| 1. |
- Andersson, Jens, et al.
(author)
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Plastic reources polymorphism : effects or resource availability on Arctic char (Salvelinus alpinus) morphology
- 2005
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In: Biological Journal of the Linnean Society. - London : Acad. P.. - 0024-4066 .- 1095-8312. ; 85:3, s. 341-351
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Journal article (peer-reviewed)abstract
- Resource polymorphism has been suggested to be a platform for speciation. In some cases resource polymorphism depends on phenotypic plasticity but in other cases on genetic differences between morphotypes, which in turn has been suggested to be the ongoing development of a species pair. Here we study environmentally induced morphological differences in two age classes of Arctic char (Salvelinus alpinus) influencing char performance and diet in relation to resource availability. We found that structurally complex habitats with relatively lower zooplankton densities gave rise to individuals with a deeper body, and a downward positioned tip of the snout compared with individuals from structurally simple habitats with relatively higher zooplankton densities for both age classes. Environment also had an effect on foraging efficiency on zooplankton, with fish from structurally simple habitats had a higher foraging rate than fish from structurally complex habitats. Diet analyses showed that resource use in char mainly depends on the relative abundance of different resources. Therefore, to gain further understanding of resource polymorphism we suggest that future studies must include population dynamic feedbacks by the resources on the consumers.
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| 2. |
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| 3. |
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| 4. |
- Ask, Jenny, et al.
(author)
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Importance of coastal primary production in the northern Baltic Sea
- 2016
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In: Ambio. - : Springer Science and Business Media LLC. - 0044-7447 .- 1654-7209. ; 45:6, s. 635-648
-
Journal article (peer-reviewed)abstract
- In this study, we measured depth-dependent benthic microalgal primary production in a Bothnian Bay estuary to estimate the benthic contribution to total primary production. In addition, we compiled data on benthic microalgal primary production in the entire Baltic Sea. In the estuary, the benthic habitat contributed 17 % to the total annual primary production, and when upscaling our data to the entire Bothnian Bay, the corresponding value was 31 %. This estimated benthic share (31 %) is three times higher compared to past estimates of 10 %. The main reason for this discrepancy is the lack of data regarding benthic primary production in the northern Baltic Sea, but also that past studies overestimated the importance of pelagic primary production by not correcting for system-specific bathymetric variation. Our study thus highlights the importance of benthic communities for the northern Baltic Sea ecosystem in general and for future management strategies and ecosystem studies in particular.
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| 5. |
- Ask, Jenny, 1976-, et al.
(author)
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Terrestrial organic matter and light penetration : Effects on bacterial and primary production in lakes
- 2009
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In: Limnology and Oceanography. - : American Society of Limnology and Oceanography, Inc.. - 0024-3590 .- 1939-5590. ; 54:6, s. 2034-2040
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Journal article (peer-reviewed)abstract
- We investigated productivity at the basal trophic level in 15 unproductive lakes in a gradient ranging from clear-water to brown-water (humic) lakes in northern Sweden. Primary production and bacterial production in benthic and pelagic habitats were measured to estimate the variation in energy mobilization from external energy sources (primary production plus bacterial production on allochthonous organic carbon) along the gradient. Clear-water lakes were dominated by autotrophic energy mobilization in the benthic habitat, whereas humic lakes were dominated by heterotrophic energy mobilization in the pelagic habitat. Whole-lake (benthic + pelagic) energy mobilization was negatively correlated to the light-extinction coefficient, which was determined by colored terrestrial organic matter in the lake water. Thus, variation in the concentration of terrestrial organic matter and its light-absorbing characteristics exerts strong control on the magnitude, as well as on the processes and pathways, of energy mobilization in unproductive lakes. We suggest that unproductive lakes in general are sensitive to input of terrestrial organic matter because of its effects on basal energy mobilization in both benthic and pelagic habitats.
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| 6. |
- Ask, Jenny, 1976-, et al.
(author)
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Whole-lake estimates of carbon flux through algae and bacteria in benthic and pelagic habitats of clear-water lakes
- 2009
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In: Ecology. - Washington, DC, USA : Ecological Society of America. - 0012-9658 .- 1939-9170. ; 90:7, s. 1923-1932
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Journal article (peer-reviewed)abstract
- This study quantified new biomass production of algae and bacteria in both benthic and pelagic habitats of clear-water lakes to contrast how carbon from the atmosphere and terrestrial sources regulates whole-lake metabolism. We studied four small unproductive lakes in subarctic northern Sweden during one summer season. The production of new biomass in both benthic and pelagic habitats was calculated as the sum of autotrophic production by algae and heterotrophic production by bacteria using allochthonous organic carbon (OC). Whole-lake production of new biomass was dominated by the benthic habitat (86% +/- 4% [mean +/- SD]) and by primary production (77% +/- 9%). Still, heterotrophic bacteria fueled by allochthonous OC constituted a significant portion of the new biomass production in both benthic (19% +/- 11%) and pelagic habitats (51% +/- 24%). In addition, overall net production (primary production minus respiration) was close to zero in the benthic habitats but highly negative (-163 +/- 81 mg C.m(-2).d(-1)) in pelagic regions of all lakes. We conclude (1) that allochthonous OC supported a significant part of total production of new biomass in both pelagic and benthic habitats, (2) that benthic habitats dominated the whole-lake production of new biomass, and (3) that respiration and net CO2 production dominated the carbon flux of the pelagic habitats and biomass production dominated the benthic carbon flux. Taken together, these findings suggest that previous investigations have greatly underestimated the productivity of clear-water lakes when benthic autotrophic production and metabolism of allochthonous OC have not been measured.
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| 7. |
- Ask, Per, 1978-, et al.
(author)
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Competition mediated coexistence of invading intermediate consumer, ninespine stickleback, and a resident omnivorous top predator, Arctic char
-
Other publication (other academic/artistic)abstract
- Climate change results in changes in the geographical distribution of species. Species invasion success into a new area is dependent both on the dispersal ability of species as well as the strength and identity of biotic interactions between resident and invading species. Coexistence in intraguild predation (IGP) systems depends on the relative strength of predation and competition interactions which in turn are temperature dependent. We investigated the effects of introducing an intermediate consumer, ninespine stickleback (Pungitius pungitius), into allopatric populations of the omnivorous top predator Arctic char (Salvelinus alpinus). Introductions were performed in lakes with different climate regimes, two tundra lakes and two forest lakes that differed in average summer temperatures with 1.4 ± 0.5 ºC (average ± 1SD). We found that sticklebacks were able to invade and increase in density in both tundra and forest lakes. Sticklebacks had strong negative effects on resource densities which also was reflected in a decreased growth of small char. Increasing stickleback density had a positive effect on growth of large adults and on the maximum size of char. We conclude that stickleback presence is not limited by biological interactions in these systems but rather by dispersion ability. We suggest that the size dependency in the response of char to the invasion of sticklebacks is fundamental for the successful invasion of sticklebacks, and that size dependent interactions including cannibalism play important roles for coexistence in natural IGP-systems.
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| 8. |
- Ask, Per, 1978-, et al.
