| 11. |
- Persson, Anders, et al.
(författare)
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Trophic interactions
- 2018
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Ingår i: Biology and ecology of pike. - Boca Raton : CRC Press. - 9781482262902
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Bokkapitel (refereegranskat)
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| 12. |
- Ahlberg, Erik, et al.
(författare)
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"Vi klimatforskare stödjer Greta och skolungdomarna"
- 2019
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Ingår i: Dagens nyheter (DN debatt). - 1101-2447.
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Tidskriftsartikel (populärvet., debatt m.m.)abstract
- DN DEBATT 15/3. Sedan industrialiseringens början har vi använt omkring fyra femtedelar av den mängd fossilt kol som får förbrännas för att vi ska klara Parisavtalet. Vi har bara en femtedel kvar och det är bråttom att kraftigt reducera utsläppen. Det har Greta Thunberg och de strejkande ungdomarna förstått. Därför stödjer vi deras krav, skriver 270 klimatforskare.
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| 13. |
- Persson, Anders, et al.
(författare)
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Foraging capacities and effects of competitive release on ontogenetic diet shift in bream, Abramis brama
- 2002
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Ingår i: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 97:2, s. 271-281
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Tidskriftsartikel (refereegranskat)abstract
- Bream Abramis brama) undergo ontogenetic diet shift from zooplankton to benthic macroinvertebrates, but the switching size may be highly variable. To unravel under what conditions bream are pelagic versus benthic foragers, we experimentally determined size-dependent foraging capacities on three prey types from the planktivory and benthivory niche: zooplankton, visible and buried macroinvertebrates. From these data we derived predictions of size-dependent diet preferences from estimates of prey value and competitive ability, and tested these predictions on diet data from the field. Planktivorous foraging capacity described a hump-shaped relationship with bream length that peaked for small bream of 67 mm total length. Benthivory capacity increased with increasing bream size, irrespective if benthic prey were visible on the sediment surface or buried in the sediment. From the experimental data and relationships of metabolic demand we calculated minimum resource requirement for maintenance (MRR) for each of the prey categories used in experiments. MRR increased with bream size for both zooplankton and visible chironomids, but decreased with bream size for buried chironomids, suggesting that intermediate sized bream (120-300 mm) may be competitively sandwiched between small and large bream that are more competitive planktivores and benthivores, respectively. Prey value estimates and competitive abilities qualitatively predicted diet shift in a bream population being released from competition. Competitive release did not change the diet of the largest size-class feeding on an optimal diet of benthic invertebrates both before and after competitive release. However, profound diet shifts towards benthic macro invertebrates were recorded for intermediate size-classes that fed on a suboptimal diet prior to competitive release. Thus, laboratory estimates of size-dependent foraging capacity of bream in planktivorous and benthivorous feeding niches provided useful information on size-specific competitive ability, and successfully predicted diet preference in the field.
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| 14. |
- Persson, Anders, et al.
(författare)
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Foraging capacity and resource synchronization in an ontogenetic diet switcher, pikeperch (Stizostedion lucioperca)
- 2002
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Ingår i: Ecology. - 0012-9658. ; 83:11, s. 3014-3022
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Tidskriftsartikel (refereegranskat)abstract
- Species undergoing ontogenetic diet shifts face a risk of resource competition that delays transitions between feeding stages. Such ontogenetic bottlenecks are common in piscivorous fish because competition with future prey may retard growth and prevent a size advantage. In pikeperch (Stizostedion lucioperca), year class strength of 0+ cohorts is highly variable and positively related to early onset of piscivory. To identify the causes of this pattern, we experimentally quantified size-dependent planktivorous and piscivorous foraging capacity and incorporated the data into a growth model. For any given prey type and size, foraging capacity described a hump-shaped relationship with predator size. Foraging capacity on daphnids peaked at a pikeperch length of 66 mm, suggesting a narrow scope of planktivory. The highest capacity in the piscivorous niche was reached at a predator-to-prey length ratio of 5, where the ratio was an integrated measure of predator size over several prey sizes. With the growth model, we derived size distributions of 0+ cohorts as functions of resource levels. Simulations revealed two major determinants for the year class strength of pikeperch. First, discontinuous availability of prey sizes counteracted switching to piscivory within the first growing season. This was accentuated by prey fish growth, which caused the planktivory and piscivory niches to separate over time and limited the time window when diet shift was possible. Second, the hump-shaped relationship between size and foraging capacity resulted in growth reduction when growing out of the planktivorous niche. Switching to piscivory in our model occurred along a perpendicular relationship between fish prey and zooplankton density. Zooplankton density determined whether pikeperch reached a size advantage over prey, and fish prey density affected whether the foraging return of piscivory was higher than planktivory. Individuals not reaching a size advantage over prey and failing to become piscivorous were stunted at a size when consumption balanced metabolic requirements. Piscivorous individuals, however, continued to grow fast throughout the season by feeding on the wave of the prey cohort. Our results highlight the importance for predators that shift diet to be synchronized with fluctuations in resource availability, such as the pulses of new cohorts of prey fish.
