| 1. |
- Eros, Tibor, et al.
(författare)
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Forest-Stream linkages : Effects of Terrestrial Invertebrate Input and Light on Diet and Growth of Brown Trout (Salmo trutta) in a Boreal Forest Stream
- 2012
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Ingår i: PLOS ONE. - San Francisco, CA, USA : Public library science. - 1932-6203. ; 7:5, s. 1-11
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Tidskriftsartikel (refereegranskat)abstract
- Subsidies of energy and material from the riparian zone have large impacts on recipient stream habitats. Human-induced changes, such as deforestation, may profoundly affect these pathways. However, the strength of individual factors on stream ecosystems is poorly understood since the factors involved often interact in complex ways. We isolated two of these factors, manipulating the flux of terrestrial input and the intensity of light in a 2 x 2 factorial design, where we followed the growth and diet of two size-classes of brown trout (Salmo trutta) and the development of periphyton, grazer macroinvertebrates, terrestrial invertebrate inputs, and drift in twelve 20 m long enclosed stream reaches in a five-monthlong experiment in a boreal coniferous forest stream. We found that light intensity, which was artificially increased 2.5 times above ambient levels, had an effect on grazer density, but no detectable effect on chlorophyll a biomass. We also found a seasonal effect on the amount of drift and that the reduction of terrestrial prey input, accomplished by covering enclosures with transparent plastic, had a negative impact on the amount of terrestrial invertebrates in the drift. Further, trout growth was strongly seasonal and followed the same pattern as drift biomass, and the reduction of terrestrial prey input had a negative effect on trout growth. Diet analysis was consistent with growth differences, showing that trout in open enclosures consumed relatively more terrestrial prey in summer than trout living in covered enclosures. We also predicted ontogenetic differences in the diet and growth of old and young trout, where we expected old fish to be more affected by the terrestrial prey reduction, but we found little evidence of ontogenetic differences. Overall, our results showed that reduced terrestrial prey inputs, as would be expected from forest harvesting, shaped differences in the growth and diet of the top predator, brown trout.
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| 2. |
- Gustafsson, Oskar, 1990-, et al.
(författare)
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Bayesian optimization of hyperparameters from noisy marginal likelihood estimates
- 2023
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Ingår i: Journal of applied econometrics (Chichester, England). - : Wiley. - 0883-7252 .- 1099-1255. ; 38:4, s. 577-595
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Tidskriftsartikel (refereegranskat)abstract
- Bayesian models often involve a small set of hyperparameters determined by maximizing the marginal likelihood. Bayesian optimization is an iterative method where a Gaussian process posterior of the underlying function is sequentially updated by new function evaluations. We propose a novel Bayesian optimization framework for situations where the user controls the computational effort and therefore the precision of the function evaluations. This is a common in econometrics where the marginal likelihood is often computed by Markov chain Monte Carlo or importance sampling methods. The new acquisition strategy gives the optimizer the option to explore the function with cheap noisy evaluations and therefore find the optimum faster. The method is applied to estimating the prior hyperparameters in two popular models on US macroeconomic time series data: the steady-state Bayesian vector autoregressive (BVAR) and the time-varying parameter BVAR with stochastic volatility.
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| 3. |
- Gustafsson, Pär, 1973-, et al.
(författare)
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Effects of woody debris and the supply of terrestrial invertebrates on the diet and growth of brown trout (Salmo trutta) in a boreal stream
- 2014
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Ingår i: Freshwater Biology. - : John Wiley & Sons. - 0046-5070 .- 1365-2427. ; 59:12, s. 2488-2501
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Tidskriftsartikel (refereegranskat)abstract
- Changes to the riparian vegetation of forest streams during timber harvesting may have considerable impacts on stream biota, but few studies have attempted to separate the effects of individual factors that are altered during clear-felling operations.We studied the effects of large wood and terrestrial invertebrate supply, two factors affected by forest harvesting, on the growth and diet of two size classes of brown trout (Salmo trutta) during a two-month (June–August) field enclosure experiment. Twelve 20-m-long enclosed stream reaches were used in a 2 × 2 factorial design, with large wood either absent or added to mimic pre-modern forestry conditions, and terrestrial invertebrate inputs either reduced or maintained at ambient levels.The addition of large wood had a positive effect on the growth of large trout but no effect on small trout, whereas terrestrial invertebrate input had no effect on the growth of either size class. Growth rates were highest in the treatment with ambient terrestrial invertebrate inputs and added wood, were lowest in the treatment with reduced terrestrial invertebrate inputs and no added wood and were intermediate in the other two treatments.Dietary analyses showed no difference in treatments with and without added wood, perhaps because instream wood influences growth by producing profitable stream positions for trout, rather than by acting as a source of prey. Terrestrial invertebrate inputs affected the diet, as trout in enclosures with reduced inputs had a lower proportion of terrestrial invertebrate biomass in the diet than trout in enclosures with ambient terrestrial inputs.Our results suggest that leaving woody debris in streams when harvesting forests may enhance trout growth and that this is probably due to the physical changes in depth and current velocity caused by the wood rather than to changes in dietary prey composition.
