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- Brodersen, Jakob, et al.
(författare)
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Condition-dependent individual decision-making determines cyprinid partial migration
- 2008
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Ingår i: Ecology. - : Wiley. - 0012-9658 .- 1939-9170. ; 89:5, s. 1195-1200
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Tidskriftsartikel (refereegranskat)abstract
- Partial migration is a common phenomenon among many animals and occurs in many types of ecosystems. Understanding the mechanisms behind partial migration is of major importance for the understanding of population dynamics and, eventually, ecosystem processes. We studied the effects of food availability on the seasonal partial migration of cyprinid fish from a lake to connected streams during winter by the use of passive telemetry. Fish with increased access to food were found to migrate in higher proportion, earlier in the season, and to reside in the streams for a longer period compared to fish with decreased access to food. Furthermore, fewer unfed migrants returned to the lake, indicating higher overwinter mortality. Our results suggest that individual fish trade off safety from predation and access to food differently depending on their body condition, which results in a condition-dependent partial migration. Hence, our main conclusion is that individual decision-making is based on assessment of own condition which offers a mechanistic explanation to partial migration. Moreover, this may be of high importance for understanding population responses to environmental variation as well as ecosystem dynamics and stability. Read More: http://www.esajournals.org/doi/abs/10.1890/07-1318.1
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| 2. |
- Brodersen, Jakob, et al.
(författare)
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Ecosystem effects of partial fish migration in lakes
- 2008
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Ingår i: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 117:1, s. 40-46
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Tidskriftsartikel (refereegranskat)abstract
- Migration is a widespread phenomenon in many ecosystems. Most often, studies on migration have focused on how migration strategies are dependent on ecological parameters, but little attention has been paid to the top-down effect of migration on ecosystem processes. Cyprinid fish in many European lakes undergo partial migration, where a part of the population leaves the lake and enters streams for the winter. In this study, we model the effect of partial migration by fish on lower trophic levels in a lake ecosystem. Our results suggest that spring phyto- and zooplankton dynamics, including occurrences of clear-water phases, can be related to the timing and magnitude of partial migration of planktivorous fish. From our results we conclude that partial migration can influence the dynamics of lower trophic levels in the ecosystem. Furthermore, we hypothesize that partial migration may affect the stability of alternative stable states and transitions between them.
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| 3. |
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| 4. |
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| 5. |
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| 6. |
- Brodersen, Jakob, et al.
(författare)
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Optimal Swimming Speed in Head Currents and Effects on Distance Movement of Winter-Migrating Fish.
- 2008
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Ingår i: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 3:5
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Tidskriftsartikel (refereegranskat)abstract
- Migration is a commonly described phenomenon in nature that is often caused by spatial and temporal differences in habitat quality. However, as migration requires energy, the timing of migration may depend not only on differences in habitat quality, but also on temporal variation in migration costs. Such variation can, for instance, arise from changes in wind or current velocity for migrating birds and fish, respectively. Whereas behavioural responses of birds to such changing environmental conditions have been relatively well described, this is not the case for fish, although fish migrations are both ecologically and economically important. We here use passive and active telemetry to study how winter migrating roach regulate swimming speed and distance travelled per day in response to variations in head current velocity. Furthermore, we provide theoretical predictions on optimal swimming speeds in head currents and relate these to our empirical results. We show that fish migrate farther on days with low current velocity, but travel at a greater ground speed on days with high current velocity. The latter result agrees with our predictions on optimal swimming speed in head currents, but disagrees with previously reported predictions suggesting that fish ground speed should not change with head current velocity. We suggest that this difference is due to different assumptions on fish swimming energetics. We conclude that fish are able to adjust both swimming speed and timing of swimming activity during migration to changes in head current velocity in order to minimize energy use.
