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  • 1.
    Andersson, Jens
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Byström, Pär
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Claessen, D
    Persson, Lennart
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    De Roos, A. M.
    Stabilization of population fluctuations due to cannibalism promotes resource polymorphism in fish2007In: American Naturalist, Vol. 169, 820-829 p.Article in journal (Refereed)
  • 2.
    Ask, Jenny
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Karlsson, Jan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Persson, Lennart
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Ask, Per
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Byström, Pär
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jansson, Mats
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Terrestrial organic matter and light penetration: Effects on bacterial and primary production in lakes2009In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 54, no 6, 2034-2040 p.Article in journal (Refereed)
    Abstract [en]

    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.

  • 3.
    Ask, Jenny
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Karlsson, Jan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Persson, Lennart
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Ask, Per
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Byström, Pär
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jansson, Mats
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Whole-lake estimates of carbon flux through algae and bacteria in benthic and pelagic habitats of clear-water lakes2009In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 90, no 7, 1923-1932 p.Article in journal (Refereed)
    Abstract [en]

    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.

  • 4.
    Ask, Per
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Ask, Jenny
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Byström, Pär
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jansson, Mats
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Karlsson, Jan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Persson, Lennart
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Competition mediated coexistence of invading intermediate consumer, ninespine stickleback, and a resident omnivorous top predator, Arctic charManuscript (preprint) (Other academic)
    Abstract [en]

    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.

  • 5.
    Ask, Per
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Ask, Jenny
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Byström, Pär
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jansson, Mats
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Karlsson, Jan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Persson, Lennart
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Temperature mediated effects on top consumer populations in subarctic lakesManuscript (preprint) (Other academic)
    Abstract [en]

    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.

  • 6.
    Byström, P
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Andersson, J
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Size-dependent foraging capacities and intercohort competition in an ontogenetic omnivore (Arctic char)2005In: Oikos, Vol. 110, 523-536 p.Article in journal (Refereed)
  • 7.
    Byström, P
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Andersson, J
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Persson, L
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    De Roos, A M
    Size-dependent resource limitation and foraging-predation risk trade-offs: growth and habitat use in young arctic char2004In: Oikos, Vol. 104, 109-121 p.Article in journal (Refereed)
  • 8.
    Byström, Pär
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Recruitment pulses induce cannibalistic giants in Arctic char.2006In: J Anim Ecol, ISSN 0021-8790, Vol. 75, no 2, 434-44 p.Article in journal (Refereed)
  • 9.
    Byström, Pär
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Andersson, J
    Kiessling, A
    Eriksson, L O
    Size and temperature dependent foraging capacities and metabolism: consequences for winter starvation mortality in fish2006In: Oikos, Vol. 115, 43-52 p.Article in journal (Refereed)
  • 10.
    Byström, Pär
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Ask, Per
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Andersson, Jens
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Persson, Lennart
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Preference for cannibalism and ontogenetic constraints in competitive ability of piscivorous top predators2013In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 8, no 7, e70404- p.Article in journal (Refereed)
    Abstract [en]

    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.

  • 11.
    Byström, Pär
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Bergström, Ulf
    Hjälten, Alexander
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Ståhl, Sofie
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jonsson, David
    Olsson, Jens
    Declining coastal piscivore populations in the Baltic Sea: where and when do sticklebacks matter?2015In: Ambio, ISSN 0044-7447, E-ISSN 1654-7209, Vol. 44, no Suppl 3, S462-S471 p.Article in journal (Refereed)
    Abstract [en]

    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.

  • 12.
    Byström, Pär
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Huss, Magnus
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Persson, Lennart
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Ontogenetic constraints and diet shifts in Perch (Perca fluviatilis): mechanisms and consequences for intra-cohort cannibalism2012In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 57, no 4, 847-857 p.Article in journal (Refereed)
    Abstract [en]

    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.