(author)
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Temperature mediated effects on top consumer populations in subarctic lakes
-
Other publication (other academic/artistic)abstract
- The effects of temperature on top consumer populations in subarctic lake communities were studied by contrasting two lake pairs in different climate regimes: one pair on the low alpine tundra and one pair in the subalpine birch forest. We measured zooplankton and macroinvertebrate biomasses over the season and estimated population density and size structure of the top consumer Arctic char (Salvelinus alpinus). Furthermore, we modelled char growth using literature data on temperature dependent search rate, handling time and metabolic demands. The forest lakes were warmer than the tundra lakes. Char in the forest lakes were larger and had a higher individual growth compared to char in the tundra lakes, while population density and biomasses of char were not different between the forest and the tundra lakes. There were no differences in macroinvertebrate and zooplankton resource levels available for char between lake pairs. Our modeling of char growth revealed that higher temperature increased growth of char at the observed resource densities, suggesting that the higher temperature in the forest lakes was primarily the cause of the higher growth of char in these lakes. We suggest that cannibalism in char may regulate char recruitment and thereby population density and biomass of char leading to effects of increasing temperature on consumer biomass and consumer individual growth different from what is expected in pure consumer-resource systems. Our results emphasize the importance of feedbacks within ecosystems when addressing effects of climate change and increasing temperature on lake communities.
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| 9. |
- Berglund, Åsa M. M., 1978-, et al.
(author)
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Effects on the food-web structure and bioaccumulation patterns of organic contaminants in a climate-altered Bothnian Sea mesocosms
- 2023
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In: Frontiers in Marine Science. - : Frontiers Media S.A.. - 2296-7745. ; 10
-
Journal article (peer-reviewed)abstract
- Climate change is expected to alter global temperature and precipitation patterns resulting in complex environmental impacts. The proposed higher precipitation in northern Scandinavia would increase runoff from land, hence increase the inflow of terrestrial dissolved organic matter (tDOM) in coastal regions. This could promote heterotrophic bacterial production and shift the food web structure, by favoring the microbial food web. The altered climate is also expected to affect transport and availability of organic micropollutants (MPs), with downstream effects on exposure and accumulation in biota. This study aimed to assess climate-induced changes in a Bothnian Sea food web structure as well as bioaccumulation patterns of MPs. We performed a mesocosms-study, focusing on aquatic food webs with fish as top predator. Alongside increased temperature, mesocosm treatments included tDOM and MP addition. The tDOM addition affected nutrient availability and boosted both phytoplankton and heterotrophic bacteria in our fairly shallow mesocosms. The increased tDOM further benefitted flagellates, ciliates and mesozooplankton, while the temperature increase and MP addition had minor effect on those organism groups. Temperature, on the other hand, had a negative impact on fish growth and survival, whereas tDOM and MP addition only had minor impact on fish. Moreover, there were indications that bioaccumulation of MPs in fish either increased with tDOM addition or decreased at higher temperatures. If there was an impact on bioaccumulation, moderately lipophilic MPs (log Kow 3.6 - 4.6) were generally affected by tDOM addition and more lipophilic MPs (log Kow 3.8 to 6.4) were generally affected by increased temperature. This study suggest that both increased temperatures and addition of tDOM likely will affect bioaccumulation patterns of MPs in shallow coastal regions, albeit with counteracting effects.
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| 10. |
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| 11. |
- Byström, Mikael, 1963-
(author)
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En broder, gäst och parasit : Uppfattningar och föreställningar om utlänningar, flyktingar och flyktingpolitik i svensk offentlig debatt 1942-1947
- 2006
-
Doctoral thesis (other academic/artistic)abstract
- Earlier studies have proposed that Swedish refugee policy started to change around 1942, when a restrictive refugee policy became more generous and humanitarian. From a quantitative point of view this statement is true: there were about ten thousand refugees in 1941, compared to almost two hundred thousand by the end of the war. However, this does not tell us whether the well-known discourses of Swedish inter-war anti-Semitism, nationalism and xenophobia underwent the same changes. The aim of this dissertation is to analyse the public debate concerning foreigners, refugees and refugee policy in 1942–1947.The dissertation puts forward the hypothesis of The Nordic prerogative. In brief, this prerogative meant that Sweden primarily held itself obliged to accept ethnical Northeners as refugees, and looked upon this obligation as more important than other considerations, such as the refugee’s ideological views, need of protection or humanitarian needs. Symptomatically, the groups which could not be entirely encompassed within the idea of a Nordic prerogative, particularly the Balts and the Danish Jews, were perceived as the most problematical refugee groups, both on a general level of the debates, and in specific issues.The idea of a Nordic prerogative did not derive from a sense of ethnical fraternity and humanitarian considerations alone, however. Several undertakings were also brought about by pragmatic considerations. Sweden sought goodwill, and reception of refugees was seen as one way of winning it.The dissertation also shows that the idea of a Nordic prerogative seems to become less important when the refugee comes closer to the everyday life of Sweden, where the Nordic refugees too were referred to as ”foreigners”, ”aliens” etc. As such, they had to put up with being spoken of in negatively loaded expressions, in the same way as other foreigners.
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| 12. |
- Byström, Mikael, et al.
(author)
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Invandringens historia : från "folkhemmet" till dagens Sverige
- 2017
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Book (other academic/artistic)abstract
- Med denna kunskapsöversikt, som sträcker sig från folkhemsbygget under 1930-talet fram till dags dato, vill Delmi bidra till att ge en överskådlig bild av migrationen och dess betydelse. Översikten baserar sig på ett rikt urval av befintlig forskning på olika områden och den behandlar tre större frågekomplex: Hur utformades invandrings- och invandrarpolitiken? Vilka bakomliggande föreställningar styrde debatter, media och beslutsfattare? Hur såg praktiken ut när det gäller mottagande, försörjning, bemötande och deltagande i samhälls- och arbetsliv?
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| 13. |
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| 14. |
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| 15. |
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| 16. |
- Byström, Pär, et al.
(author)
-
Declining coastal piscivore populations in the Baltic Sea : where and when do sticklebacks matter?
- 2015
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In: Ambio. - : Springer Science and Business Media LLC. - 0044-7447 .- 1654-7209. ; 44:Suppl 3, s. S462-S471
-
Journal article (peer-reviewed)abstract
- Intraguild predation interactions make fish communities prone to exhibit alternative stable states with either piscivore or prey fish dominance. In the Baltic Sea, local declines of coastal piscivores like perch (Perca fluviatilis) have been observed to coincide with high densities of sticklebacks (Gasterosteus aculeatus). Mechanisms behind this shift between piscivore and stickleback dominance were studied both experimentally and in field. Results showed that predation by sticklebacks has a strong negative effect on perch larvae survival, but this effect rapidly decreases with increasing perch size, likely due to gape limitations and digestion constraints in sticklebacks. Large spatial and temporal variations in patterns of stickleback migration into perch spawning sites were observed. Whether or not high density of sticklebacks will cause declines in coastal piscivore populations is suggested to depend on the availability of spawning sites in which sticklebacks do not migrate into or arrive late in the reproduction season of coastal piscivores.
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| 17. |
- Byström, Pär, et al.
(author)
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Ontogenetic constraints and diet shifts in Perch (Perca fluviatilis) : mechanisms and consequences for intra-cohort cannibalism
- 2012
-
In: Freshwater Biology. - : Wiley. - 0046-5070 .- 1365-2427. ; 57:4, s. 847-857
-
Journal article (peer-reviewed)abstract
- 1. In many populations, sufficient size variation to allow for cannibalism may develop not only among age cohorts but also within them. Here, we used data on resource dynamics, consumer body size distribution and gape size limitation to unravel mechanisms promoting cannibalism within cohorts of young-of-the-year (YOY) perch (Perca fluviatilis). 2. Perch are strongly gape limited when feeding on large zooplankton during early ontogeny. As a consequence, only initially large fish were able to shift to feeding on abundant large invertebrates, necessary to sustain fast growth. 3. We suggest that a combination of high initial size variation and exclusive access to resources for individuals with an initial size advantage is a prerequisite for the development of a size distribution sufficient for intra-cohort cannibalism to occur. 4. During the time when cannibalism was observed, growth of the largest individuals in YOY perch cohorts was faster than that of smaller individuals. However, the energy gain from cannibalism did not increase growth rate enough to reach a size necessary to feed on more abundant size classes of victims, and therefore, the effect of cannibalism on overall cohort density was minor. 5. In addition to a high energy gain from cannibalism allowing for fast growth, strong resource limitation and slow growth rates of small individuals (i.e. potential victims) are a prerequisite not only for the development of intra-cohort cannibalism but also for its persistence.
