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  • 1. Brothers, Soren
    et al.
    Köhler, Jan
    Attermeyer, Katrin
    Grossart, Hans-Peter
    Mehner, Thomas
    Meyer, Nils
    Scharnweber, Kristin
    Hilt, Sabine
    A feedback loop links brownification and anoxia in a temperate, shallow lake2014In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 59, no 4, p. 1388-1398Article in journal (Refereed)
    Abstract [en]

    This study examines a natural, rapid, fivefold increase in dissolved organic carbon (DOC) concentrations in a temperate shallow lake, describing the processes by which increased DOC resulted in anoxic conditions and altered existing carbon cycling pathways. High precipitation for two consecutive years led to rising water levels and the flooding of adjacent degraded peatlands. Leaching from the flooded soils provided an initial increase in DOC concentrations (from a 2010 mean of 12 ± 1 mg L−1 to a maximum concentration of 53 mg L−1 by June 2012). Increasing water levels, DOC, and phytoplankton concentrations reduced light reaching the sediment surface, eliminating most benthic primary production and promoting anoxia in the hypolimnion. From January to June 2012 there was a sudden increase in total phosphorus (from 57 µg L−1 to 216 µg L−1), DOC (from 24.6 mg L−1 to 53 mg L−1), and iron (from 0.12 mg L−1 to 1.07 mg L−1) concentrations, without any further large fluxes in water levels. We suggest that anoxic conditions at the sediment surface and flooded soils produced a dramatic release of these chemicals that exacerbated brownification and eutrophication, creating anoxic conditions that persisted roughly 6 months below a water depth of 1 m and extended periodically to the water surface. This brownification-anoxia feedback loop resulted in a near-complete loss of macroinvertebrate and fish populations, and increased surface carbon dioxide (CO2) emissions by an order of magnitude relative to previous years.

  • 2. Brothers, Soren M
    et al.
    Hilt, Sabine
    Attermeyer, Katrin
    Grossart, Hans Peter
    Kosten, Sarian
    Lischke, Betty
    Mehner, Thomas
    Meyer, Nils
    Scharnweber, Kristin
    Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Berlin.
    Köhler, Jan
    A regime shift from macrophyte to phytoplankton dominance enhances carbon burial in a shallow, eutrophic lake2013In: Ecosphere, ISSN 2150-8925, E-ISSN 2150-8925, Vol. 4, no 11, article id 137Article in journal (Refereed)
    Abstract [en]

    Ecological regime shifts and carbon cycling in aquatic systems have both been subject to increasing attention in recent years, yet the direct connection between these topics has remained poorly understood. A four-fold increase in sedimentation rates was observed within the past 50 years in a shallow eutrophic lake with no surface in- or outflows. This change coincided with an ecological regime shift involving the complete loss of submerged macrophytes, leading to a more turbid, phytoplankton-dominated state. To determine whether the increase in carbon (C) burial resulted from a comprehensive transformation of C cycling pathways in parallel to this regime shift, we compared the annual C balances (mass balance and ecosystem budget) of this turbid lake to a similar nearby lake with submerged macrophytes, a higher transparency, and similar nutrient concentrations. C balances indicated that roughly 80% of the C input was permanently buried in the turbid lake sediments, compared to 40% in the clearer macrophyte-dominated lake. This was due to a higher measured C burial efficiency in the turbid lake, which could be explained by lower benthic C mineralization rates. These lower mineralization rates were associated with a decrease in benthic oxygen availability coinciding with the loss of submerged macrophytes. In contrast to previous assumptions that a regime shift to phytoplankton dominance decreases lake heterotrophy by boosting whole-lake primary production, our results suggest that an equivalent net metabolic shift may also result from lower C mineralization rates in a shallow, turbid lake. The widespread occurrence of such shifts may thus fundamentally alter the role of shallow lakes in the global C cycle, away from channeling terrestrial C to the atmosphere and towards burying an increasing amount of C.

  • 3. Hilt, Sabine
    et al.
    Wanke, Thomas
    Scharnweber, Kristin
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Brauns, Mario
    Syväranta, Jari
    Brothers, Soren
    Gaedke, Ursula
    Köhler, Jan
    Lischke, Betty
    Mehner, Thomas
    Contrasting response of two shallow eutrophic cold temperate lakes to a partial winterkill of fish2015In: Hydrobiologia, ISSN 0018-8158, E-ISSN 1573-5117, Vol. 749, no 1, p. 31-42Article in journal (Refereed)
    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.

