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Scharnweber, Kristin
Publications (10 of 23) Show all publications
Marklund, M. H. K., Svanbäck, R., Zha, Y., Scharnweber, K. & Eklöv, P. (2018). The influence of habitat accessibility on the dietary and morphological specialisation of an aquatic predator. Oikos, 127(1), 160-169
Open this publication in new window or tab >>The influence of habitat accessibility on the dietary and morphological specialisation of an aquatic predator
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2018 (English)In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 127, no 1, p. 160-169Article in journal (Refereed) Published
Abstract [en]

Individual diet and habitat specialisation are widespread in animal taxa and often related to levels of predation and competition. Mobile consumers such as predatory fish can stabilise lake food webs by ranging over a larger area than their prey, thereby switching between habitats. Although, this switching assumes that the predator has equal preference for the available prey, individual diet specialisation and morphological adaptations to different habitats could potentially prevent individuals from switching between habitats. In this study, we assessed the niche width and individual specialisation in Eurasian perch Perca fluviatilis in response to a shift in habitat use by manipulating the ability for this top predator to couple habitats. We ran an eight weeks pond experiment, to test the effect of habitat switching on diet and morphological specialisations. We show that habitat coupling influenced individual diet specialisation and niche use in expected directions where specialisation increased with decreasing habitat switching. In contrast to expectations, the morphological variation decreased with increasing diet specialisation. Our results expand on previous work and suggest that individual specialisation and niche width can impact the ability of mobile predators to couple habitats. Furthermore, it shows the importance of individual specialisations in relation to habitat coupling.

Place, publisher, year, edition, pages
John Wiley & Sons, 2018
National Category
Ecology
Identifiers
urn:nbn:se:uu:diva-315718 (URN)10.1111/oik.04094 (DOI)000419102100015 ()
Funder
Swedish Research CouncilSwedish Research Council Formas
Available from: 2017-02-20 Created: 2017-02-20 Last updated: 2018-02-07Bibliographically approved
Lischke, B., Mehner, T., Hilt, S., Attermeyer, K., Brauns, M., Brothers, S., . . . Gaedke, U. (2017). Benthic carbon is inefficiently transferred in the food webs of two eutrophic shallow lakes. Freshwater Biology, 62(10), 1693-1706
Open this publication in new window or tab >>Benthic carbon is inefficiently transferred in the food webs of two eutrophic shallow lakes
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2017 (English)In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 62, no 10, p. 1693-1706Article in journal (Refereed) Published
Abstract [en]

1. The sum of benthic autotrophic and bacterial production often exceeds the sum of pelagic autotrophic and bacterial production, and hence may contribute sub- stantially to whole-lake carbon fluxes, especially in shallow lakes. Furthermore, both benthic and pelagic autotrophic and bacterial production are highly edible and of sufficient nutritional quality for animal consumers. We thus hypothesised that pelagic and benthic transfer efficiencies (ratios of production at adjacent trophic levels) in shallow lakes should be similar. 2. We performed whole ecosystem studies in two shallow lakes (3.5 ha, mean depth 2 m), one with and one without submerged macrophytes, and quantified pelagic and benthic biomass, production and transfer efficiencies for bacteria, phytoplank- ton, epipelon, epiphyton, macrophytes, zooplankton, macrozoobenthos and fish. We expected higher transfer efficiencies in the lake with macrophytes, because these provide shelter and food for macrozoobenthos and may thus enable a more efficient conversion of basal production to consumer production. 3. In both lakes, the majority of the whole-lake autotrophic and bacterial produc- tion was provided by benthic organisms, but whole-lake primary consumer pro- duction mostly relied on pelagic autotrophic and bacterial production. Consequently, transfer efficiency of benthic autotrophic and bacterial production to macrozoobenthos production was an order of magnitude lower than the transfer efficiency of pelagic autotrophic and bacterial production to rotifer and crustacean production. Between-lake differences in transfer efficiencies were minor. 4. We discuss several aspects potentially causing the unexpectedly low benthic transfer efficiencies, such as the food quality of producers, pelagic–benthic links, oxygen concentrations in the deeper lake areas and additional unaccounted con- sumer production by pelagic and benthic protozoa and meiobenthos at interme- diate or top trophic levels. None of these processes convincingly explain the large differences between benthic and pelagic transfer efficiencies. 5. Our data indicate that shallow eutrophic lakes, even with a major share of auto- trophic and bacterial production in the benthic zone, can function as pelagic sys- tems with respect to primary consumer production. We suggest that the benthic autotrophic production was mostly transferred to benthic bacterial production, which remained in the sediments, potentially cycling internally in a similar way to what has previously been described for the microbial loop in pelagic habitats. Understanding the energetics of whole-lake food webs, including the fate of the substantial benthic bacterial production, which is either mineralised at the sedi- ment surface or permanently buried, has important implications for regional and global carbon cycling