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| 4. |
- Gustafsson, Pär, 1973-
(författare)
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Forest – stream linkages : Brown trout (Salmo trutta) responses to woody debris, terrestrial invertebrates and light
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Forests surrounding streams affect aquatic communities in numerous ways, contributing to energy fluxes between terrestrial and lotic ecosystems. The five papers in this thesis focus on woody debris, terrestrial invertebrates and light, three factors influenced by riparian zone structure, potentially affecting streams and brown trout (Salmo trutta). The individual strength of these stressors and their interactions with each other are not well studied, and their qualitative effects may differ both spatially and temporally as well as with the size-structure of specific fish populations. Using a combination of laboratory and field experiments, I examined the effects of woody debris, terrestrial invertebrates and light on prey availability and on the growth rates, diets and behavior of different size-classes of trout. My field experiments showed that addition of high densities of large wood affected trout growth in a positive way. This positive effect of large wood on trout growth may be related to prey abundance, as indicated by the high standing crop of aquatic macroinvertebrates on the wood. The positive effects on trout may also be related to decreased energy expenditures in wood habitats, as trout increased the ratio between numbers of prey captured and time spent active and that swimming activity and level of aggression decreased as wood densities were increased in a laboratory experiment. Terrestrial invertebrates are generally assumed to be a high quality prey resource for fish and my field experiments showed that reduction of terrestrial invertebrate inputs had a negative effect on trout growth. The availability of terrestrial prey in the stream was also coupled to trout diet and linked to growth, as fish with high growth rates had high proportions of terrestrial prey in their diets. Light, measured as PAR, did not have an effect on chlorophyll biomass, nor was there an effect on aquatic macroinvertebrates or trout. Hence, even if light levels were sufficient for increased photosynthesis, other factors such as low nutrient content may have limited the effects. Many of my results were dependent on fish-size. I observed, for example, that large trout had higher capture rates on surface-drifting terrestrial prey than small trout when prey densities were intermediate or high, but at low prey densities, the consumption of terrestrial prey by large and small trout were similar. Moreover, although large wood and terrestrial invertebrates affected growth of both small and large trout, the effects were generally more consistent for large trout. Although changes in riparian forests typically induce an array of interacting effects that certainly call for further research, the overall conclusion from this thesis is that many of the factors I have studied have profound effects on stream biota and trout. The positive effects from large wood also propose that adding trees to streams may partly compensate for negative effects associated with riparian deforestation.
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| 5. |
- Gustafsson, Pär, 1973-
(författare)
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Forest-stream linkages : Experimental studies of foraging and growth of brown trout (Salmo trutta L).
- 2008
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Riparian vegetation along streams and rivers affects the aquatic community in numerous ways and often operates as a link for energy flux between forest and streams. The studies presented in this licentiate thesis focus on light and terrestrial invertebrates, two factors influenced by riparian zone structure, which potentially affect stream ecosystems and thus also brown trout (Salmo trutta). Paper I is a laboratory experiment where I study size dependent foraging behavior on surface-drifting terrestrial invertebrates and benthic invertebrates by brown trout. The results show a size-dependent difference in foraging ability with large trout being better able to use terrestrial surface prey than small trout. I argue that such ontogenetic foraging differences are due to both morphological constraints (eg. gape limitation) and size dependent behavioral differences related to predation risk. Paper II consists of a 5 month-long 2x2 factorial design field experiment where my objective was to examine the effects of terrestrial invertebrate input and solar radiation (PAR) on different trophic levels in a boreal headwater stream. More specifically, I followed the effects of increased light and decreased terrestrial invertebrate subsidies on periphyton, benthic macroinvertebrates and two size classes of the top fish predator, brown trout. The results showed that the reduction of terrestrial invertebrate input had size- and seasonal-dependent effects on trout, where large trout had lower growth rates than small trout, mainly in summer. Diet analyses of trout supported growth differences in that large trout in unmanipulated enclosures consumed relatively more terrestrial prey than large trout living in enclosures with reduced terrestrial inputs. A higher reliance on terrestrial prey subsidies by large trout compared to small may be explained by ontogenetic differences in foraging and habitat choice. Despite a 2.5-fold increase in PAR, light did not have an effect on chlorophyll a biomass, nor was there an effect on the density or composition of benthic macroinvertebrates. The lack of effects on primary production may be explained by very low nutrient levels in the stream.