  • 4. Lischke, Betty
    et al.
    Attermeyer, Katrin
    Brauns, Mario
    Brothers, Soren
    Hilt, Sabine
    Grossart, Hans-Peter
    Köhler, Jan
    Mehner, Thomas
    Scharnweber, Kristin
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Gaedke, Ursula
    A dominance of pelagic carbon fluxes in shallow lake food webs emerges from the inefficient transfer of benthic carbonArticle in journal (Refereed)
  • 5. Lischke, Betty
    et al.
    Mehner, Thomas
    Hilt, Sabine
    Attermeyer, Katrin
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology. Leibniz Inst Freshwater Ecol & Inland Fisheries, Stechlin, Germany.
    Brauns, Mario
    Brothers, Soren
    Grossart, Hans Peter
    Köhler, Jan
    Scharnweber, Kristin
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology. Leibniz Inst Freshwater Ecol & Inland Fisheries, Berlin, Germany.
    Gaedke, Ursula
    Benthic carbon is inefficiently transferred in the food webs of two eutrophic shallow lakes2017In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 62, no 10, p. 1693-1706Article in journal (Refereed)
    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

  • 6. Lischke, Betty
    et al.
    Weithoff, Guntram
    Wickham, Stephen
    Attermeyer, Katrin
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Grossart, Hans-Peter
    Scharnweber, Kristin
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Hilt, Sabine
    Gaedke, Ursula
    Large biomass of small feeders: Ciliates may dominate herbivory in eutrophic lakes2016In: Journal of Plankton Research, ISSN 0142-7873, E-ISSN 1464-3774, Vol. 38, no 1, p. 2-15Article in journal (Refereed)
    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.

  • 7.
    Marklund, Maria H. K.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology. School of Biological Sciences and The Environment Institute, University of Adelaide, North Terrace, SA 5005, Australia.
    Svanbäck, R.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology.
    Faulks, Leanne
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology. Sugadaira Montane Research Center, University of Tsukuba, Sugadairakogen 1278-294, Ueda, Nagano 386-2204, Japan.
    Breed, Martin
    School of Biological Sciences and The Environment Institute, University of Adelaide, North Terrace, SA 5005, Australia.
    Scharnweber, Kristin
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Zha, Yinghua
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Eklöv, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Asymmetrical habitat coupling of a top predatorManuscript (preprint) (Other academic)
  • 8.
    Marklund, Maria H. K.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology. Water Research Centre and The Environment Institute, School of Biological Sciences, Univ. of Adelaide, North Terrace, SA, Australia.
    Svanbäck, Richard
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology.
    Zha, Yinghua
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Scharnweber, Kristin
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Eklöv, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    The influence of habitat accessibility on the dietary and morphological specialisation of an aquatic predator2018In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 127, no 1, p. 160-169Article in journal (Refereed)
    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.

  • 9. Mehner, Thomas
    et al.
    Attermeyer, Katrin
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Brauns, Mario
    Brothers, Soren
    Diekmann, Jochen
    Gaedke, Ursula
    Grossart, Hans-Peter
    Köhler, Jan
    Lischke, Betty
    Meyer, Nils
    Scharnweber, Kristin
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Syväranta, Jari
    Vanni, Michael J.
    Hilt, Sabine
    Weak response of animal allochthony and production to enhanced supply of terrestrial leaf litter in nutrient-rich lakes2016In: Ecosystems (New York. Print), ISSN 1432-9840, E-ISSN 1435-0629, Vol. 19, no 2, p. 311-325Article in journal (Refereed)
    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.

  • 10.
    Mikolajewski, Dirk Johannes
    et al.
    Free Univ Berlin, Inst Biol, Berlin, Germany.
    Scharnweber, Kristin
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Jiang, B
    Free Univ Berlin, Inst Biol, Berlin, Germany.
    Leicht, Sebastian
    Free Univ Berlin, Inst Biol, Berlin, Germany.
    Mauersberger, Rüdiger
    Forderverein Feldberg Uckermark Seenlandschaft eV, Templin, Germany.
    Johansson, Frank
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics.
    Changing the habitat: the evolution of inter-correlated traits to escape from predators2016In: Journal of Evolutionary Biology, ISSN 1010-061X, E-ISSN 1420-9101, Vol. 29, no 7, p. 1394-1405Article in journal (Refereed)
    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.