Keywords
bacterial production, benthic food chain, pelagic food chain, quantitative food webs, trophic transfer efficiency
National Category
Biological Sciences
Identifiers
urn:nbn:se:uu:diva-334883 (URN)10.1111/fwb.12979 (DOI)000410094000003 ()
Available from: 2017-11-29 Created: 2017-11-29 Last updated: 2018-05-17Bibliographically approved
Syväranta, J., Scharnweber, K., Brauns, M., Hilt, S. & Mehner, T. (2016). Assessing the utility of hydrogen, carbon and nitrogen stable isotopes in estimating consumer allochthony in two shallow eutrophic lakes. PLoS ONE, 11(5), Article ID e0155562.
Open this publication in new window or tab >>Assessing the utility of hydrogen, carbon and nitrogen stable isotopes in estimating consumer allochthony in two shallow eutrophic lakes
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2016 (English)In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 11, no 5, article id e0155562Article in journal (Refereed) Published
Abstract [en]

Hydrogen stable isotopes (δ2H) have recently been used to complement δ13C and δ15N in food web studies due to their potentially greater power to separate sources of organic matter in aquatic food webs. However, uncertainties remain regarding the use of δ2H, since little is known about the potential variation in the amount of exchangeable hydrogen (Hex) among common sample materials or the patterns of δ2H when entire food webs are considered. We assessed differences in Hex among the typical sample materials in freshwater studies and used δ2H, δ13C and δ15N to compare their effectiveness in tracing allochthonous matter in food webs of two small temperate lakes. Our results showed higher average amounts of Hex in animal tissues (27% in fish and macroinvertebrates, 19% in zooplankton) compared to most plant material (15% in terrestrial plants and 8% in seston/periphyton), with the exception of aquatic vascular plants (23%, referred to as macrophytes). The amount of Hex correlated strongly with sample lipid content (inferred from C:N ratios) in fish and zooplankton samples. Overall, the three isotopes provided good separation of sources (seston, periphyton, macrophytes and allochthonous organic matter), particularly the δ2H followed by δ13C. Aquatic macrophytes revealed unexpectedly high δ2H values, having more elevated δ2H values than terrestrial organic matter with direct implications for estimating consumer allochthony. Organic matter from macrophytes significantly contributed to the food webs in both lakes highlighting the need to include macrophytes as a potential source when using stable isotopes to estimate trophic structures and contributions from allochthonous sources.

National Category
Oceanography, Hydrology and Water Resources
Identifiers
urn:nbn:se:uu:diva-264655 (URN)10.1371/journal.pone.0155562 (DOI)000376587300006 ()27167517 (PubMedID)
Available from: 2015-10-15 Created: 2015-10-15 Last updated: 2018-01-11Bibliographically approved
Mikolajewski, D. J., Scharnweber, K., Jiang, B., Leicht, S., Mauersberger, R. & Johansson, F. (2016). Changing the habitat: the evolution of inter-correlated traits to escape from predators. Journal of Evolutionary Biology, 29(7), 1394-1405
Open this publication in new window or tab >>Changing the habitat: the evolution of inter-correlated traits to escape from predators
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2016 (English)In: Journal of Evolutionary Biology, ISSN 1010-061X, E-ISSN 1420-9101, Vol. 29, no 7, p. 1394-1405Article in journal (Refereed) Published
Abstract [en]

