| 1. |
- Berglund, Olof, et al.
(författare)
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Factors influencing organochlorine uptake in age-0 brown trout (Salmo trutta) in lotic environments
- 1997
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Ingår i: Canadian Journal of Fisheries and Aquatic Sciences. - 1205-7533. ; 54:12, s. 2767-2774
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Tidskriftsartikel (refereegranskat)abstract
- In 1994 and 1995, we investigated the relationship between stream morphology and water chemistry and levels of organochlorines (HCB, PCB, and DDT) in young-of-the-year brown trout (Salmo trutta) from 25 streams in southern Sweden. Contrary to earlier findings for lakes, we found a positive relationship between trophic status (total phosphorus) and uptake of persistent pollutants in stream biota (trout). This difference between benthic, stream environments and pelagic, lake environments may be related to processes affecting pollutant uptake, i.e., pollutant "spiralling" or the shift from heterotrophy to autotrophy in streams. Land use in the catchment area of the streams also affected pollutant levels in trout, with higher levels in agricultural landscapes and lower levels in forested areas. Size of catchment area, however, did not influence uptake of pollutants in trout. The results indicate that eutrophication of streams by agricultural activities and excessive nutrient loading may increase uptake of persistent pollutants in stream biota.
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| 2. |
- Brönmark, Christer, et al.
(författare)
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Decoupling of cascading trophic interactions in a freshwater, benthic food chain
- 1996
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Ingår i: Oecologia. - Heidelberg, Germany : Springer Berlin/Heidelberg. - 0029-8549 .- 1432-1939. ; 108:3, s. 534-541
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Tidskriftsartikel (refereegranskat)abstract
- Food chain theory provides explicit predictions for equilibrium biomasses among trophic levels in food chains of different lengths. Empirical studies on freshwater benthic food chains have typically been performed on chains with up to three levels and in field experiments with limited spatial and temporal scale. Here we use a ‘’natural snapshot experiment” approach to study equilibrium biomass and abundance among trophic levels in natural ponds differing only with respect to fish assemblage structure. Forty-four ponds were surveyed for their density and biomass of fish, snails and periphyton. Ponds were divided into three categories based on fish assemblage: ponds with no fish (two trophic levels), ponds with molluscivorous fish (three trophic levels), ponds with molluscivorous fish (three trophic levels) and ponds that also had piscivorous fish (four trophic levels). Ponds without fish had a high density and biomass of snails and a low biomass of periphyton, whereas snails with molluscivorous fish. In the presence of piscivores, molluscivore populations consisted of low numbers of large individuals. Snail assemblages in piscivore ponds were characterised by relatively high densities of small-bodied detritivorous species and periphyton biomass was not significantly different from ponds with three trophic levels. Thus, predictions from classic food chain theory were upheld in ponds with up to three trophic levels. In ponds with four trophic levels, however, there was a decoupling of the trophic cascade at the piscivore-molluscivore level. Gape-limited piscivory, predation on snails by molluscivores that have reached an absolute size refuge from predation, and changes in food preferences of the dominant snails are suggested to explain the observed patterns.
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| 3. |
- Brönmark, Christer, et al.
(författare)
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Predator-induced defense in crucian carp
- 1999
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Ingår i: The evolution of inducible defenses. - 0691012210 ; , s. 203-217
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 4. |
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| 5. |
- Hansson, Lars-Anders, et al.
(författare)
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Consumption patterns, complexity and enrichment in aquatic food chains
- 1998
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Ingår i: Royal Society of London. Proceedings B. Biological Sciences. - : The Royal Society. - 1471-2954. ; 265:1399, s. 901-906
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Tidskriftsartikel (refereegranskat)abstract
- The interactions between consumers and prey, and their impact on biomass distribution among trophic levels, are central issues in both empirical and theoretical ecology. In a long-term experiment, where all organisms, including the top predator, were allowed to respond to environmental conditions by reproduction, we tested predictions from `prey-dependent' and `ratio-dependent' models. Prey-dependent models made correct predictions only in the presence of strong interactors in simple food chains, but failed to predict patterns in more complex situations. Processes such as omnivory, consumer excretion, and unsuitable prey-size windows (invulnerable prey) increased the complexity and created patterns resembling ratio-dependent consumption. However, whereas the prey-dependent patterns were created by the mechanisms predicted by the model, ratio-dependent patterns were not, suggesting that they may be right for the wrong reason'. We show here that despite the enormous complexity of ecosystems, it is possible to identify and disentangle mechanisms responsible for observed patterns in community structure, as well as in biomass development of organisms ranging in size from bacteria to fish.
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| 6. |
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| 7. |
- Nilsson, Anders, et al.
(författare)
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Benefits of a predator induced morphology in crucian carp
- 1995
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Ingår i: Oecologia. - 1432-1939. ; 104:3, s. 291-296
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Tidskriftsartikel (refereegranskat)abstract
- Crucian carp (Carassius carassius) develop a deeper body in response to chemical cues from piscivores. This change in body morphology has been suggested to be a predator-induced defence. Here we investigate the possible benefits of the induced body morphology in laboratory experiments. Pike foraging behaviour when feeding on crucian carp of different body depths was recorded using video. Further, in a preference experiment pike were allowed to choose between shallow-bodied and deep-bodied crucian carp of similar lengths. Crucian carp body morphology did not affect predatory behaviours (activity, searching, following, observing, capture success) in northern pike, but an increase in crucian carp body depth led to an increase in handling time in pike. In the preference experiment, pike preferred shallow-bodied crucian carp over deep-bodied. Thus, a change in body morphology, induced by the presence of piscivores, benefits crucian carp by increasing piscivore handling times and an avoidance of the deep-bodied phenotype.