  • 11. Riesch, Rüdiger
    et al.
    Duwe, Virginia
    Herrmann, Nina
    Padur, Lisa
    Ramm, Annemarie
    Scharnweber, Kristin
    Unit of Animal Ecology, University of Potsdam.
    Schulte, Matthias
    Schulz-Mirbach, Tanja
    Ziege, Madlen
    Plath, Martin
    Variation along the shy-bold continuum in extremophile fishes (Poecilia mexicana, Poecilia sulphuraria)2009In: Behavioral Ecology and Sociobiology, ISSN 0340-5443, E-ISSN 1432-0762, Vol. 63, no 10, p. 1515-1526Article in journal (Refereed)
    Abstract [en]

    One potential trade-off that bold individuals face is between increased predation risks and gains in resources. Individuals experiencing high predation and hungry individuals (or individuals with low body condition) are predicted to show increased boldness. We examined one behavioral trait previously reported to be associated with boldness (the time individual fish needed to emerge from shelter) in various populations of mollies (Poecilia spp.). Our study system included several southern Mexican surface streams with high piscine predation and high food availability, sulfidic surface streams with high avian predation, in which the inhabiting fish show reduced body condition, and a sulfidic cave, where predation and body condition are low. Our comparison revealed very short times to emerge from the start box in populations from non-sulfidic streams. In sulfidic habitats (whether surface or cave), it took individual Poecilia mexicana considerably longer to emerge from the start box, and the same difference was also found in an independent comparison between P. mexicana and the closely related, highly sulfide-adapted Poecilia sulphuraria. Fish reared under common garden conditions (in the absence of predators and hydrogen sulfide) showed intermediate boldness scores to the extremes observed in the field. Our data thus indicate that (a) boldness is shaped by environmental conditions/experiential effects, but is not heritable, (b) predation affects boldness in the predicted direction, but (c) low body condition leads to reduced boldness. Extremophile Poecilia spp. spend most of their time surfacing to survive under sulfidic and hypoxic conditions, which exposes them to increased levels of predations, but the fish forage on the bottom. Hence, in this system, increased boldness does not increase foraging success. We argue that energy limitation favors reducing energetically costly behaviors, and exploring novel environments may be just one of them.

  • 12.
    Scharnweber, Kristin
    et al.
    Department of Biology and Ecology of Fishes, Leibniz Institute of Freshwater Ecology & Inland Fisheries, Berlin.
    Plath, Martin
    Tobler, Michael
    Examination of boldness traits in sexual and asexual mollies (Poecilia latipinna, P. formosa)2011In: Acta Ethologica, ISSN 0873-9749, E-ISSN 1437-9546, Vol. 14, no 2, p. 77-83Article in journal (Refereed)
    Abstract [en]

    Considering the high costs of sexual reproduction (e.g., the production of males), its maintenance and predominance throughout the Animal Kingdom remain elusive. Especially the mechanisms allowing for a stable coexistence of closely related sexual and asexual species are still subject to a lively debate. Asexuals should rapidly outnumber sexuals due to higher population growth rates, unless they face some disadvantages. Here, we investigate potential differences in feeding behavior in a system of sexual (sailfin mollies, Poecilia latipinna) and coexisting gynogenetic fishes (Amazon mollies, Poecilia formosa). In two different experiments, we tested for differences in behavioral traits associated with boldness. Bold individuals take higher risks for gains in resources, so shyer individuals should be less competitive. Our study was motivated by the recent finding that P. formosa are less likely to be preyed upon by piscine predators than P. latipinna. We asked whether this result is indicative of low boldness in P. formosa. However, no differences between the two species were detectible in our behavioral experiments measuring (a) time to emerge from shelter to explore a novel environment, (b) latency time until feeding in a novel environment, and (c) recovery time until feeding restarted after a simulated predator attack. Furthermore, different boldness measures were not correlated with each other within individuals.

  • 13.
    Scharnweber, Kristin
    et al.
    Department of Biology and Ecology of Fishes, Leibniz Institute of Freshwater Ecology & Inland Fisheries, Berlin.
    Plath, Martin
    Tobler, Michael
    Feeding efficiency and food competition in coexisting sexual and asexual livebearing fishes of the genus Poecilia2011In: Environmental Biology of Fishes, ISSN 0378-1909, E-ISSN 1573-5133, Vol. 90, no 2, p. 197-205Article in journal (Refereed)
    Abstract [en]