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| 18. |
- Byström, Pär, et al.
(author)
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Preference for cannibalism and ontogenetic constraints in competitive ability of piscivorous top predators
- 2013
-
In: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 8:7, s. e70404-
-
Journal article (peer-reviewed)abstract
- We experimentally show that the piscivorous top predator Arctic char (Salvelinus alpinus) have higher attack rates on cannibal prey compared to the interspecific prey species ninespine stickleback (Pungitius pungitius), and that sticklebacks are more efficient competitiors for zooplankton resources compared to juvenile char. We also conducted a literature survey that together with our experiments showed that piscivorous top consumers selected cannibal prey over interspecific prey in 9 out of 10 cases. Our literature survey also showed that specialist prey species are competitively superior compared to juvenile piscivorous species within the zooplankton niche. We discuss our results in relation to omnivory in fish communities and we suggest that the observed general preference for cannibal prey over interspecific prey in piscivores and the competitive advantage of prey species over juvenile piscivores may be major mechanisms for coexistence in fish communities.
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| 19. |
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| 20. |
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| 21. |
- Byström, Pär, et al.
(author)
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Substitution of top predators : effects of pike invasion in a subarctic lake
- 2007
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In: Freshwater Biology. - : John Wiley & Sons, Inc. - 0046-5070 .- 1365-2427. ; 52:7, s. 1271–1280-
-
Journal article (peer-reviewed)abstract
- 1. Invasions of top predators may have strong cascading effects in ecosystems affecting both prey species abundance and lower trophic levels. A recently discussed factor that may enhance species invasion is climate change and in this context, we studied the effects of an invasion of northern pike into a subarctic lake ecosystem formerly inhabited by the native top predator Arctic char and its prey fish, ninespined stickleback. 2. Our study demonstrated a strong change in fish community composition from a system with Arctic char as top predator and high densities of sticklebacks to a system with northern pike as top predator and very low densities of sticklebacks. A combination of both predation and competition from pike is the likely cause of the extinction of char. 3. The change in top predator species also cascaded down to primary consumers as both zooplankton and predator-sensitive macroinvertebrates increased in abundance. 4. Although the pike invasion coincided with increasing summer temperatures in the study area we have no conclusive evidence that the temperature increase is the causal mechanism behind the pike invasion. But still, our study provides possible effects of future pike invasions in mountain lakes related to climate change. We suggest that future pike invasions will have strong effects in lake ecosystems, both by replacing native top consumers and through cascading effects on lower trophic levels.
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| 22. |
- Byström, Pär, 1974-, et al.
(author)
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Warming decrease fish population densities and biomass
-
Other publication (other academic/artistic)abstract
- Temperature impact all biota and ecosystems through its direct effect on the vital rates of primary producers and consumers. Still, how these changes in rates translates through ecosystem feed backs to the population level of top consumers are poorly understood. Here, we studied effects of temperature increase (+ 3 ̊C during ice free season) on fish population dynamics in a replicated large scale pond ecosystem experiment over 3 years. Increased temperature had no significant effect on whole ecosystem gross primary production while top down effects of warming on intermediate consumers changed from negative to positive due to negative effects of warming on fish population abundance. Total fish density and biomass and abundance of both mature and old fish decreased with warming, while proportion of young fish increased, with warming. The effects of warming on fish population demographics were likely due to that temperature increased cohort competition and fish energy requirements relative to resource production. Our results suggest that global warming may increase competition, favor young individuals and overall decrease fish population densities and biomass.
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| 23. |
- Calboli, Federico C. F., et al.
(author)
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A test for within-lake niche differentiation in the nine-spined sticklebacks (Pungitius pungitius)
- 2016
-
In: Ecology and Evolution. - : Wiley. - 2045-7758. ; 6:14, s. 4753-4760
-
Journal article (peer-reviewed)abstract
- Specialization for the use of different resources can lead to ecological speciation. Accordingly, there are numerous examples of ecologically specialized pairs of fish species in postglacial lakes. Using a polymorphic panel of single nucleotide variants, we tested for genetic footprints of within-lake population stratification in nine-spined sticklebacks (Pungitius pungitius) collected from three habitats (viz. littoral, benthic, and pelagic) within a northern Swedish lake. Analyses of admixture, population structure, and relatedness all supported the conclusion that the fish from this lake form a single interbreeding unit.
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| 24. |
- Capo, Eric, et al.
(author)
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Droplet digital PCR applied to environmental DNA, a promising method to estimate fish population abundance from humic-rich aquatic ecosystems
- 2021
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In: Environmental DNA. - : John Wiley & Sons. - 2637-4943. ; 3:2, s. 343-352
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Journal article (peer-reviewed)abstract
- Measures of environmental DNA (eDNA) concentrations in water samples have the potential to be both a cost-efficient and a nondestructive method to estimate fish population abundance. However, the inherent temporal and spatial variability in abiotic and biotic conditions in aquatic systems have been suggested to be a major obstacle to determine relationships between fish eDNA concentrations and fish population abundance. Moreover, once water samples are collected, methodological biases are common, which introduces additional sources of variation to potential relationships between eDNA concentrations and fish population abundance. Here, we evaluate the performance of applying the droplet digital PCR (ddPCR) method to estimate fish population abundance in experimental enclosures. Using large-scale enclosure ecosystems that contain populations of nine-spined stickleback (Pungitius pungitius), we compared the concentrations of fish eDNA (COI mitochondrial region, 134 bp) obtained with the ddPCR method with high precision estimates of fish population abundance (i.e., number of individuals) and biomass. To evaluate the effects of contrasted concentrations of humic substances (potential PCR inhibitors) on the performance of ddPCR assays, we manipulated natural dissolved organic carbon (DOC) concentrations (range 4–11 mg/L) in the enclosures. Additionally, water temperature (+2°C) was manipulated in half of the enclosures. Results showed positive relationships between eDNA concentration and fish abundance and biomass estimates although unexplained variation remained. Still and importantly, fish eDNA estimates from high DOC enclosures were not lowered by potential inhibitory effects with our procedure. Finally, water temperature (although only 2°C difference) was neither detected as a significant factor influencing fish eDNA estimates. Altogether, our work highlights that ddPCR-based eDNA is a promising method for future quantification of fish population abundance in natural systems.
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| 25. |
- Capo, Eric, et al.