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| 6. |
- Gustafsson, Pär, 1973-, et al.
(författare)
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Functional response and size-dependent foraging on aquatic and terrestrial prey by brown trout (Salmo trutta L.)
- 2010
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Ingår i: Ecology of Freshwater Fish. - : Wiley. - 0906-6691 .- 1600-0633. ; 19:2, s. 170-177
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Tidskriftsartikel (refereegranskat)abstract
- Terrestrial invertebrate subsidies are believed to be important energy sources for drift-feeding salmonids. Despite this, size-specific use of and efficiency in procuring this resource have not been studied to any great extent. Therefore, we measured the functional responses of three size classes of wild brown trout Salmo trutta (0+, 1+ and ≥2+) when fed either benthic- (Gammarus sp.) or surface-drifting prey (Musca domestica) in laboratory experiments. To test for size-specific prey preferences, both benthic and surface prey were presented simultaneously by presenting the fish with a constant density of benthic prey and a variable density of surface prey. The results showed that the functional response of 0+ trout differed significantly from the larger size classes, with 0+ fish having the lowest capture rates. Capture rates did not differ significantly between prey types. In experiments when both prey items were presented simultaneously, capture rate differed significantly between size classes, with larger trout having higher capture rates than smaller trout. However, capture rates within each size class did not change with prey density or prey composition. The two-prey experiments also showed that 1+ trout ate significantly more surface-drifting prey than 0+ trout. In contrast, there was no difference between 0+ and ≥2+ trout. Analyses of the vertical position of the fish in the water column corroborated size-specific foraging results: larger trout remained in the upper part of the water column between attacks on surface prey more often than smaller trout, which tended to seek refuge at the bottom between attacks. These size-specific differences in foraging and vertical position suggest that larger trout may be able to use surface-drifting prey to a greater extent than smaller conspecifics.
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| 7. |
- Gustafsson, Pär, 1973-, et al.
(författare)
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The influence of large wood on brown trout (Salmo trutta) behaviour and surface foraging
- 2012
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Ingår i: Freshwater Biology. - : Wiley. - 0046-5070 .- 1365-2427. ; 57:5, s. 1050-1059
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Tidskriftsartikel (refereegranskat)abstract
- 1. Changes in riparian vegetation owing to forest harvesting may affect the input of large wood, a major structural element, to streams. Studies of large wood impacts on stream fish have focused on population-level responses, whereas little attention has been given to how wood affects fish behaviour.2. In a laboratory stream experiment, we tested how two size classes of brown trout, Salmo trutta, (mean size of 85 and 125 mm), alone and together, responded to a gradient of large wood in terms of activity, foraging on terrestrial drift and interactions between conspecifics.3. The results showed that the presence of large wood significantly reduced the overall activity of the fish, the number of agonistic interactions between individuals and the proportion of captured prey. However, activity decreased relatively more than the proportion of captured prey, resulting in a significant positive net effect of wood on the number of prey captures per time spent active (PTA). This indicates that trout living in habitats with high wood density may have a higher net energy gain than trout living in habitats with less wood.4. There were no observable size-class differences in the benefits of large wood or in the utilisation of surface-drifting terrestrial prey.5. These results suggest that the presence of large wood may be an important factor shaping stream communities and that a lack of structural complexity may decrease energy gain, increase agonistic interactions and, consequently, lower the production of brown trout
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| 8. |
- Gustafsson, Pär, 1973-, et al.