    Considering its immediate costs of producing dispensable males, the maintenance of sexual reproduction is a major paradox in evolutionary biology. Asexual lineages that do not face such costs theoretically should replace sexuals over time. Nonetheless, several systems are known in which closely related sexual and asexual lineages stably coexist. In the present study, we studied a sexual/asexual mating complex of a sperm-dependent parthenogenetic fish (amazon molly, Poecilia formosa) and its sexual congeners, the sailfin molly P. latipinna and the Atlantic molly P. mexicana. We asked whether differences in feeding behavior could contribute to their stable coexistence. We conducted a laboratory experiment to compare feeding efficiencies and also measured the competitive abilities between the two reproductive forms. Additionally, we measured gut fullness of fishes caught in natural habitats. Contrary to our predictions, we could not find P. formosa to be less efficient in feeding. We argue that food competition in mollies plays a minor role in mediating coexistence between closely related asexual and sexual mollies.

  • 14.
    Scharnweber, Kristin
    et al.
    Leibniz Institute of Freshwater Ecology & Inland Fisheries, Department of Biology and Ecology of Fishes, Berlin.
    Plath, Martin
    Tobler, Michael
    Trophic niche segregation between the sexes in two species of livebearing fishes (Poeciliidae)2011In: Bulletin of Fish Biology, ISSN 1867-5417, Vol. 13, no 1-2, p. 11-20Article in journal (Refereed)
    Abstract [en]

    Fishes of the genus Poecilia are highly sexually dimorphic. In the two species investigated here (P. latipinna and P. mexicana) males are, on average, of smaller body size and more colorful than females. Males also differ from females in time allocated to feeding as they engage in mating behavior almost dayround. We hypothesized that, due to different time allocations and energy requirements, the sexes might forage on different food items and thus could occupy different trophic niches. We investigated gut content compositions, intestinal tract length and gut fullness in multiple populations of P. latipinna and P. mexicana. Our fi nding of females having fuller guts than males corroborated sex differences in time allocation for foraging. A major difference between sexes was also found in intestinal tract length, with males consistently having shorter guts, likely refl ecting spatial constraints due to sexually dimorphic traits (like a more anterior anal porus). Contrary to prediction, however, gut content composition indicated no clear-cut pattern of sex-specifi c trophic niches across study sites. Niche widths, on the other hand, differed between sexes with males having narrower trophic niches than females. Overall, we found sex-specifi c differences in some aspects of feeding ecology, but no clear trophic niche segregation was detected.

  • 15.
    Scharnweber, Kristin
    et al.
    Department of Biology and Ecology of Fishes, Leibniz Institute of Freshwater Ecology andInland Fisheries, Berlin.
    Plath, Martin
    Winemiller, Kirk
    Tobler, Michael
    Dietary niche overlap in sympatric asexual and sexual livebearing fishes Poecilia spp.2011In: Journal of Fish Biology, ISSN 0022-1112, E-ISSN 1095-8649, Vol. 79, no 7, p. 1760-1773Article in journal (Refereed)
    Abstract [en]

    The present study investigated the spatiotemporal patterns in trophic resource use in a system of a gynogenetic poeciliid fish, the Amazon molly Poecilia formosa, and its sexual congeners the sailfin molly Poecilia latipinna and the Atlantic molly Poecilia mexicana using gut contents analysis. No statistically significant differences in trophic resource use were found between sexual and gynogenetic species, but gut contents varied significantly across sites and over time. In addition, variation in trophic morphology (i.e. gut length) was significant across sites but not species, and laboratory experiments indicated that gut length is phenotypically plastic. Overall, trophic differentiation between coexisting asexual and sexual Poecilia appears to be minimal, and it is unlikely that niche differentiation contributes to a stable coexistence of the two reproductive forms.

  • 16.
    Scharnweber, Kristin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Strandberg, Ursula
    Univ Eastern Finland, Dept Biol, Joensuu, Finland.
    Karlsson, Konrad
    Stockholm Univ, Dept Ecol Environm & Plant Sci, Stockholm, Sweden.
    Eklöv, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Decrease of population divergence in Eurasian perch (Perca fluviatilis) in browning waters: role of fatty acids and foraging efficiency2016In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 11, no 9, article id e0162470Article in journal (Refereed)
    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.

