg/collection day/person, and 3 kg and 5 kg, 5–10 and 30 years ago respectively according to interviewees. At present, the harvesting women earn ca 60–70% and ca 40% of what they would have if catches were the same sizes as they were 5–10 and 30 years ago respectively, according to our calculations. The field sampling within seagrass beds showed that an inaccessible/remote site had significantly higher invertebrate abundance and species richness/diversity than an exploited site (ANOVA). Multivariate statistics further revealed weak but significant differences for animal abundance and biomass between these sites. By combining findings from both interviews and field sampling this study shows that invertebrate harvesters can influence macrofaunal community structure in seagrass meadows, which in turn results in negative impacts on local harvesters’ economy and livelihood.
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| 11. |
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| 12. |
- Temnerud, Johan, et al.
(författare)
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Can the distribution of headwater stream chemistry be predicted from downstream observations?
- 2010
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Ingår i: Hydrological Processes. - : Wiley. - 0885-6087 .- 1099-1085. ; 24:16, s. 2269-2276
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Tidskriftsartikel (refereegranskat)abstract
- Small streams with catchment areas <2 km(2) make up the majority of all stream length and are of great ecological importance. Surveys of first and second order streams reveal great spatial and temporal variability in the water chemistry of these headwaters, but their assessment presents a serious challenge since systematic, representative data are usually only collected in larger streams and rivers. Using low flow synoptic survey data from seven mesoscale Swedish catchments, this study tests the hypothesis that downstream monitoring data can be used to predict key features of the distribution of chemistry in headwater streams [median and interquartile range (IQR)]. Three ecologically relevant analytes were tested: pH, acid neutralizing capacity (ANC) and total organic carbon (TOC). For all seven catchments, the outlets (36-127 km(2)) were considerably less acid with lower TOC than the median of the headwaters (<2 km(2), N = 19-45). Among catchments, headwater median and IQR were positively correlated with the value at the outlet, for all three analytes. A univariate general linear model (GLM) was used to predict the headwater chemistry distribution for each catchment from its outlet chemistry, using the relationship established with the other six catchments. Headwater median pH and IQR of ANC were well predicted by a single downstream sample [median adj. R-2 similar to 0.7, normalized root mean squared error (NRMSE) <0.7]. Other response variables were not as well predicted, with median adj. R-2 ranging from 0.08 to 0.48, and NRMSE up to 1.1. A minority of models were significant at alpha = 0.05, in part due to the limited availability of catchments with such extensive survey data. However, the clear trends observed suggest that with additional model development, downstream chemistry could ultimately provide a valuable tool for characterizing the range of chemistry in the contributing headwaters. Copyright (C) 2010 John Wiley & Sons, Ltd.
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