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| 7. |
- Brodersen, Jakob
(författare)
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Seasonal partial migration of cyprinids - Causes and consequences
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Partial migration is a common phenomenon in animals but has mostly been studied in birds. However, partial migration of cyprinid fish from lakes into streams during winter is a wide-spread phenomenon. Despite the potential trophic effects from an absence of dominant planktivores from the lake during large parts of the winter, only few studies have described this phenomenon. This thesis considers various aspects of the seasonal migration of cyprinids. The major aim of the thesis is to explain when, how and why the fish migrates and what possible effects the migration has on the lake ecosystem. I have, together with my co-workers, found that the winter migration differs between different species of cyprinids and that only very few of the predatory fish follow their prey into the streams. The timing of the migration coincides with a drastic increase in the ratio between the predation risk and the potential growth rate for the cyprinids. This also provides a mechanistic explanation for the migration: fish migrate to decrease their mortality risk during winter when potential growth rate is low, since predation risk is lower in the streams than in the lakes, despite lower food abundance in the streams. However, as only a fraction of the population migrates, it is obviously not beneficial for all individuals to migrate. I have, by experimentally feeding fish in the lake prior to migration, found that well fed fish in high condition migrate more than poorly fed fish in low condition. This difference is likely caused by low amount of energy reserves in poorly fed fish, which would not last for a long stay in the streams, where food abundance is low. Instead, these low condition fish accept the higher predation risk in the lake where food abundance is higher. Lastly, I have through mathematical modeling showed that the absence of fish from the lake during winter may have major effects on the lower trophic levels in the lake, especially during spring. For example, spring clear-water phases are more likely to occur when a high percentage of the fish population is migrating and when they stay away for a long time. This may be important for the establishment of macrophytes in lakes and may thus affect the stability and transitions between alternative stable states in lakes.
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| 8. |
- Brodersen, Jakob, et al.
(författare)
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Short-and long term niche segregation and individual specialization of brown trout (Salmo trutta) in species poor Faroese lakes
- 2012
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Ingår i: Environmental Biology of Fishes. - : Springer Science and Business Media LLC. - 0378-1909 .- 1573-5133. ; 93:3, s. 305-318
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Tidskriftsartikel (refereegranskat)abstract
- Trophic niche divergence is considered to be a major process by which species coexistence is facilitated. When studying niche segregation in lake ecosystems, we tend to view the niche on a one-dimensional pelagic-littoral axis. In reality, however, the niche use may be more complex and individual fidelity to a niche may be variable both between and within populations. In order to study this complexity, relative simple systems with few species are needed. In this paper, we study how competitor presence affects the resource use of brown trout (Salmo trutta) in 11 species-poor Faroese lakes by comparing relative abundance, stable isotope ratios and diet in multiple habitats. In the presence of three-spined sticklebacks (Gasterosteus aculeatus), a higher proportion of the trout population was found in the pelagic habitat, and trout in general relied on a more pelagic diet base as compared to trout living in allopatry or in sympatry with Arctic charr (Salvelinus alpinus). Diet analyses revealed, however, that niche-segregation may be more complex than described on a one-dimensional pelagic-littoral axis. Trout from both littoral and offshore benthic habitats had in the presence of sticklebacks a less benthic diet as compared to trout living in allopatry or in sympatry with charr. Furthermore, we found individual habitat specialization between littoral/benthic and pelagic trout in deep lakes. Hence, our findings indicate that for trout populations interspecific competition can drive shifts in both habitat and niche use, but at the same time they illustrate the complexity of the ecological niche in freshwater ecosystems.
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| 10. |
- Brodersen, Jakob, et al.
(författare)
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Variable individual consistency in timing and destination of winter migrating fish
- 2012
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Ingår i: Biology Letters. - : The Royal Society. - 1744-9561 .- 1744-957X. ; 8, s. 21-23
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Tidskriftsartikel (refereegranskat)abstract
- Migration is an important event in the life history of many animals, but there is considerable variation within populations in the timing and final destination. Such differential migration at the population level can be strongly determined by individuals showing different consistencies in migratory traits. By tagging individual cyprinid fish with uniquely coded electronic tags, and recording their winter migrations from lakes to streams for 6 consecutive years, we obtained highly detailed long-term information on the differential migration patterns of individuals. We found that individual migrants showed consistent site fidelities for over-wintering streams over multiple migratory seasons and that they were also consistent in their seasonal timing of migration. Our data also suggest that consistency itself can be considered as an individual trait, with migrants that exhibit consistent site fidelity also showing consistency in migratory timing. The finding of a mixture of both consistent and inconsistent individuals within a population furthers our understanding of intrapopulation variability in migration strategies, and we hypothesize that environmental variation can maintain such different strategies.
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