| 1. |
- Jönsson, Mikael, et al.
(författare)
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Prey-type-dependent foraging of young-of-the-year fish in turbid and humic environments
- 2012
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Ingår i: Ecology of Freshwater Fish. - : Wiley. - 0906-6691 .- 1600-0633. ; 21:3, s. 461-468
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Tidskriftsartikel (refereegranskat)abstract
- Fish, which are generally visual foragers, experiences reduced reaction distance in visually degraded environments, which has consequences for encounter rates with prey. Small prey is detected at shorter distances than larger prey, and piscivores are therefore predicted to be more strongly affected by visual degradation. In experiments, roach (Rutilus rutilus) were fed two plankton prey types and pike (Esox lucius) were fed Daphnia and larval roach, in clear water, algal turbid water and water coloured brown by dissolved organic matter (DOM). Planktivorous foraging in roach was not affected by visual degradation, while pike foraging on both Daphnia and larval roach was. Pike showed increased reaction distance to Daphnia in visually degraded water, while it was severely reduced with roach as prey even if the visual range was not reduced below pike reaction distances in clear water. Pike foraging on Daphnia was not affected, but when foraging on roach, the reduced search efficiency was counteracted by increased attack rates. However, there was no increase in movement and no difference between turbid and DOM treatments. Effects on piscivores will likely become more pronounced at later life stages as prey size and the reliance on long-distance detection increases at the same time as changing climatic conditions may further deteriorate the visual conditions in future.
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| 2. |
- Ranåker, Lynn, et al.
(författare)
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Effects of brown and turbid water on piscivore-prey fish interactions along a visibility gradient
- 2012
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Ingår i: Freshwater Biology. - : Wiley. - 0046-5070 .- 1365-2427. ; 57, s. 1761-1768
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Tidskriftsartikel (refereegranskat)abstract
- 1. Environmental changes such as eutrophication and increasing inputs of humic matter (brownification) may have strong effects on predatorprey interactions in lakes through a reduction in the visual conditions affecting foraging behaviour of visually oriented predators. 2. In this experiment, we studied the effects of visual range (25200 cm) in combination with optically deteriorating treatments (algae, clay or brown humic water) on predatorprey interactions between pike (Esox lucius) and roach (Rutilus rutilus). We measured effects on reaction distance and strike distance for pike and escape distance for roach, when pike individuals were exposed to free-swimming roach as well as to roach held in a glass cylinder. 3. We found that reaction distance decreased with decreasing visual range caused by increasing levels of algae, clay or humic matter. The effect of reaction distance was stronger in turbid water (clay, algae) than in the brown water treatment. 4. Strike distance was neither affected by visual range nor by optical treatment, but we found shorter strike distances when pike attacked roach using visual cues only (roach held in a cylinder) compared to when pike could use multiple senses (free-swimming roach). Escape distance for roach was longer in turbid than in brown water treatments. 5. Changes in environmental drivers, such as eutrophication and brownification, affecting the optical climate should thus have consequences for the strength of predatorprey interactions through changes in piscivore foraging efficiency and prey escape behaviour. This in turn may affect lake ecosystems through higher-order interactions.
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| 3. |
- Ranåker, Lynn, et al.
(författare)
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Effects of degraded optical conditions on behavioural responses to alarm cues in a freshwater fish.
- 2012
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Ingår i: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 7:6
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Tidskriftsartikel (refereegranskat)abstract
- Prey organisms often use multiple sensory cues to gain reliable information about imminent predation threat. In this study we test if a freshwater fish increases the reliance on supplementary cues when the reliability of the primary cue is reduced. Fish commonly use vision to evaluate predation threat, but may also use chemical cues from predators or injured conspecifics. Environmental changes, such as increasing turbidity or water colour, may compromise the use of vision through changes in the optical properties of water. In an experiment we tested if changes in optical conditions have any effects on how crucian carp respond to chemical predator cues. In turbidity treatments we added either clay or algae, and in a brown water colour treatment we added water with a high humic content. We found that carp reduced activity in response to predator cues, but only in the turbidity treatments (clay, algae), whereas the response in the brown water treatment was intermediate, and not significantly different from, clear and turbid water treatments. The increased reliance on chemical cues indicates that crucian carp can compensate for the reduced information content from vision in waters where optical conditions are degraded. The lower effect in brown water may be due to the reduction in light intensity, changes in the spectral composition (reduction of UV light) or to a change in chemical properties of the cue in humic waters.
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| 4. |
- Ranåker, Lynn
(författare)
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Piscivore-prey fish interactions - consequences of changing optical environment
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Predator-prey interactions are a primary structuring force in aquatic systems. A change in the predator-prey interactions may cause a change in the strength of trophic cascades and even resulting in ecosystem shifts. However, individual properties of predators and prey, as well as environmental conditions, may affect the relative strength of predator-prey interactions. In our studies we observed two different behavioural defences against predators. Both crucian carp and perch decreased their activity when exposed to pike chemical or visual cue. However, the behavioural response elicited by the chemical cue was context dependent, i.e. crucian carp only reacted to the cue if information from visual senses was limited (turbid or brown water). Another behavioural response to predation threat is schooling as shown in roach, a common prey fish, that group into schools to limit predation risk. The interaction between the predator and prey fish was influenced by optical conditions. Reaction distance of pike showed to be negatively affected by reduced visual conditions. The reaction distance and attack distance of pike and escape distance of roach was also context dependent, where brown water increased the reaction and attack distance in pike and reduced the escape distance in roach. This resulted in an overlap in attack and escape distance, which may have positive effects on the capture success of pike. Pikeperch was less affected by changes of the visual conditions in the water. However, pikeperch was indirectly affected by changing optical conditions through a change in prey behaviour. Pikeperch showed a strong preference for perch under good optical conditions, but shifted their food preference to roach in poor optical conditions. The underlying mechanism to this pattern was observed in behavioural studies. Roach escaped long before the pikeperch initiated an attack, whereas perch was inactive which allowed pikeperch to approach and successfully attack. In poor optical conditions roach shoals were splitting up and roach escape distance was strongly reduced, which increased the foraging success of pikeperch resulting in that both roach and perch were included in the diet. These changes in the predator-prey interactions may explain some of the changes in fish growth rate observed in lakes along a gradient of brown colouration. Here, I found that the growth rate of pike and roach were reduced in browner lakes. Changes in environmental drivers, such as eutrophication and brownification, affecting the optical climate should thus have consequences for the strength of predator-prey interactions. This in turn may affect lake ecosystems through higher-order interactions.
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