  • 17.
    Scharnweber, Kristin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Strandberg, Ursula
    Univ Eastern Finland, Dept Biol, Yliopistokatu 7,POB 111, Joensuu 80101, Finland; Ryerson Univ, Dept Biol & Chem, 350 Victoria St, Toronto, ON M5B 2K3, Canada.
    Marklund, Maria Helena Katarina
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology. Univ Adelaide, Inst Environm, Water Res Ctr, Dept Earth & Environm Sci, Adelaide, SA 5005, Australia.
    Eklöv, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Combining resource use assessment techniques reveals trade-offs in trophic specialization of polymorphic perch2016In: Ecosphere, ISSN 2150-8925, E-ISSN 2150-8925, Vol. 7, no 8, article id e01387Article in journal (Refereed)
    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.

  • 18.
    Scharnweber, Kristin
    et al.
    Leibniz-Institute of Freshwater Biology and Inland Fisheries, Berlin.
    Syväranta, Jari
    Hilt, Sabine
    Brauns, Mario
    Vanni, M.J.
    Brothers, Soren
    Köhler, Jan
    Knežević-Jarić, Jelena
    Mehner, Thomas
    Whole-lake experiments reveal the fate of terrestrial particulate organic carbon in benthic food webs of shallow lakes2013In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 95, no 6, p. 1496-1505Article in journal (Refereed)
    Abstract [en]

    Lake ecosystems are strongly linked to their terrestrial surroundings by material and energy fluxes across ecosystem boundaries. However, the contribution of terrestrial particulate organic carbon (tPOC) from annual leaf fall to lake food webs has not yet been adequately traced and quantified. In this study, we conducted whole-lake experiments to trace artificially added tPOC through the food webs of two shallow lakes of similar eutrophic status, but featuring alternative stable regimes (macrophyte rich vs. phytoplankton dominated). Lakes were divided with a curtain, and maize (Zea mays) leaves were added, as an isotopically distinct tPOC source, into one half of each lake. To estimate the balance between autochthonous carbon fixation and allochthonous carbon input, primary production and tPOC and tDOC (terrestrial dissolved organic carbon) influx were calculated for the treatment sides. We measured the stable isotope ratios of carbon (δ13C) of about 800 samples from all trophic consumer levels and compared them between lake sides, lakes, and three seasons. Leaf litter bag experiments showed that added maize leaves were processed at rates similar to those observed for leaves from shoreline plants, supporting the suitability of maize leaves as a tracer. The lake-wide carbon influx estimates confirmed that autochthonous carbon fixation by primary production was the dominant carbon source for consumers in the lakes. Nevertheless, carbon isotope values of benthic macroinvertebrates were significantly higher with maize additions compared to the reference side of each lake. Carbon isotope values of omnivorous and piscivorous fish were significantly affected by maize additions only in the macrophyte-dominated lake and δ13C of zooplankton and planktivorous fish remained unaffected in both lakes. In summary, our results experimentally demonstrate that tPOC in form of autumnal litterfall is rapidly processed during the subsequent months in the food web of shallow lakes and is channeled to secondary and tertiary consumers predominantly via the benthic pathways. A more intense processing of tPOC seems to be connected to a higher structural complexity in littoral zones, and hence may differ between shallow lakes of alternative stable states.

  • 19.
    Scharnweber, Kristin
    et al.
    Leibniz-Inst. of Freshwater Ecology and Inland Fisheries.
    Vanni, M.J.
    Hilt, Sabine
    Syväranta, J
    Mehner, Thomas
    Boomerang ecosystem fluxes: organic carbon inputs from land to lakes are returned to terrestrial food webs via aquatic insects2014In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 123, no 12, p. 1439-1448Article in journal (Refereed)
    Abstract [en]

    Many ecosystems are linked to their adjacent ecosystems by movements of organisms. For instance, aquatic and terrestrial ecosystems are linked via emerging aquatic insects that serve as prey for terrestrial consumers. However, the role of these organisms in returning recycled carbon to the ecosystem from which it originated is not well known. This is due to the fact that values of carbon isotope signatures from terrestrial leaves and aquatic resources are usually similar and hence results of isotope mixing models need to be considered with caution. We overcame this problem by adding isotopically distinct terrestrial particulate organic carbon (tPOC) as a tracer to the experimental sides of two lakes that were divided in two equal halves with plastic curtains. We focused on aquatic insect larvae (Chironomidae) that fed on maize Zea mays leaves experimentally added to the lakes, and subsequently became prey for terrestrial predators (spiders) after emergence. The carbon isotope values of Chironomidae and spiders were significantly elevated in the lake treatment sides as compared to reference sides, whereas the values of all autochthonous resources were not affected by maize additions. Estimates from stable isotope mixing models indicated a low but demonstrable contribution of maize leaves to the diet of Chironomidae. Overlap between the isotope values of alder leaves, the major natural tPOC source, and autochthonous resources prevented a reliable quantification of allochthony of Chironomidae. However, we qualitatively demonstrated the flow of terrestrial particulate organic carbon to lakes, as leaf fall, and back to terrestrial surroundings via emerging insects. This ‘boomerang’ carbon flux between land and lakes blurs the distinction between autochthonous and allochthonous carbon sources.