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| 8. |
- Nilsson, Anders, et al.
(författare)
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Foraging among cannibals and kleptoparasites: effects of prey size on pike behavior
- 1999
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Ingår i: Behavioral Ecology. - : Oxford University Press (OUP). - 1045-2249 .- 1465-7279. ; 10:5, s. 557-566
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Tidskriftsartikel (refereegranskat)abstract
- The northern pike (Esox lucius) is an important and selective piscivore that chooses smaller prey than predicted from energy / time budgets. In a laboratory experiment, we investigated pike predatory behavior to explain this selectivity. Northern pike feeding on different prey sizes in aquaria were observed when foraging alone, when in the presence of chemical cues from similar-sized or larger conspecifics, and when in the presence of conspecifics that were allowed to interact with the focal pike. The results show that prey handling time increases with prey size and that the duration of manipulating and handling prey inflicts a risk of exposure to cannibals and kleptoparasites on the pike. Therefore, the risk of falling victim to cannibals or kleptoparasites increases with prey size. Attracting and experiencing intraspecific interactors can be regarded as major fitness costs. Chemical cues from foraging conspecifics have only minor effects on pike foraging behavior. Furthermore, the ability to strike and swallow prey head first improves pike predatory performance because failing to do so increases handling time. Our findings emphasize the increasing potential costs with large prey and explain previous contradictory suggestions on the underlying mechanisms of behavior, selectivity, and trophic effects of northern pike predation.
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| 9. |
- Pettersson, Lars, et al.
(författare)
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Density-dependent costs of an inducible morphological defense in crucian carp
- 1997
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Ingår i: Ecology. - 0012-9658. ; 78:6, s. 1805-1815
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Tidskriftsartikel (refereegranskat)abstract
- ere should be fitness costs associated with the defense, otherwise it should be permanent. Thus, in the absence of predators and with limited resources, defended individuals are expected to be outcompeted by individuals lacking the costly defense. Crucian carp, Carassius carassius, increase in body depth in response to chemical stimuli from piscivorous fish, and the deeper body constitutes a morphological defense against gape-limited piscivores. Here, we have performed a field experiment investigating effects of population density on the relative competitive performance of shallow-bodied and deepbodied crucian carp. We assigned groups of six individually marked fish (the ‘‘focal’’ individuals) of either morph into enclosures with either low or high crucian carp density, and monitored changes in body mass, length, and body depth of these fish for 4 mo. In addition, we determined sex, and final liver and gonadal mass, of all focal fish. At high population density, there was a reduction in food resources (zooplankters), which resulted in reduced gonad mass, reduced gonadosomatic indices, and reduced growth in fish of both morphs. Unexpectedly, the relative allocation to livers was higher at high density. There was no difference in body mass gain between morphs at the low density, whereas at the high density shallow-bodied fish gained twice as much body mass as deepbodied fish. Hence, when predators were absent and food resources were limited, deepbodied individuals suffered a substantial cost when competing with shallow-bodied conspecifics. This study verifies the theoretical prediction that an inducible defense results in fitness costs in the absence of predators. Further, as we found no measurable disadvantage of the deep-bodied morphology at high food availability but a strong disadvantage under intense competition for food, our results also demonstrate the importance of relating defense costs to levels of intraspecific competition.
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| 10. |
- Pettersson, Lars, et al.
(författare)
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Energetic consequenses of an inducible morphological defence in crucian carp
- 1999
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Ingår i: Oecologia. - : Springer Science and Business Media LLC. - 1432-1939 .- 0029-8549. ; 121:1, s. 12-18
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Tidskriftsartikel (refereegranskat)abstract
- Crucian carp (Carassius carassius) increases in body depth in response to chemical cues from piscivores and the deeper body constitutes a morphological defence against gape-limited piscivores. In the ®eld, deep-bodied individuals su€er a density-dependent cost when com- peting with shallow-bodied conspeci®cs. Here, we use hydrodynamic theory and swimming respirometry to investigate the proposed mechanism underlying this ef- fect, high drag caused by the deep-bodied morphology. Our study con®rms that drag is higher for deep-bodied crucian carp, both in terms of estimated theoretical drag and power curve steepness. However, deep-bodied ®sh swimming at the velocity associated with minimum cost of transport, Umc, did not experience higher costs of transport than shallow-bodied ®sh. Deep-bodied crucian carp had signi®cantly lower standard metabolic rates, i.e. metabolic rates at rest, and also lower Umc, and the resulting costs of transport were similar for the two morphs. Nevertheless, when deep-bodied individuals deviate from Umc, e.g. when increasing foraging e€ort under competition, their steeper power curves will cause substantial energy costs relative to shallow-bodied con- speci®cs. Furthermore, there is evidence that reductions in standard metabolic rate incur costs in terms of lower stress tolerance, reduced growth rate, and life history changes. Thus, this work provides links between hy- drodynamics, a cost-reducing mechanism, and a density- dependent ®tness cost associated with an inducible defence.
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