(author)
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Droplet digital PCR assays for the quantification of brown trout (Salmo trutta) and Arctic char (Salvelinus alpinus) from environmental DNA collected in the water of mountain lakes
- 2019
-
In: PLOS ONE. - : Public Library of Science. - 1932-6203. ; 14:12
-
Journal article (peer-reviewed)abstract
- Classical methods for estimating the abundance of fish populations are often both expensive, time-consuming and destructive. Analyses of the environmental DNA (eDNA) present in water samples could alleviate such constraints. Here, we developed protocols to detect and quantify brown trout (Salmo trutta) and Arctic char (Salvelinus alpinus) populations by applying the droplet digital PCR (ddPCR) method to eDNA molecules extracted from water samples collected in 28 Swedish mountain lakes. Overall, contemporary fish CPUE (catch per unit effort) estimates from standardized survey gill nettings were not correlated to eDNA concentrations for either of the species. In addition, the measured environmental variables (e.g. dissolved organic carbon concentrations, temperature, and pH) appear to not influence water eDNA concentrations of the studied fish species. Detection probabilities via eDNA analysis showed moderate success (less than 70% for both species) while the presence of eDNA from Arctic char (in six lakes) and brown trout (in one lake) was also indicated in lakes where the species were not detected with the gillnetting method. Such findings highlight the limits of one or both methods to reliably detect fish species presence in natural systems. Additional analysis showed that the filtration of water samples through 1.2 mu m glass fiber filters and 0.45 mu m mixed cellulose ester filters was more efficient in recovering DNA than using 0.22 mu m enclosed polyethersulfone filters, probably due to differential efficiencies of DNA extraction. Altogether, this work showed the potentials and limits of the approach for the detection and the quantification of fish abundance in natural systems while providing new insights in the application of the ddPCR method applied to environmental DNA.
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| 26. |
- Capo, Eric, et al.
(author)
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Effects of filtration methods and water volume on the quantification of brown trout (Salmo trutta) and Arctic char (Salvelinus alpinus) eDNA concentrations via droplet digital PCR
- 2020
-
In: Environmental DNA. - : John Wiley & Sons. - 2637-4943. ; 2:2, s. 152-160
-
Journal article (peer-reviewed)abstract
- The quantification of the abundance of aquatic organisms via the use of environmental DNA (eDNA) molecules present in water is potentially a useful tool for efficient and noninvasive population monitoring. However, questions remain about the reliability of molecular methods. Among the factors that can hamper the reliability of the eDNA quantification, we investigated the influence of five filtration methods (filter pore size, filter type) and filtered water volume (1 and 2 L) on the total eDNA and the fish eDNA concentrations of two species, brown trout (Salmo trutta) and Arctic char (Salvelinus alpinus) from tanks with known number of individuals and biomass. We applied a droplet digital PCR (ddPCR) approach to DNA extracted from water samples collected from two cultivation tanks (each of them containing one of the targeted species). Results showed that the quantification of fish eDNA concentrations of both species varies with filtration methods. More specifically, the 0.45-µm Sterivex enclosed filters were identified to recover the highest eDNA concentrations. Difficulties to filter 2 L water samples were present for small pore size filters (≤0.45 µm) and likely caused by filter clogging. To overcome issues related to filter clogging, common in studies aiming to quantify fish eDNA molecules from water samples, we recommend a procedure involving filtration of multiple 1 L water samples with 0.45-µm enclosed filters, to recover both high quality and high concentrations of eDNA from targeted species, and subsequent processing of independent DNA extracts with the ddPCR method.
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| 27. |
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| 28. |
- Degerman, Rickard, et al.
(author)
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Food web interactions determine energy transfer efficiency and top consumer responses to inputs of dissolved organic carbon
- 2018
-
In: Hydrobiologia. - : Springer Science and Business Media LLC. - 0018-8158 .- 1573-5117. ; 805:1, s. 131-146
-
Journal article (peer-reviewed)abstract
- Climate change projections indicate increased precipitation in northern Europe, leading to increased inflow of allochthonous organic matter to aquatic systems. The food web responses are poorly known, and may differ depending on the trophic structure. We performed an experimental mesocosm study where effects of labile dissolved organic carbon (DOC) on two different pelagic food webs were investigated, one having zooplankton as highest trophic level and the other with planktivorous fish as top consumer. In both food webs, DOC caused higher bacterial production and lower food web efficiency, i.e., energy transfer efficiency from the base to the top of the food web. However, the top-level response to DOC addition differed in the zooplankton and the fish systems. The zooplankton production increased due to efficient channeling of energy via both the bacteria land the phytoplankton pathway, while the fish production decreased due to channeling of energy mainly via the longer and less efficient bacterial pathway. We conclude that the added DOC either acted as a subsidy by increasing the production of the top trophic level (mesozooplankton), or as a sink causing decreased top consumer production (planktivorous fish).
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| 29. |
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| 30. |
- Hamdan, Mohammed, et al.
(author)
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An experimental test of climate change effects in northern lakes : Increasing allochthonous organic matter and warming alters autumn primary production
- 2021
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In: Freshwater Biology. - : John Wiley & Sons. - 0046-5070 .- 1365-2427. ; 66:5, s. 815-825
-
Journal article (peer-reviewed)abstract
- Climate changes are predicted to influence gross primary production (GPP) of lakes directly through warming and indirectly through increased loads of allochthonous coloured dissolved organic matter (cDOM) from surrounding landscapes. However, few studies have investigated this combined effect.Here we tested the effects of warming (elevated 3celcius) and cDOM input (three levels of humic river water addition) on GPP in autumn (2 months including open water and ice-covered periods) in experimental pond ecosystems.The cDOM input decreased whole-ecosystem GPP at natural temperature conditions mainly as a result of lower benthic GPP not fully counteracted by an increase in pelagic GPP, while warming increased whole-ecosystem GPP due to a positive response of mainly pelagic GPP at all levels of cDOM input.Warming delayed autumn ice cover formation by 2 weeks but did not affect light availability in the water column compared to ambient ice-covered treatments. Gross primary production during this period was still affected by warming and cDOM.The results stress the importance of accounting for multiple climate drivers and habitats when predicting lake GPP responses to climate change. We conclude that climate change may shift whole-ecosystem GPP through different responses of habitat-specific GPP to increasing cDOM inputs and warming.
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| 31. |
- Hamdan, Mohammed, 1978-, et al.
(author)
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Carbon dioxide limitation of benthic primary production in a boreal lake
- 2022
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In: Freshwater Biology. - : John Wiley & Sons. - 0046-5070 .- 1365-2427. ; 67:10, s. 1752-1760
-
Journal article (peer-reviewed)abstract
- Gross primary production (GPP) by benthic microalgae growing on soft sediments is an important contributor to lake productivity in many lakes world-wide. As benthic microalgae have access to nutrients in the sediment they have been regarded as primarily controlled by light, while the role of CO2 as a limiting factor for benthic GPP in lake ecosystems is largely unknown.In this study, we experimentally tested for CO2 limitation of benthic GPP by collecting littoral surface sediments, with associated benthic microalgae, from a typical boreal lake. Intact sediment cores were incubated at different depths (light conditions) after addition of dissolved inorganic (bicarbonate) or organic (DOC; glucose) carbon as direct and indirect sources of CO2, respectively.Benthic microalgal GPP was stimulated by both dissolved inorganic carbon and DOC additions at high, but not at low, light levels.This study shows that benthic microalgal GPP can be CO2-limited when light is not limiting and suggests that both direct (e.g., via groundwater inflow) and indirect (via mineralisation of DOC) CO2 supply can stimulate benthic GPP.
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| 32. |
- Hamdan, Mohammed, et al.
(author)
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Carbon dioxide stimulates lake primary production
- 2018
-
In: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 8
-
Journal article (peer-reviewed)abstract
- Gross primary production (GPP) is a fundamental ecosystem process that sequesters carbon dioxide (CO2) and forms the resource base for higher trophic levels. Still, the relative contribution of different controls on GPP at the whole-ecosystem scale is far from resolved. Here we show, by manipulating CO2 concentrations in large-scale experimental pond ecosystems, that CO2 availability is a key driver of whole-ecosystem GPP. This result suggests we need to reformulate past conceptual models describing controls of lake ecosystem productivity and include our findings when developing models used to predict future lake ecosystem responses to environmental change.