  • 13.
    Byström, Pär
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Karlsson, Jan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Nilsson, Per
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Van Kooten, Tobias
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Ask, Jenny
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Olofsson, Frans
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Substitution of top predators: effects of pike invasion in a subarctic lake2007In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 52, no 7, 1271–1280- p.Article in journal (Refereed)
    Abstract [en]

    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.

  • 14. Calboli, Federico C. F.
    et al.
    Byström, Pär
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Merila, Juha
    A test for within-lake niche differentiation in the nine-spined sticklebacks (Pungitius pungitius)2016In: Ecology and Evolution, ISSN 2045-7758, E-ISSN 2045-7758, Vol. 6, no 14, 4753-4760 p.Article in journal (Refereed)
    Abstract [en]

    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.

  • 15.
    Degerman, Rickard
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Umeå University, Faculty of Science and Technology, Umeå Marine Sciences Centre (UMF).
    Lefébure, Robert
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Umeå University, Faculty of Science and Technology, Umeå Marine Sciences Centre (UMF).
    Byström, Pär
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Båmstedt, Ulf
    Umeå University, Faculty of Science and Technology, Umeå Marine Sciences Centre (UMF). Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Larsson, Stefan
    Umeå University, Faculty of Science and Technology, Umeå Marine Sciences Centre (UMF). Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Andersson, Agneta
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Umeå University, Faculty of Science and Technology, Umeå Marine Sciences Centre (UMF).
    Food web interactions determine energy transfer efficiency and top consumer responses to inputs of dissolved organic carbon2018In: Hydrobiologia, ISSN 0018-8158, E-ISSN 1573-5117, Vol. 805, no 1, 131-146 p.Article in journal (Refereed)
    Abstract [en]

    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).

  • 16.
    Diehl, Sebastian
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Thomsson, Gustaf
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Wickman, Jonas
    Umeå University, Faculty of Science and Technology, Department of Mathematics and Mathematical Statistics.
    Vasconcelos, Francisco R.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Uszko, Wojciech
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Ask, Jenny
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Karlsson, Jan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Byström, Pär
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Resource and consumer control of cross-habitat trophic interactions in shallow lakesManuscript (preprint) (Other academic)
  • 17.
    Huss, Magnus
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Byström, Pär
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Persson, Lennart
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Effects of ontogenetic scaling on resource exploitation and cohort size distributions2010In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 119, no 2, 384-392 p.Article in journal (Refereed)
    Abstract [en]

    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.

  • 18.
    Huss, Magnus
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Byström, Pär
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Persson, Lennart
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Growing through predation windows:: effects on body size development in young fish2010In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 119, 1796-1804 p.Article in journal (Refereed)
    Abstract [en]

    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.

  • 19.
    Huss, Magnus
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Byström, Pär
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Persson, Lennart
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Resource heterogeneity, diet shifts and intra-cohort competition: effects on size divergence in YOY fish2008In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 158, no 2, 249-257 p.Article in journal (Refereed)
    Abstract [en]

    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.

  • 20.
    Huss, Magnus
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Byström, Pär
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Strand, Åsa
    Eriksson, Lars-Ove
    Persson, Lennart
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Influence of growth history on the accumulation of energy reserves and winter mortality on young fish2008In: Canadian Journal of Fisheries and Aquatic Sciences, ISSN 0706-652X, E-ISSN 1205-7533, Vol. 65, no 10, 2149-2156 p.Article in journal (Refereed)
    Abstract [en]

    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.

  • 21.
    Huss, Magnus
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Persson, Lennart
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Byström, Pär
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    The origin and development of individual size variation in early pelagic stages of fish2007In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 153, no 1, 57-67 p.Article in journal (Refereed)
    Abstract [en]

    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.

  • 22.
    Jonsson, Micael
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Hedström, Per
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Stenroth, Karolina
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Hotchkiss, Erin R
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Vasconcelos, Francisco Rivera
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Karlsson, Jan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Byström, Pär
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Climate change modifies the size structure of assemblages of emerging aquatic insects2015In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 60, no 1, 78-88 p.Article in journal (Refereed)
    Abstract [en]

    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.