Burst escape speed is an effective and widely used behaviour for evading predators, with burst escape speed relying on several different morphological features. However, we know little about how behavioural and underlying morphological attributes change in concert as a response to changes in selective predation regime. We studied intercorrelated trait differentiation of body shape and burst-swim-mediating morphology in response to a habitat shift-related reduction in burst escape speed using larvae of the dragonfly genus Leucorrhinia. Species in this genus underwent a well-known habitat shift from predatory fish lakes (fish lakes) to predatory fish-free lakes dominated by large predatory dragonflies (dragonfly lakes) accompanied by relaxed selection on escape burst speed. Results revealed that species from fish lakes that possess faster burst speed have evolved a suite of functionally intercorrelated traits, expressing a wider abdomen, a higher abdominal muscles mass and a larger branchial chamber compared with species from dragonfly lakes. In contrast, populations within species did not show significant differences in muscle mass and branchial chamber size between lake types in three of the species. High multicollinearity among variables suggests that traits have evolved in concert rather than independently when Leucorrhinia shifted from fish lakes to dragonfly lakes. Thus, relaxed selection on burst escape speed in dragonfly-lake species resulted in a correlated reduction of abdominal muscles and a smaller branchial chamber, likely to save production and/or maintenance costs. Our results highlight the importance of studying integrated behavioural and morphological traits to fully understand the evolution of complex phenotypes.

National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-274555 (URN)10.1111/jeb.12879 (DOI)000382500100011 ()27062155 (PubMedID)
Available from: 2016-01-22 Created: 2016-01-22 Last updated: 2017-11-30Bibliographically approved
Scharnweber, K., Strandberg, U., Marklund, M. H. & Eklöv, P. (2016). Combining resource use assessment techniques reveals trade-offs in trophic specialization of polymorphic perch. Ecosphere, 7(8), Article ID e01387.
Open this publication in new window or tab >>Combining resource use assessment techniques reveals trade-offs in trophic specialization of polymorphic perch
2016 (English)In: Ecosphere, ISSN 2150-8925, E-ISSN 2150-8925, Vol. 7, no 8, article id e01387Article in journal (Refereed) Published
Abstract [en]

Trophic polymorphism has found to be common in many taxa and is a suggested mechanism of ecological speciation. To characterize the trophic linkages of specific morphotypes of organisms as well as a time-integrated niche use, several methods are available. In this study, we present data of multiple techniques to investigate the trophic divergence of Eurasian perch (Perca fluviatilis) that displays well-studied trophic polymorphism associated with littoral and pelagic habitats in lakes. We combined bulk stable isotope and fatty acid analyses on the muscle tissue of perch from three different lakes in Sweden with analyses of stomach content. By comparing the three methods, we aimed at providing a broad and highly resolved picture on the trophic divergence in freshwater fish. The degree in morphological divergence varied between perch caught in the three different lakes. Generally, perch caught in the pelagic zone were more streamlined compared to the ones caught in the littoral zone that had a deeper body, as shown by geometric morphometrics. The three diet assessment methods revealed different levels of information. Data on stomach content showed some preferences for specific dietary items in littoral and pelagic perch, but general trophic specialization could not be concluded due to the small sample size. Analyses of delta C-13 and delta N-15, however, confirmed these results as a long-term pattern connected to specific habitat use in two of the three lakes. Fatty acid signatures of perch reflected partly those of the prey items of the specific habitats. Although the proportions of the essential fatty acid 22:6n-3 were lower in littoral resources, the proportions in littoral fish were similar to the ones caught in the pelagic zone. We concluded that although a fundamental contribution from littoral resources exists in littoral phenotypes, a minor reliance on pelagic prey items is obviously needed to provide essential compounds. Thus, by combining the methods to characterize direct resource use (i.e., stomach analyses) with others that utilize trophic biomarkers (i.e., analyses of stable isotopes and fatty acids), we were able to illustrate the degree of variation in trophic divergence of perch but also shed some light on potential trade-offs that are related to resource specialization in freshwater fish.