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| 33. |
- Hamdan, Mohammed, 1978-
(author)
-
Effects of temperature and terrestrial carbon on primary production in lake ecosystems
- 2021
-
Doctoral thesis (other academic/artistic)abstract
- Climate warming is predicted to affect northern lake food webs in two ways: (1)directly via changes in water temperature and ice conditions, and (2) indirectlyvia changes in catchment characteristics and processes that influence input ofallochthonous coloured dissolved organic matter (cDOM) and nutrients. Input ofcDOM increases carbon dioxide (CO2) availability, causes brownification andreduced light conditions, and may increase nutrient availability especially forpelagic primary producers. Increased water temperature and light penetrationand longer ice-free periods affect metabolic rates. These changes are expected toinfluence gross primary production (GPP) and growth of higher trophic levels.However, majority of studies focus on pelagic processes and net effects at wholelake scale is not well understood. Consequently, the lack of knowledge of whatfactors control benthic GPP makes predictions of net effects of climate change onwhole-ecosystem GPP spurious. The aim of this thesis was to experimentally testeffects of warming and increased input of allochthonous cDOM on habitatspecific and whole-ecosystem GPP in lakes. First, by manipulating the CO2concentrations in large scale pond ecosystems, we showed that increased CO2stimulated whole-ecosystem GPP. In a separate incubation study with naturallake sediments in a boreal lake, we tested the role of CO2 as a limiting factor forbenthic GPP under different light levels. The results showed that CO2 supplystimulated benthic GPP at high but not at low light availability, suggesting thatbenthic GPP can be CO2-limited. In the same experimental pond ecosystems, thecombined effect of increased allochthonous cDOM and warming (+3.5°C) on GPPwas studied. The results showed that cDOM input decreases whole-ecosystemGPP, mainly as a result of decreased benthic GPP due to light limitation not fullycounteracted by an increase in pelagic GPP under ambient conditions. Warmingon the other caused a hump shaped increase in whole-ecosystem GPP withincreasing cDOM input mainly due to a positive response in pelagic GPP due torelaxed nutrient limitation. Finally, by manipulating the fish consumer biomassin the same experimental pond ecosystems we showed that whole-ecosystem GPPcan be controlled by top-down effects under warm (+ 3.0°C) but not ambienttemperature conditions. The decline in whole-ecosystem GPP was mainlyattributed to a warming-stimulated consumer-driven trophic cascade in thepelagic habitat and top-down control by zooplankton on phytoplankton growth,while no corresponding cascade was evident in the benthic habitat.Taken together, the results suggest that climate change impacts, as increasinginputs of cDOM, warming and changes in food webs, have different effects onhabitat specific GPP and alone or in combination have impacts on whole-lakeGPP. This thesis offers important insights to better understand the factors thatcontrol lake GPP and to predict future lake ecosystem responses to environmentalchange.
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| 34. |
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| 35. |
- Hansen, Joakim, 1978-, et al.
(author)
-
Våtmarker som fiskevårdsåtgärd vid kusten : utvärdering av restaurerade våtmarkers effekt på fiskreproduktion och ekosystemet längs Östersjökusten
- 2020
-
Reports (other academic/artistic)abstract
- Många av Östersjöns kustfiskar är av sötvattenursprung och fortplantar sig i grunda vikar och kustnära våtmarker. Historiska utdikningar, kustexploatering och övergödning har lett till förluster av fiskens lek- och uppväxtområden, vilket tillsammans med fiske bidragit till minskande bestånd av exempelvis gädda och abborre. För att motverka nedgången har flera förvaltningsåtgärder initierats.Ungefär 100 våtmarker har restaurerats längs svenska ostkusten för att gynna reproduktionen av gädda och abborre. I samma syfte har fiskvandringshinder i kustmynnande vattendrag tagits bort på cirka 40 platser.Det fåtal uppföljningar som genomförts visar att sådana åtgärder har en god potential att bidra till stärkta kustbestånd av gädda och abborre. Mängden gäddyngel i kustvattnen utanför våtmarkerna tenderar att öka kraftigt efter åtgärderna, medan ingen tydlig förändring kan ses för mängden abborryngel. Det är dock stor variation i utfallet. En studie indikerar även en tydlig lokal ökning av gäddbestånden i kustvattnen utanför våtmarkerna. Sammanställningen visar även att borttagning av vandringshinder i kustmynnande vattendrag förbundna med olika sjösystem kan vara en effektivare metod än att restaurera våtmarker för attgynna abborre, vilket bör undersökas vidare.Det finns få studier som specifikt undersökt om åtgärderna kan ge så stark effekt på rovfiskbestånden att det indirekt påverkar resten av födoväven och ekosystemet. Det finns en potential för sådan påverkan. Men ökningen av rovfisk till följd av de åtgärdade våtmarkerna har i dagsläget inte varit tillräckligt kraftig för att leda till tydliga ekosystemeffekter, så som mindre mängd bytesfisk och påväxtalger.Även om våtmarker kan ge en lokal ökning av mängden fisk måste fler och kompletterande åtgärder till för att stärka kustens rovfiskbestånd. Åtgärderna bör utformas som en del av en tydligt samordnad och långsiktig förvaltning av kust och hav. Förutom en starkare reglering av kustfisket behövs exempelvis bättre skydd mot exploatering av fiskens lek- och uppväxtområden. Även lokal reduktion av mängden gråsäl och storskarv kan vara en möjlig åtgärd i områden där dessa rovdjur medför hög dödlighet på gädda och abborre.Utformningen av fiskeriförförvaltningen i öppet hav måste ha en mer rigid tillämpning av ekosystemansatsen och beakta konsekvenser för kustens ekosystem. Exempelvis tyder mycket på att förändringar i utsjöns fiskbestånd är en viktig bidragande orsak till att storspigg har ökat kraftigt de senaste decennierna. Storspiggen migrerar mellan utsjö och kust. Eftersom den äter gädd- och abborryngel minskar möjligheten att med lokala åtgärder stärka rovfiskbestånden vid kusten.Sammanställningen visar på en bristfällig koordinering och uppföljningav det senaste decenniets fiskevårdsåtgärder. För att skapa en bättre kunskapsbas för framtida förvaltningsbeslut finns därför ett behov av fler och samordnade mångåriga uppföljningar av åtgärder på såväl yngelproduktionoch lokala fiskbestånd som på kustekosystemet.
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| 36. |
- Hedström, Per, 1974-, et al.
(author)
-
Brownification increases winter mortality in fish
- 2017
-
In: Oecologia. - : Springer Science and Business Media LLC. - 0029-8549 .- 1432-1939. ; 183:2, s. 587-595
-
Journal article (peer-reviewed)abstract
- In northernclimateswinter is a bottleneck for many organisms. Low light and resource availability constrain individual foraging rates,potentially leading tostarvation and increasedmortality.Increasinginput of humic substances to aquatic ecosystems causesbrownification of water and hence a further decreaseof light availability,which may lead tofurther decreased foraging ratesand starvation mortality during winter.To test this hypothesis, we measured the effectsof experimentally increased humicwaterinput on consumption and survival of young-of-the-year (YOY) three-spined stickleback (Gasterosteus aculeatus) over winterin largeoutdoor enclosures. Population densitieswereestimated in autumn andthefollowing springand food availabilityand consumptionwere monitoredoverwinter. As hypothesized,mortality washigher underhumic(76%)as compared to ambientconditions (64%).Also, body condition and ingested prey biomass werelower under humic conditionseven thoughresource availability wasnotlower under humic conditions. Light conditions were significantly poorer under humic conditions. This suggeststhat increased mortality and decreased body condition and ingested prey biomasswasnot due to decreased resource availability but due todecreasedsearch efficiencyin this visual feeding consumer. Increased future brownification of aquatic systems may therefore negatively affect both recruitment and densities of fish.