  • 23.
    Karlsson, J
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Byström, P
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Littoral energy mobilization dominates energy supply for top consumers in subarctic lakes2005In: Limnol. Oceanogr., Vol. 50, 538-543 p.Article in journal (Refereed)
  • 24.
    Karlsson, Jan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Berggren, M.
    Ask, Jenny
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Byström, Pär
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jonsson, Anders
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Laudon, H.
    Jansson, Mats
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Response to Comment: Terrestrial support of pelagic consumers in unproductive lakes- Uncertainty and potential in assessments using stable isotopes2014In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 59, no 5, 1800-1803 p.Article in journal (Refereed)
  • 25.
    Karlsson, Jan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Berggren, Martin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Ask, Jenny
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Byström, Pär
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jonsson, Anders
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Laudon, Hjalmar
    Jansson, Mats
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Terrestrial organic matter support of lake food webs: Evidence from lake metabolism and stable hydrogen isotopes of consumers2012In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 57, no 4, 1042-1048 p.Article in journal (Refereed)
    Abstract [en]

    We quantified the utilization of terrestrial organic matter (OM) in the food web of a humic lake by analyzing the metabolism and the consumers' stable isotopic (C, H, N) composition in benthic and pelagic habitats. Terrestrial OM inputs (3 g C m(-2) d(-1)) to the lake greatly exceeded autochthonous OM production (3 mg C m(-2) d(-1)) in the lake. Heterotrophic bacterial growth (19 mg C m(-2) d(-1)) and community respiration (115 mg C m(-2) d(-1)) were high relative to algal photosynthesis and were predominantly (> 85%) supported by terrestrial OM in both habitats. Consequently, terrestrial OM fueled most (85%) of the total production at the base of the lake's food web (i.e., the sum of primary and bacterial production). Despite the uncertainties of quantitatively estimating resource use based on stable isotopes, terrestrial OM clearly also supported around half the zooplankton (47%), macrozoobenthos (63%), and fish (57%) biomass. These results indicate that, although rates of terrestrial OM inputs were around three orders of magnitude greater than that of autochthonous OM production, the use of the two resources by higher trophic levels was roughly equal. The disproportionally low reliance on terrestrial OM at higher trophic levels, compared with its high rates of input and high support of basic biomass production in the lake, suggests that autochthonous resources could not be completely replaced by terrestrial resources and indicates an upper limit to terrestrial support of lake food webs.

  • 26.
    Karlsson, Jan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Bergström, Ann-Kristin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Byström, Pär
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Gudasz, Cristian
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Rodriguez, Patricia
    Hein, Catherine
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Terrestrial organic matter input suppresses biomass production in lake ecosystems2015In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 96, no 11, 2870-2876 p.Article in journal (Refereed)
    Abstract [en]

    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.

  • 27.
    Karlsson, Jan
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Byström, Pär
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Ask, Jenny
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Ask, Per
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Persson, Lennart
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Jansson, Mats
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Light limitation of nutrient-poor lake ecosystems2009In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 460, 506-509 p.Article in journal (Refereed)
    Abstract [en]

    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.

  • 28. Larsson, Stefan
    et al.
    Byström, Pär
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Berglund, Johnny
    Carlsson, Ulf
    Veneranta, Lari
    Larsson, Sylvia H.
    Hudd, Richard
    Characteristics of anadromous whitefish (Coregonus lavaretus (L.)) rivers in the Gulf of Bothnia2013In: BIOLOGY AND MANAGEMENT OF COREGONID FISHES - 2011, 2013, 189-201 p.Conference paper (Refereed)
    Abstract [en]