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| 15. |
- Persson, Anders, et al.
(författare)
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Pikeperch Sander lucioperca trapped between niches: foraging performance and prey selection in a piscivore on a planktivore diet
- 2008
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Ingår i: Journal of Fish Biology. - : Wiley. - 0022-1112 .- 1095-8649. ; 73:4, s. 793-808
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Tidskriftsartikel (refereegranskat)abstract
- The foraging behaviour of planktivorous pikeperch Sander lucioperca during their first growing season was analysed. Field data showed that S. lucioperca feed on extremely rare prey at the end of the summer, suggesting the presence of a bottleneck. In experiments, foraging ability of planktivorous S. lucioperca was determined when fish were feeding on different prey types (Daphnia magna or Chaoborus spp.) and sizes (1). magna of lengths I or 2.5 turn) when they Occurred alone. Front these results, the minimum density requirement of each prey type was analysed. The energy gain for three different foraging strategies was estimated; a specialized diet based on either large D. magna or Chaoborus spp. or I generalist diet combining both prey types. Prey value estimates showed that Chaoborus Spp. Should be the preferred prey, assuming an energy maximizing principle. In prey choice experiments, S. lucioperca largely followed this principle, including D. magna in the diet only when the density of the Chaoborus spp). was below a threshold value. Splitting the foraging bout into different sequences, however, resulted in a somewhat different pattern. During an initial phase, S. lucioperca captured both prey as encountered and then switched to Chaoborus spp. if prey density wits above (he threshold level. The prey selection observed was mainly explained by sampling behaviour and incomplete information about environmental quality, whereas satiation only had marginal effects. It was concluded that the observed diet based on rare prey items wits in accordance with an optimal foraging strategy and may generate positive growth in the absence of prey fish in suitable sizes. (c) 2008 The Authors Journal compilation (c) 2008 The Fisheries Society of the British Isles.
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| 16. |
- Ranåker, Lynn, et al.
(författare)
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Piscivore-Prey Fish Interactions : Mechanisms behind Diurnal Patterns in Prey Selectivity in Brown and Clear Water
- 2014
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Ingår i: PLOS ONE. - : Public Library of Science. - 1932-6203. ; 9:11, s. e102002-
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Tidskriftsartikel (refereegranskat)abstract
- Environmental change may affect predator-prey interactions in lakes through deterioration of visual conditions affecting foraging success of visually oriented predators. Environmental change in lakes includes an increase in humic matter causing browner water and reduced visibility, affecting the behavioural performance of both piscivores and prey. We studied diurnal patterns of prey selection in piscivorous pikeperch (Sander lucioperca) in both field and laboratory investigations. In the field we estimated prey selectivity and prey availability during day and night in a clear and a brown water lake. Further, prey selectivity during day and night conditions was studied in the laboratory where we manipulated optical conditions (humic matter content) of the water. Here, we also studied the behaviours of piscivores and prey, focusing on foraging-cycle stages such as number of interests and attacks by the pikeperch as well as the escape distance of the prey fish species. Analyses of gut contents from the field study showed that pikeperch selected perch (Perca fluviatilis) over roach (Rutilus rutilus) prey in both lakes during the day, but changed selectivity towards roach in both lakes at night. These results were corroborated in the selectivity experiments along a brown-water gradient in day and night light conditions. However, a change in selectivity from perch to roach was observed when the optical condition was heavily degraded, from either brown-stained water or light intensity. At longer visual ranges, roach initiated escape at distances greater than pikeperch attack distances, whereas perch stayed inactive making pikeperch approach and attack at the closest range possible. Roach anti-predatory behaviour decreased in deteriorated visual conditions, altering selectivity patterns. Our results highlight the importance of investigating both predator and prey responses to visibility conditions in order to understand the effects of degrading optical conditions on piscivore-prey interaction strength and thereby ecosystem responses to brownification of waters.
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| 17. |
- Turesson, Håkan, et al.
(författare)
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Prey size selection in piscivorous pikeperch (Stizostedion lucioperca) includes active prey choice
- 2002
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Ingår i: Ecology of Freshwater Fish. - : Wiley. - 0906-6691 .- 1600-0633. ; 11:4, s. 223-233
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Tidskriftsartikel (refereegranskat)abstract
- Knowledge of the mechanisms behind prey selection in piscivorous fish is important for our understanding of the dynamics of freshwater systems. Prey selection can involve active predator choice or be a passive process. We experimentally studied size-selectivity in pikeperch, feeding on roach and rudd. When given a choice of different prey sizes, pikeperch selected small prey. Passive selection mechanisms ( encounter rate, capture success and satiation) could not fully explain the pattern of diet choice. Instead, behavioural analysis revealed that the pikeperch actively selected small-sized prey. Optimal foraging theory, predicting that predators will choose prey sizes giving highest energy return per time spent foraging, is assumed to explain active choice. We measured handling times for a range of prey sizes and found that the most profitable sizes were also the chosen ones, both in experiments and in the field. This suggests that pikeperch choose their prey to maximise energy intake per unit time.
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