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| 37. |
- Hedström, Per, 1974-
(author)
-
Climate change impacts on production and dynamics of fish populations
- 2016
-
Doctoral thesis (other academic/artistic)abstract
- Ongoing climate change is predicted to increase water temperatures and export of terrestrial dissolved matter (TDOM) to aquatic ecosystems influencing ecosystem productivity, food web dynamics and production of top consumers. Ecosystem productivity is mainly determined by the rates of primary production (GPP) in turn controlled by nutrients, light availability and temperature, while temperature alone affect vital rates like consumption and metabolic rates and maintenance requirements of consumers. Increased level of TDOM causes brownification of water which may cause light limitation in algae and decrease GPP and especially so in the benthic habitat. Temperature increase has a been suggested to increase metabolic rates of consumers to larger extent than the corresponding effect on GPP, which suggest reduced top consumer biomass and production with warming.The aim of this thesis was to experimentally study the effects of increased temperature and TDOM on habitat specific and whole ecosystem GPP and fish densities and production. In a replicated large-scale pond experiment encompassing natural food webs of lotic ecosystems I studied population level responses to warming and brownification in the three- spined stickleback (Gasterosteus aculeatus).Results showed overall that warming had no effect on whole ecosystem GPP, likely due to nutrient limitation, while TDOM input decreased benthic GPP but stimulated pelagic GPP. In fish, results first of all suggested that recruitment in sticklebacks over summer was negatively affected by warming as maintenance requirements in relation to GPP increased and thereby increased starvation mortality of young-of-the-year (YOY) sticklebacks. Secondly, brownification increased mortality over winter in YOY as the negative effect on light conditions likely decreased search efficiency and caused lower consumption rates and starvation over winter in sticklebacks. Third, seasonal production of YOY, older, and total stickleback production was negatively affected by warming, while increased TDOM caused decreased YOY and total fish production. The combined effect of the two was intermediate but still negative. Temperature effects on fish production were likely a result of increased energy requirements of fish in relation to resource production and intake rates whereas the negative effect of TDOM likely was a result of decreased benthic resource production. Finally, effects of warming over a three-year period caused total fish density and biomass and abundance of both mature and old fish to decrease, while proportion of young fish increased. The main cause behind the strong negative effects of warming on fish population biomass and changes in population demographic parameters were likely the temperature driven increased energy requirements relative to resource production and cohort competition.The results from this thesis suggest that predicted climate change impacts on lentic aquatic ecosystems will decrease future densities and biomass of fish and negatively affect fish production and especially so in systems dominated by benthic resource production.
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| 38. |
- Hedström, Per, 1974-, et al.
(author)
-
Population and size dependent responses in fish production to climate change
-
Other publication (other academic/artistic)abstract
- Climate change is predicted to increase water temperatures and export of terrestrial dissolved matter (TDOM) to aquatic ecosystems with concomitant effects on ecosystem productivity and production of consumers at the top of the food web. Here we study how increased level of TDOM and temperature alone or in combination affect benthic and pelagic primary production and biomass production of fish in replicated large scale outdoor pond experiment. We increased temperature (+3 ̊C) and TDOM concentrations (×2.5) using natural high TDOM water from a small creek and used naturally reproducing three-spine sticklebacks (Gasterosteus aculeatus) populations as model fish species. Gross primary production (GPP) was similar to ambient control conditions in all treatments although increased TDOM concentrations deceased benthic but stimulated pelagic GPP, presumably as a result of decreased light availability and increased nutrient availability, respectively. The production of young-of-the-year (YOY), older, and total fish population were negatively affected by warming, whereas increased TDOM caused decreased YOY and total fish production. Effect of temperature on fish production were likely a result of increased metabolic cost in relation to resource production and intake rates whereas the negative effect of TDOM on fish production was likely a result of decreasing benthic resource production. However, the combined effect on fish production of warming and TDOM was only intermediate compared to individual treatments. Our study suggest climate change will lead to decreased fish production and that the effect may be most pronounced in clear systems dominated by benthic GPP .
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| 39. |
- Hedström, Per, et al.
(author)
-
Warming but not increased terrestrial doc has negative effects on fish recruitment
-
Other publication (other academic/artistic)abstract
- Water temperature and export of terrestrial dissolved organic carbon (DOC) to recipient aquatic ecosystems have strong impacts on ecosystem productivity. Increased DOC concentration causing brownification of water is argued to reduce fish production by decreasing light availability for autotrophic production. On the other hand, higher temperatures have been shown to correlate positively with fish recruitment. This increase has been related to increased growth rates and survival of young-of-the-year (YOY) fish with warming. However, whether or not increased temperature results in higher growth depends on resource availability, suggesting a relationship between individual gain and recruitment mediated via the interplay between resource production and temperature. In a replicated, large scale experimental pond ecosystem, we tested the effects of increased temperature (+3oC) and terrestrial DOC concentrations (+4 mg/l) on recruitment (size, density and biomass) of three-spined sticklebacks over one growth season. Gross primary production (GPP) was similar between treatments, whereas zooplankton and benthic invertebrate biomass were negatively affected by increased temperature and if any higher at increased DOC levels. Increased temperature had no effect on individual size but negative effects on body condition and recruitment of YOY sticklebacks, while increased DOC concentration had no effect on recruitment. No positive effect of temperature increase on GPP and decreased resource levels in combination with higher metabolic costs, are suggested to increase starvation mortality and to be the main mechanism behind observed negative effects of warming on recruitment. Based on our results, we suggest that climate change may, counter intuitively, have negative effects on fish recruitment due to decreased carrying capacity of nursery habitats as a consequence of increased energy requirements in juvenile fish in relation to the net effects on resource production and ecosystem productivity.
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| 40. |
- Huss, Magnus, 1979-, et al.
(author)
-
Effects of ontogenetic scaling on resource exploitation and cohort size distributions
- 2010
-
In: Oikos. - : John Wiley & Sons, Inc.. - 0030-1299 .- 1600-0706. ; 119:2, s. 384-392
-
Journal article (peer-reviewed)abstract
- Variation in growth rates among individuals leading to the formation of broad size distributions is commonly observed in animal cohorts. Here we use laboratory derived size-scaling relationships to identify mechanisms driving changes in size distribution patterns within cohorts during early ontogeny. We introduced young-of-the-year perch (Perca fluviatilis) cohorts with different variation in body size distributions in pond enclosures. We kept the exploitative competitive environment constant by adjusting the number of introduced fish such that metabolic requirements were constant between different treatments. Based on modelling results we theoretically derived relative growth rates of differently sized fish when only taken exploitative competitive interactions into account. In agreement with predictions we found that initial variation in body size was negatively correlated with subsequent changes in body size variation in the pond experiment. Corresponding results were obtained in a field study covering 13 studied young-of-the-year perch cohorts in a small lake. Besides having a lower maximum growth capacity, initially large fish also suffered more from resource limitation in our experiment. The results suggest that exploitation competition is a major factor behind growth patterns in young fish cohorts, generally leading to size convergence. To explain the commonly observed pattern of size divergence in animal cohorts, including fish, we suggest that differential timing of diet shifts or mechanisms not related to exploitative interactions must be taken into account. For diet shifts to lead to size divergence we suggest that individuals with an initial size advantage need access to an exclusive prey which has a high growth potential. This, in turn, allows initially larger individuals to surf on a wave of growing prey while individuals only capable to feed on a depressed initial resource experience low growth rates.