Keywords
carbon stable isotopes; ecological speciation; fatty acid analysis; geometric morphometrics; Perca fluviatilis; resource polymorphism; Special Feature; Biomarkers in Trophic Ecology; stomach content analysis
National Category
Ecology
Identifiers
urn:nbn:se:uu:diva-264657 (URN)10.1002/ecs2.1387 (DOI)000387208900001 ()
Available from: 2015-10-15 Created: 2015-10-15 Last updated: 2017-12-01Bibliographically approved
Scharnweber, K., Strandberg, U., Karlsson, K. & Eklöv, P. (2016). Decrease of population divergence in Eurasian perch (Perca fluviatilis) in browning waters: role of fatty acids and foraging efficiency. PLoS ONE, 11(9), Article ID e0162470.
Open this publication in new window or tab >>Decrease of population divergence in Eurasian perch (Perca fluviatilis) in browning waters: role of fatty acids and foraging efficiency
2016 (English)In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 11, no 9, article id e0162470Article in journal (Refereed) Published
Abstract [en]

Due to altered biogeochemical processes related to climate change, highly colored dissolved organic carbon (DOC) from terrestrial sources will lead to a water "brownification" in many freshwater systems of the Northern Hemisphere. This will create deteriorated visual conditions that have been found to affect habitat-specific morphological variations in Eurasian perch (Perca fluviatilis) in a previous study. So far, potential drivers and ultimate causes of these findings have not been identified. We conducted a field study to investigate the connection between morphological divergence and polyunsaturated fatty acid (PUFA) composition of perch from six lakes across a gradient of DOC concentration. We expected a decrease in the prevalence of PUFAs, which are important for perch growth and divergence with increasing DOC concentrations, due to the restructuring effects of DOC on aquatic food webs. In general, rate of morphological divergence in perch decreased with increasing DOC concentrations. Proportions of specific PUFAs (22:6n-3, 18:3n-3, 20:5n-3, and 20:4n-6) identified to primarily contribute to overall differences between perch caught in clear and brown-water lakes tended to be connected to overall decline of morphological divergence. However, no overall significant relationship was found, indicating no severe limitation of essential fatty acids for perch inhabiting brown water lakes. We further broaden our approach by conducting a laboratory experiment on foraging efficiency of perch. Therefore, we induced pelagic and littoral phenotypes by differences in habitat-structure and feeding mode and recorded attack rate in a feeding experiment. Generally, fish were less efficient in foraging on littoral prey (Ephemeroptera) when visual conditions were degraded by brown water color. We concluded that browning water may have a strong effect on the forager's ability to find particular food resources, resulting in the reduced development of evolutionary traits, such as habitat-specific morphological divergence.

National Category
Oceanography, Hydrology and Water Resources Fish and Aquacultural Science
Identifiers
urn:nbn:se:uu:diva-302018 (URN)10.1371/journal.pone.0162470 (DOI)000383255900107 ()27610617 (PubMedID)
Funder
Swedish Research Council FormasSwedish Research CouncilGerman Research Foundation (DFG)
Available from: 2016-08-28 Created: 2016-08-28 Last updated: 2018-01-10Bibliographically approved
Lischke, B., Weithoff, G., Wickham, S., Attermeyer, K., Grossart, H.-P., Scharnweber, K., . . . Gaedke, U. (2016). Large biomass of small feeders: Ciliates may dominate herbivory in eutrophic lakes. Journal of Plankton Research, 38(1), 2-15
Open this publication in new window or tab >>Large biomass of small feeders: Ciliates may dominate herbivory in eutrophic lakes
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2016 (English)In: Journal of Plankton Research, ISSN 0142-7873, E-ISSN 1464-3774, Vol. 38, no 1, p. 2-15Article in journal (Refereed) Published
Abstract [en]