    In order to study anadromous whitefish spawning river requirements, we sampled 41 rivers in the Gulf of Bothnia for newly hatched whitefish larvae for one to three consecutive years. Chemical and morphological data (e.g. flow rate, topography, pH, estuary fetch and distance to coastal sandy areas) were collected for each river. Newly-hatched whitefish were caught in 19 rivers whereas whitefish were not confirmed present in 22 rivers. By applying partial least squares discriminant analysis (PLS-DA), data for rivers confirmed to support whitefish were contrasted with data for rivers in which whitefish were not found. The single most important factor was annual average water flow rate. Whitefish larvae were observed in 93% of the rivers with annual mean flow rate > 5 m(3) s(-1) (N = 14). In contrast, newly-hatched whitefish were only found in 22% of the smaller rivers (N = 27).

  • 29.
    Lefebure, Robert
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Umeå University, Faculty of Science and Technology, Umeå Marine Sciences Centre (UMF).
    Degerman, Rickard
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Umeå University, Faculty of Science and Technology, Umeå Marine Sciences Centre (UMF).
    Andersson, Agneta
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Larsson, Stefan
    Umeå University, Faculty of Science and Technology, Umeå Marine Sciences Centre (UMF).
    Eriksson, Lars-Ove
    Department of Wildlife, Fish and Environmental Studies, SLU, Umeå, Sweden.
    Båmstedt, Ulf
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Umeå University, Faculty of Science and Technology, Umeå Marine Sciences Centre (UMF).
    Byström, Pär
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Impacts of elevated terrestrial nutrient loads and temperature on pelagic food web efficiency and fish production2013In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 19, no 5, 1358-1372 p.Article in journal (Other academic)
    Abstract [en]

    Both temperature and terrestrial organic matter have strong impacts on aquatic food-web dynamics and production. Temperature affects vital rates of all organisms, and terrestrial organic matter can act both as an energy source for lower trophic levels, while simultaneously reducing light availability for autotrophic production. As climate change predictions for the Baltic Sea and elsewhere suggest increases in both terrestrial matter runoff and increases in temperature, we studied the effects on pelagic food-web dynamics and food-web efficiency in a plausible future scenario with respect to these abiotic variables in a large-scale mesocosm experiment. Total basal (phytoplankton plus bacterial) production was slightly reduced when only increasing temperatures, but was otherwise similar across all other treatments. Separate increases in nutrient loads and temperature decreased the ratio of autotrophic:heterotrophic production, but the combined treatment of elevated temperature and terrestrial nutrient loads increased both fish production and food-web efficiency. CDOM: Chl a ratios strongly indicated that terrestrial and not autotrophic carbon was the main energy source in these food webs and our results also showed that zooplankton biomass was positively correlated with increased bacterial production. Concomitantly, biomass of the dominant calanoid copepod Acartia sp. increased as an effect of increased temperature. As the combined effects of increased temperature and terrestrial organic nutrient loads were required to increase zooplankton abundance and fish production, conclusions about effects of climate change on food-web dynamics and fish production must be based on realistic combinations of several abiotic factors. Moreover, our results question established notions on the net inefficiency of heterotrophic carbon transfer to the top of the food web.

  • 30.
    Lefébure, Robert
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Umeå University, Faculty of Science and Technology, Umeå Marine Sciences Centre (UMF).
    Larsson, S
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Umeå University, Faculty of Science and Technology, Umeå Marine Sciences Centre (UMF).
    Byström, Pär
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    A temperature-dependent growth model for the three-spined stickleback Gasterosteus aculeatus2011In: Journal of Fish Biology, ISSN 0022-1112, E-ISSN 1095-8649, Vol. 79, no 7, 1815-1827 p.Article in journal (Refereed)
    Abstract [en]