  • 20.
    Scharnweber, Kristin
    et al.
    Department of Biology and Ecology of Fishes, Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Berlin.
    Watanabe, Kozo
    Syväranta, Jari
    Wanke, Thomas
    Monaghan, Michael T
    Mehner, Thomas
    Effects of predation pressure and resource use on morphological divergence in omnivorous prey fish2013In: BMC Evolutionary Biology, ISSN 1471-2148, E-ISSN 1471-2148, Vol. 13, article id 132Article in journal (Refereed)
    Abstract [en]

    Background

    Body shape is one of the most variable traits of organisms and responds to a broad array of local selective forces. In freshwater fish, divergent body shapes within single species have been repeatedly observed along the littoral-pelagic axes of lakes, where the structural complexity of near shore habitats provides a more diverse set of resources compared to the open-water zones. It remains poorly understood whether similar resource-driven polymorphism occurs among lakes that vary in structural complexity and predation pressure, and whether this variation is heritable. Here, we analyzed body shape in four populations of omnivorous roach (Rutilus rutilus) inhabiting shallow lakes. We tested the relationship between body shape, gradients of resources, predation pressure, and, in a subset of two lakes, diet composition. We used genome scans of 331 polymorphic AFLP markers to test whether there was a heritable component to the observed morphological diversification.

    Results

    Body shape differed among lakes and was significantly correlated to differences in predation pressure. Roach from the lake with highest predation pressure were most divergent from the average body shape of all populations, characterized by a more streamlined body and caudally inserted dorsal fins; features that facilitate predator escape. Surprisingly, diet composition was not associated with morphology. AFLP analysis revealed weak genetic differentiation among lakes and no isolation by distance (IBD). Outlier analysis detected three loci under positive selection with differing frequencies in the four populations. General linear models did not support an association of lake-specific genotypes with morphological variation.

    Conclusion

    Body shape was divergent among lakes, suggesting that processes previously reported from within single lakes may also be operating at the scale of whole lakes. We found no evidence for body shape being heritable, although sample size was small in these natural populations. Rather than habitat structure and diet, we conclude that predation had a stronger effect on the prevalence of local morphotypes. A variable morphotype facilitating the efficient uptake of a variety of spatially and temporarily scattered resources seems to be favored in these small aquatic systems.       

  • 21.
    Syväranta, Jari
    et al.
    Leibniz-Institute of Freshwater Biology and Inland Fisheries, Berlin, Germany.
    Scharnweber, Kristin
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology. Leibniz-Institute of Freshwater Biology and Inland Fisheries, Berlin, Germany.
    Brauns, Mario
    Leibniz-Institute of Freshwater Biology and Inland Fisheries, Berlin, Germany.
    Hilt, Sabine
    Leibniz-Institute of Freshwater Biology and Inland Fisheries, Berlin, Germany.
    Mehner, Thomas
    Leibniz-Institute of Freshwater Biology and Inland Fisheries, Berlin, Germany.
    Assessing the utility of hydrogen, carbon and nitrogen stable isotopes in estimating consumer allochthony in two shallow eutrophic lakes2016In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 11, no 5, article id e0155562Article in journal (Refereed)
    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.

  • 22. Tobler, Michael
    et al.
    Scharnweber, Kristin
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Greenway, Ryan
    Passow, Courtney N.
    Arias-Rodriquez, Lenin
    García-De-León, Francisco J.
    Convergent changes in the trophic ecology of extremophile fish occurring along replicated environmental gradients2015In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 60, no 4, p. 768-780Article in journal (Refereed)
    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.

  • 23. Ziege, Madlen
    et al.
    Padur, Lisa
    Duwe, Virginia
    Ramm, Annemarie
    Scharnweber, Kristin
    Unit of Animal Ecology, Institute of Biochemistry and Biology, University of Potsdam.
    Riesch, Rüdiger
    Plath, Martin
    Audience effect alters mate choice in male Heterophallus milleri (Poeciliidae)2008In: Bulletin of Fish Biology, ISSN 1867-5417, Vol. 10, no 1-2, p. 87-92Article in journal (Refereed)
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