The importance of ciliates as herbivores and in biogeochemical cycles is increasingly recognized. An opportunity to observe the potential consequences of zooplankton dominated by ciliates arose when winter fish kills resulted in strong suppression of crustaceans by young planktivorous fish in two shallow lakes. On an annual average, ciliates made up 38-76% of the total zooplankton biomass in both lakes during two subsequent years. Consequently, ciliate biomass and their estimated grazing potential were extremely high compared with other lakes of various trophic states and depths. Grazing estimates based on abundance and size suggest that ciliates should have cleared the water column of small (<5 mu m) and intermediate (5-50 mu m) sized phytoplankton more than once a day. Especially, small feeders within the ciliates were important, likely exerting a strong top-down control on small phytoplankton. Particle-attached bacteria were presumably strongly suppressed by intermediate-sized ciliate feeders. In contrast to other lakes, large phytoplankton was proportionately very abundant. The phytoplankton community had a high evenness, which may be attributed to the feeding by numerous fast growing and selective ciliate species. Our study highlights ciliates as an important trophic link and adds to the growing awareness of the role of winter processes for plankton dynamics.

National Category
Natural Sciences Biological Sciences
Identifiers
urn:nbn:se:uu:diva-264654 (URN)10.1093/plankt/fbv102 (DOI)000371229900002 ()
Available from: 2015-10-15 Created: 2015-10-15 Last updated: 2017-12-01Bibliographically approved
Mehner, T., Attermeyer, K., Brauns, M., Brothers, S., Diekmann, J., Gaedke, U., . . . Hilt, S. (2016). Weak response of animal allochthony and production to enhanced supply of terrestrial leaf litter in nutrient-rich lakes. Ecosystems (New York. Print), 19(2), 311-325
Open this publication in new window or tab >>Weak response of animal allochthony and production to enhanced supply of terrestrial leaf litter in nutrient-rich lakes
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2016 (English)In: Ecosystems (New York. Print), ISSN 1432-9840, E-ISSN 1435-0629, Vol. 19, no 2, p. 311-325Article in journal (Refereed) Published
Abstract [en]

Ecosystems are generally linked via fluxes of nutrients and energy across their boundaries. For example, freshwater ecosystems in temperate regions may receive significant inputs of terrestrially derived carbon via autumnal leaf litter. This terrestrial particulate organic carbon (POC) is hypothesized to subsidize animal production in lakes, but direct evidence is still lacking. We divided two small eutrophic lakes each into two sections and added isotopically distinct maize litter to the treatment sections to simulate increased terrestrial POC inputs via leaf litter in autumn. We quantified the reliance of aquatic consumers on terrestrial resources (allochthony) in the year subsequent to POC additions by applying mixing models of stable isotopes. We also estimated lake-wide carbon (C) balances to calculate the C flow to the production of the major aquatic consumer groups: benthic macroinvertebrates, crustacean zooplankton, and fish. The sum of secondary production of crustaceans and benthic macroinvertebrates supported by terrestrial POC was higher in the treatment sections of both lakes. In contrast, total secondary and tertiary production (supported by both autochthonous and allochthonous C) was higher in the reference than in the treatment sections of both lakes. Average aquatic consumer allochthony per lake section was 27–40%, although terrestrial POC contributed less than about 10% to total organic C supply to the lakes. The production of aquatic consumers incorporated less than 5% of the total organic C supply in both lakes, indicating a low ecological efficiency. We suggest that the consumption of terrestrial POC by aquatic consumers facilitates a strong coupling with the terrestrial environment. However, the high autochthonous production and the large pool of autochthonous detritus in these nutrient-rich lakes make terrestrial POC quantitatively unimportant for the C flows within food webs.

National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-264656 (URN)10.1007/s10021-015-9933-2 (DOI)000371797400007 ()
Available from: 2015-10-15 Created: 2015-10-15 Last updated: 2017-12-01Bibliographically approved
Hilt, S., Wanke, T., Scharnweber, K., Brauns, M., Syväranta, J., Brothers, S., . . . Mehner, T. (2015). Contrasting response of two shallow eutrophic cold temperate lakes to a partial winterkill of fish. Hydrobiologia, 749(1), 31-42
Open this publication in new window or tab >>Contrasting response of two shallow eutrophic cold temperate lakes to a partial winterkill of fish
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2015 (English)In: Hydrobiologia, ISSN 0018-8158, E-ISSN 1573-5117, Vol. 749, no 1, p. 31-42Article in journal (Refereed) Published
Abstract [en]