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| 41. |
- Huss, Magnus, 1979-, et al.
(author)
-
Growing through predation windows: : effects on body size development in young fish
- 2010
-
In: Oikos. - : Wiley. - 0030-1299 .- 1600-0706. ; 119, s. 1796-1804
-
Journal article (peer-reviewed)abstract
- Th e degree to which growth in early life stages of animals is regulated via density-dependent feedbacks through preyresources is much debated. Here we have studied the infl uence of size- and density-dependent mechanisms as well as sizeselectivepredation pressure by cannibalistic perch Perca fl uviatilis on growth patterns of young-of-the-year (YOY) perchcovering several lakes and years. We found no infl uence of initial size or temperature on early body size development ofperch. In contrast, there was a negative relationship between reproductive output and the length of YOY perch at fi ve weeksof age. However, rather than an eff ect of density-dependent growth mediated via depressed resources the relationship wasdriven by positive size-selective cannibalism removing large individuals. Hence, given a positive correlation between thedensity of victims and predation pressure by cannibals, size-dependent interactions between cannibals and their victimsmay wrongly be interpreted as patterns of density-dependent growth in the victim cohort. Overall, our results support theview that density-dependent resource-limitation in early life stages is rare. Still, patterns of density-dependent growth mayemerge, but from variation in size-selective predation pressure rather than density as such. Th is illustrates the importanceof taking overall population demography and predatory interactions into account when studying growth patterns amongrecruiting individuals.
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| 42. |
- Huss, Magnus, 1979-, et al.
(author)
-
Influence of growth history on the accumulation of energy reserves and winter mortality on young fish
- 2008
-
In: Canadian Journal of Fisheries and Aquatic Sciences. - : EBSCO Host. - 0706-652X .- 1205-7533. ; 65:10, s. 2149-2156
-
Journal article (peer-reviewed)abstract
- In seasonal environments accumulated energy reserves are important to avoid starvation mortality during periods of low resource levels. Here we investigated patterns of energy accumulation and the importance of growth history for winter survival in young-of-the-year Eurasian perch (Perca fluviatilis). Under simulated winter conditions in aquaria’s we showed that high winter mortality most likely relate to the depletion of energy reserves in small perch. Correspondingly in a field study, using 4 lakes covering 3-6 lake years each, overwinter survival within cohorts was positively related to individual size. However, average size in autumn did not explain the variation in overwinter survival between cohorts. Instead we showed that seasonal growth history is an important factor. High growth rates late in season may increase cohort survival over winter irrespective of average size, related to a positive growth dependent increase in allocation to energy reserves when approaching winter. Mechanisms regulating within-season temporal dynamics of growth rates are therefore suggested to be important for overall cohort performance.
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| 43. |
- Huss, Magnus, 1979-
(author)
-
Ontogenetic scaling and the development of within-cohort size structure
- 2009
-
Doctoral thesis (other academic/artistic)abstract
- It is increasingly recognized that individuals of the same species differ from each other and influence and respond to their environment in unique ways. This thesis deals with size variation among individuals that not only are of the same species but also of similar age. Such variation may develop even when individuals are born in the same environment, i.e. within a cohort. I have studied the sources and consequences of variation within and among cohorts from egg through early ontogeny using young-of-the-year (YOY) perch (Perca fluviatilis) as study organism. In agreement with predictions based on model results only taking exploitative interactions among individuals into account, I found that the broader the initial size distributions were, the more did the degree of size variation among individuals decrease over time. Still, with initially small size variation among individuals, in several experiments also size divergence was observed. Furthermore, size variation among individuals increased more under high compared to at low densities. Increased size variation over time may be explained by size-dependent diet shifts allowing for initially larger individuals to make an early diet shift when the first resource becomes limiting. However, as size divergence also was observed in situations with only shared resources available, it can be concluded that diet shifts are not a prerequisite for size divergence in young animal cohorts. Hence, I also suggest that mechanisms not related to competition for limiting resources, such as genetic variation, stochasticity and behavioural traits must be taken into account, especially when initial size differences are small. The importance of considering size variation among individuals within cohorts was demonstrated in a study of winter mortality in YOY perch cohorts. A large individual size in autumn was shown to increase overwinter survival within cohorts. However, late summer growth rather than average body size reached in autumn explained variation in overwinter survival between cohorts. Higher accumulation to lipid reserves and accordingly lower mortality over winter was observed in years with high growth rates late in the season. In another study I showed that apparent patterns of density-dependent growth can emerge among larval fish, but rather than a result of density-dependent resource limitation this was due to variation in size-selective predation pressure. Individuals in the right end of the size distributions grew in to a high predation pressure from cannibalistic perch when cannibal density was high, coinciding with high larval perch densities. Finally, as substantial size variation among individuals can develop within cohorts, also intra-cohort cannibalism can occur. Using a physiologically structured population model it was shown that the development of size bimodality within cohorts as a result of intra-cohort cannibalism is critically dependent on long hatching periods, high victim densities and density-dependent feedbacks on shared resources.
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| 44. |
- Huss, Magnus, 1979-, et al.
(author)
-
Resource heterogeneity, diet shifts and intra-cohort competition : effects on size divergence in YOY fish
- 2008
-
In: Oecologia. - Berlin / Heidelberg : Springer. - 0029-8549 .- 1432-1939. ; 158:2, s. 249-257
-
Journal article (peer-reviewed)abstract
- Most organisms exhibit a substantial size variation among individuals due to individual differences in experienced biotic and abiotic environmental conditions and because individuals undergo growth and development during most of their life time. One important issue in this context is how size variation within cohorts may develop over time. Here we tested the hypothesis, in gape-limited animals such as fish, that size divergence among individuals within a cohort depends on the opportunity to undergo size-dependent diet shifts, by allowing initially larger individuals to make an early diet shift when the first resource becomes limiting. We used young-of-the-year perch (Perca fluviatilis) as our study organism. Competitive intensity and the opportunity to undergo a diet shift from zooplankton to macroinvertebrates affected both mean growth rates and the extent to which inter-individual variation in growth was manifested. As predicted, increased competition combined with the presence of both zooplankton and benthic macroinvertebrates increased the degree of size variation. However, size divergence was also observed among individuals when only the initial resource, zooplankton, was available. We argue that only non-exploitative interactions, such as dominance structures and social interactions could have caused this latter pattern, as exploitative competition is expected to lead to size convergence due to the superior competitive ability of smaller individuals. Our results suggest that diet shifts are not a prerequisite for size divergence in animal cohorts and that dominance and social interactions may have similar effects on size variation within cohorts. Finally, development of size variation is suggested to have strong implications for overall cohort performance.
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| 45. |
- Huss, Magnus, 1979-, et al.