(författare)
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Woody debris and terrestrial invertebrates : effects on prey resourses for brown trout (Salmo trutta) in a boreal stream
- 2014
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Ingår i: Environmental Biology of Fishes. - : Springer Science and Business Media LLC. - 0378-1909 .- 1573-5133. ; 97:5, s. 529-542
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Tidskriftsartikel (refereegranskat)abstract
- Intensive forestry and other activities that alter riparian vegetation may disrupt the connectivity and the flux of energy between terrestrial and aquatic habitats and have large effects on biota, especially in small streams. We manipulated the amount of in-stream wood and the flux of terrestrial invertebrate subsidies to determine how these factors affected potential food resources for drift-feeding brown trout (Salmo trutta ) in a boreal Swedish forest stream. Specifically, we followed the effects on the abundance of aquatic and terrestrial invertebrate fauna from June to August 2007. The treatments were 1) addition of wood, unmanipulated terrestrial invertebrate inputs, 2) reduction of terrestrial invertebrate inputs (using canopy covers), no addition of wood, 3) unmanipulated ambient conditions, 4) simultaneous addition of wood and reduction of terrestrial invertebrate inputs. Added wood resulted in greater biomass of aquatic invertebrate biomass, and both input and drift of terrestrial invertebrates were reduced by canopy covers. In terms of total potential prey biomass, the addition of wood with ambient levels of terrestrial invertebrate inputs had the highest standing crop of benthic, wood-living and terrestrial invertebrates combined, whereas the treatment with reduced terrestrial input and no wood added had the lowest standing crop. Our study indicates that forest practices that both reduce the recruitment of wood and the input of terrestrial invertebrates to small streams have negative effects on prey availability for drift-feeding brown trout. The positive effects of wood addition on biomass of aquatic macroinvertebrates may partly compensate for the negative effects of reduced terrestrial invertebrate subsidies.
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| 9. |
- Kougioumtzis, Konstantin, 1966, et al.
(författare)
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Is there a generic ball ability? An empirical study of measuring and modeling performance on 12 ball tasks : ¿Hay una habilidad de pelota genérica? Un estudio empírico del rendimiento de medición y modelado en 12 tareas de pelota.
- 2018
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Ingår i: Cubamotricidad 2018. For a Physical Culture of Piece. 22-26/10. Palacio del Conventiones, La Habana, Cuba.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Understanding the complexity of motor abilities and skills is a sine qua non for a scientific approach to processes of diagnosis, prediction and program evaluation in human movement and sport performance. However, there is a general paucity of research that seeks to identify the complexity of motor abilities and movement skills in tasks when a ball is involved. Aiming at a contribution towards the formation of a solid evidence basis, this article investigates the interrelationship among performances in various ball tasks. Utilizing a special constructed and technologically enhanced instrument, it is hypothetised that the commonalities of the objectively measured outcomes supports the notion of an underlying generic ball ability. 213 participants were tested in the 12 ball tasks of the instrument (racket juggle, elbow juggle, handwall, footwall, ball machine, knee juggle, board bouncing, bat balancing, roller coaster, foot rolling, tube drop, stick rolling). According to the analysis of the results, 26 of the inter-item correlations were strong (.50-.66), 25 moderate (.31-.49) and 15 modest (.19-.29). Furthermore, latent variable modeling revealed a first order model with one general factor and an excellent fit between model and data (χ² = 62.542, DF = 54; RMSEA = .03, CI90 .00–.05; CFI = .99; SRMR = .03). Ranging between .38 and .80, the loading of the 12 items on the general factor were all significant. Our findings suggest that a general factor, conceptualized as a generic ball ability, underlie participants´ performances on the ball tasks. Due to the popularity of ball games and the usability of ball tasks in various assessment tools, evidence supporting the generality of a ball ability are expected to be further tested as well as inform interventions and valid measurements.
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| 10. |
- Rylander, Pär, 1973, et al.
(författare)
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The specificity versus generality of ball-handling skills – Empirical evidence for a general ball-handling ability
- 2019
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Ingår i: Human Movement Science. - : Elsevier BV. - 1872-7646 .- 0167-9457. ; 66, s. 477-486
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Tidskriftsartikel (refereegranskat)abstract
- The purpose of this study was to investigate if ball-handling skills are specific and uncorrelated (i.e., motor specificity), or if they share an underlying ball-handling ability (i.e., motor generality). To empirically investigate this question, we had a sample of 201 adolescents perform 12 novel ball-handling tasks. Using confirmatory factor analysis, we showed that a model based on the assumptions of the generality perspective was superior to a model based on assumptions of specificity. The general ball-handling factor did significantly influence the performance on all 12 tasks, with factor loadings ranging between 0.39 and 0.79. The results and it's practical implications are discussed in relation to development of sport specific skills.
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