Food-web effects of winterkill are difficult to predict as the enhanced mortality of planktivorous fish may be counterbalanced by an even higher mortality of piscivores. We hypothesised that a winterkill in a clear and a turbid shallow lake would equalise their fish community composition, but seasonal plankton successions would differ between lakes. After a partial winterkill, we observed a reduction of fish biomass by 16 and 43% in a clear-water and a turbid small temperate lake, respectively. Fish biomass and piscivore shares (5% of fish biomass) were similar in both lakes after this winterkill, but young-of-the-year (YOY) abundances were higher in the turbid lake. Top-down control by crustaceans was only partly responsible for low phytoplankton biomass at the end of May following the winterkill in both lakes. Summer phytoplankton biomass remained low in the clear-water lake despite high abundances of YOY fish (mainly roach). In contrast, the crustacean biomass of the turbid lake was reduced in summer by a high YOY abundance (sunbleak and roach), leading to a strong increase in phytoplankton biomass. The YOY abundance of fish in shallow eutrophic lakes may thus be more important for their summer phytoplankton development after winterkill than the relative abundance of piscivores.

National Category
Biological Sciences
Identifiers
urn:nbn:se:uu:diva-246053 (URN)10.1007/s10750-014-2143-7 (DOI)000349968400003 ()
Available from: 2015-03-02 Created: 2015-03-02 Last updated: 2017-12-04Bibliographically approved
Tobler, M., Scharnweber, K., Greenway, R., Passow, C. N., Arias-Rodriquez, L. & García-De-León, F. J. (2015). Convergent changes in the trophic ecology of extremophile fish occurring along replicated environmental gradients. Freshwater Biology, 60(4), 768-780
Open this publication in new window or tab >>Convergent changes in the trophic ecology of extremophile fish occurring along replicated environmental gradients
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2015 (English)In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 60, no 4, p. 768-780Article in journal (Refereed) Published
Abstract [en]

Divergent selection along environmental gradients connecting locally restricted extreme habitats and adjacent benign habitats can shape convergent evolution of traits involved in coping with physiochemical stressors and can drive speciation. At the same time, the presence of such stressors alters aspects of the biotic environment, including resource availability and competitive regimes. However, it remains unclear whether and how the ecology of populations occurring in both extreme and benign environments varies in a predictable fashion. We investigated the trophic ecology of live-bearing fishes of the genus Poecilia that have independently colonised multiple springs containing toxic hydrogen sulphide in southern Mexico. Sulphide spring fish are adapted to the unique environmental conditions and are reproductively isolated from ancestral populations in adjacent non-sulphidic habitats. We used gut content analyses to test whether colonisation of extreme habitats was accompanied by shifts of trophic resource use and expansions of trophic niche width. Furthermore, we tested whether dietary shifts were reflected in trophic morphology by comparing intestinal tract lengths among populations using both wild-caught and common garden-raised individuals. Gut content analyses revealed that fish inhabiting toxic springs expanded their trophic niche width and changed their dietary resource use from detritus and algae to sulphide bacteria and invertebrates. This dietary shift was paralleled by changes in intestinal tract morphology, whereby sulphide spring fish had shorter intestines than fish from adjacent non-sulphidic habitats. Analysis of common garden-raised fish indicated that morphological differences between sulphidic and non-sulphidic populations are at least in part due to genetic differentiation. Both patterns of trophic resource use and differentiation in trophic morphology were consistent across replicated pairs of sulphidic and non-sulphidic populations, although the magnitude of differentiation varied among river drainages. Our results suggest that colonisation of and adaptation to sulphide springs in southern Mexico was paralleled by convergent changes in trophic ecology. This highlights the complexity of environmental gradients and the necessity of considering multiple sources of selection when studying the evolution of complex phenotypes.

Keywords
dietary niche, ecological diversification, extreme environment, hydrogen sulphide springs, Poecilia (Poeciliidae)
National Category
Ecology
Identifiers
urn:nbn:se:uu:diva-246056 (URN)10.1111/fwb.12530 (DOI)000351213000014 ()
Available from: 2015-03-02 Created: 2015-03-02 Last updated: 2017-12-04Bibliographically approved
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