(author)
-
The origin and development of individual size variation in early pelagic stages of fish
- 2007
-
In: Oecologia. - Berlin / Heidelberg : Springer. - 0029-8549 .- 1432-1939. ; 153:1, s. 57-67
-
Journal article (peer-reviewed)abstract
- Size variation among individuals born at the same time in a common environment (within cohorts) is a common phenomenon in natural populations. Still, the mechanisms behind the development of such variation and its consequences for population processes are far from clear. We experimentally investigated the development of early within-cohort size variation in larval perch (Perca fluviatilis). Specifically we tested the influence of initial variation, resulting from variation in egg strand size, and intraspecific density for the development of size variation. Variation in egg strand size translated into variation in initial larval size and time of hatching, which, in turn, had effects on growth and development. Perch from the smallest egg strands performed on average equally well independent of density, whereas larvae originating from larger egg strands performed less well under high densities. We related this difference in density dependence to size asymmetries in competitive abilities leading to higher growth rates of groups consisting of initially small individuals under high resource limitation. In contrast, within a single group of larvae, smaller individuals grew substantially slower under high densities whereas large individuals performed equally well independent of density. As a result, size variation among individuals within groups (i.e. originating from the same clutch) increased under high densities. This result may be explained by social interactions or differential timing of diet shifts and a depressed resource base for the initially smaller individuals. It is concluded that to fully appreciate the effects of density-dependent processes on individual size variation and size-dependent growth, consumer feedbacks on resources need to be considered.
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| 46. |
|
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| 47. |
- Jonsson, Micael, et al.
(author)
-
Climate change modifies the size structure of assemblages of emerging aquatic insects
- 2015
-
In: Freshwater Biology. - : Wiley-Blackwell. - 0046-5070 .- 1365-2427. ; 60:1, s. 78-88
-
Journal article (peer-reviewed)abstract
- Climate change is expected to not only raise water temperatures, but also to cause brownification of aquatic ecosystems via increased inputs of terrestrial dissolved organic matter. While efforts have been made to understand how increased temperature and brownification separately influence aquatic food webs, their interactive effects have been less investigated. Further, although climate change effects on aquatic ecosystems likely will propagate to terrestrial consumers via changes in aquatic insect emergence, this has rarely been studied. We investigated the effect of climate change on aquatic insect emergence, in a large-scale outdoor pond facility where 16 sections - each containing natural food webs including a fish top-consumer population - were subjected to warming (3 degrees C above ambient temperatures) and/or brownification (by adding naturally humic stream water). Aquatic insect emergence was measured biweekly over 18weeks. We found no effect of warming or brownification on total emergent insect dry mass. However, warming significantly reduced the number of emergent Chironomidae, while numbers of larger taxa, Trichoptera and Ephemeroptera, remained unchanged. On average, 57% and 58% fewer Chironomidae emerged from the warmed clear and humic pond sections, respectively. This substantial decrease in emergent Chironomidae resulted in a changed community structure and on average larger individuals emerging from warm sections as well as from humic sections under ambient conditions. There was also a weak influence of fish biomass on the size structure of emergent aquatic insects, with a positive relationship between individual insect size and total fish biomass, but effects of fish were clearly subordinate to those of warming. Climate change impacts on aquatic systems can have widespread consequences also for terrestrial systems, as aquatic insects are ubiquitous and their emergence represents an important resource flow from aquatic to terrestrial environments. While we found that neither warming nor brownification quantitatively changed total aquatic insect emergence biomass, the warming-induced decrease in number of emergent Chironomidae and the subsequent increase in average body size will likely impact terrestrial consumers relying on emergent aquatic insect as prey.
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| 48. |
- Karlsson, Jan, et al.
(author)
-
Light limitation of nutrient-poor lake ecosystems
- 2009
-
In: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 460, s. 506-509
-
Journal article (peer-reviewed)abstract
- Productivity denotes the rate of biomass synthesis in ecosystems and is a fundamental characteristic that frames ecosystem function and management. Limitation of productivity by nutrient availability is an established paradigm for lake ecosystems1, 2, 3. Here, we assess the relevance of this paradigm for a majority of the world's small, nutrient-poor lakes, with different concentrations of coloured organic matter4, 5. By comparing small unproductive lakes along a water colour gradient, we show that coloured terrestrial organic matter controls the key process for new biomass synthesis (the benthic primary production) through its effects on light attenuation. We also show that this translates into effects on production and biomass of higher trophic levels (benthic invertebrates and fish). These results are inconsistent with the idea that nutrient supply primarily controls lake productivity, and we propose that a large share of the world's unproductive lakes, within natural variations of organic carbon and nutrient input, are limited by light and not by nutrients. We anticipate that our result will have implications for understanding lake ecosystem function and responses to environmental change. Catchment export of coloured organic matter is sensitive to short-term natural variability and long-term, large-scale changes, driven by climate and different anthropogenic influences6, 7. Consequently, changes in terrestrial carbon cycling will have pronounced effects on most lake ecosystems by mediating changes in light climate and productivity of lakes.
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| 49. |
- Karlsson, Jan, et al.
(author)
-
Response to Comment: Terrestrial support of pelagic consumers in unproductive lakes : uncertainty and potential in assessments using stable isotopes
- 2014
-
In: Limnology and Oceanography. - : Wiley. - 1939-5590 .- 0024-3590. ; 59:5, s. 1800-1803
-
Journal article (peer-reviewed)abstract
- The use of stable carbon isotopes (d13C) has played a key role in estimation of the proportion of aquatic consumer biomass derived from terrestrial organic matter (OM; i.e., allochthony; Meili et al. 1996; Grey et al. 2001; Pace et al. 2004). However, the use of d13C for assessing allochthony has shortcomings because of the small natural separation between terrestrial and aquatic isotopic end members and the difficulty in physically separating autotrophic phytoplankton for d13C analysis from other components of particulate organic carbon (POC). These shortcomings are especially problematic in unproductive lakes where the phytoplankton are dominated by small and mixotrophic species, and where the internal photosynthesis is low compared to the input of terrestrial OM (Algesten et al. 2004; Jansson et al. 2008). Several alternative analyses and approaches have been tested to overcome these methodological limitations, including compound-specific analyses of phytoplankton biomarkers (Pace et al. 2007; Van Den Meersche et al. 2009; Berggren et al. 2014), manipulation of phytoplankton d13C by addition of 13C-labeled dissolved inorganic carbon (Pace et al. 2004; Taipale et al. 2008), addition of 13C-enriched OM (Karlsson et al. 2007; Bartels et al. 2012), and various mass balance and modeling approaches (Marty and Planas 2008; Mohamed and Taylor 2009; Berggren et al. 2010). Still, a generally applicable method is lacking, implying that the problems with assessing d13C of phytoplankton is a major limitation in the use of d13C for estimating allochthony with the accuracy needed for detailed understanding of food web dynamics.
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| 50. |
- Karlsson, Jan, et al.
(author)
-
Terrestrial organic matter input suppresses biomass production in lake ecosystems
- 2015
-
In: Ecology. - : Ecological Society of America. - 0012-9658 .- 1939-9170. ; 96:11, s. 2870-2876
-
Journal article (peer-reviewed)abstract
- Terrestrial ecosystems export large amounts of organic carbon (t-OC) but the net effect of this OC on the productivity of recipient aquatic ecosystems is largely unknown. In this study of boreal lakes, we show that the relative contribution of t-OC to individual top consumer (fish) biomass production, and to most of their potential prey organisms, increased with the concentration of dissolved organic carbon (DOC; dominated by t-OC sources) in water. However, the biomass and production of top consumers decreased with increasing concentration of DOC, despite their substantial use (up to 60%) of t-OC. Thus, the results suggest that although t-OC supports individual consumer growth in lakes to a large extent, t-OC input suppresses rather than subsidizes population biomass production.
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