    Specific growth rates of individually reared juvenile three-spined sticklebacks Gasterosteus aculeatus were investigated under laboratory conditions to parameterize a complete temperature-dependent growth model for this species. To test the applicability of experimentally derived optima in growth response rates to natural conditions, the effects of commercial pellets and natural prey on growth rates were investigated. In addition, to test for seasonal effects on growth, laboratory trials were performed in both spring and winter. Growth took place from 5 to 29° C with a temperature for optimum growth reaching a sharp peak at 21° C. Modelled optimal temperature for maximum growth was estimated to be 21.7° C and lower and upper temperatures for growth were estimated to be 3.6 and 30.7° C, respectively. There were no significant differences in growth rates between fish reared on invertebrates or commercial pellets. Seasonal effects on growth were pronounced, with reduced growth rates in the winter despite similar laboratory conditions. On average, 60% higher growth rates were achieved at the optimum temperature in summer compared to the winter. The strong seasonality in the growth patterns of G. aculeatus indicated here reduces the applicability of the model derived in this study to spring and summer conditions.

  • 31.
    Lefébure, Robert
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Umeå University, Faculty of Science and Technology, Umeå Marine Sciences Centre (UMF).
    Larsson, S.
    Umeå University, Faculty of Science and Technology, Umeå Marine Sciences Centre (UMF).
    Byström, Pär
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Temperature and size-dependent attack rates of the three-spined stickleback (Gasterosteus aculeatus): are sticklebacks in the Baltic Sea resource-limited?2014In: Journal of Experimental Marine Biology and Ecology, ISSN 0022-0981, E-ISSN 1879-1697, Vol. 451, 82-90 p.Article in journal (Refereed)
    Abstract [en]

    The three-spined stickleback Gasterosteus aculeatus is a small omnivorous fish, widely distributed in the northern hemisphere. In the Baltic Sea, recently observed increases in their population densities have been attributed to declines of piscivorous predators. Concurrent with this predator release, an alternative hypothesis is that past and present consumption rates and resource limitation thresholds may have contributed to the recent increases in stickleback abundance. To evaluate this hypothesis, we estimated the size- and temperature-dependent attack rate and the critical resource density (CRD) of three-spined sticklebacks. We incorporated laboratory results with time series of zooplankton abundance to estimate historical trends in degrees of resource limitation in sticklebacks and evaluate if increases in individual consumption rates could be a plausible mechanism facilitating the suggested population increase. Attack rates increased with body size and temperature in laboratory experiments. Estimated CRD increased with size but decreased with temperature, suggesting that stickleback scope for individual and population growth might increase at temperatures above 15 degrees C. Our results further suggest that sticklebacks have been living closer to maximum consumption capacity in the coastal areas of the Bothnian Sea (BS) and Bothnian Bay (BB). Moreover, decreasing levels of resource limitation in the corresponding off-shore zones may have facilitated increases in stickleback densities for these areas. However, in the coastal zones of the Baltic proper (BP), resource levels have declined and are approaching the CRD, suggesting that stickleback populations in BP may not increase further. The decrease in CRD with temperature implies that increasing summer temperatures will increase the scope of individual and population growth in the three-spined stickleback and may favor the three-spined stickleback's competitive ability over other species under a warmer climate. (C) 2013 Elsevier B.V. All rights reserved.

  • 32.
    Norlin, Linnea
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Byström, Pär
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Karlsson, Jan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Climate Impacts Research Centre (CIRC), Department of Ecology and Environmental Science, Umeå University, Abisko, Sweden.
    Johansson, Martin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Liess, Antonia
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Climate change will alter amphibian-mediated nutrient pathways: evidence from Rana temporaria tadpoles in experimental ponds2016In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 61, no 4, 472-485 p.Article in journal (Refereed)
    Abstract [en]

    1. With global warming, mean temperatures and brownification of many waterbodies are predicted to increase. This may have unknown consequences on aquatic consumer life histories and nutrient content, consumer-mediated nutrient recycling, and nutrient transport between water and land.

    2. Using a large-scale experimental pond facility, we altered temperature (ambient/+ 4 degrees C) and brownification (clear/humic) in a 2 x 2 factorial design (n = 16 pond sections) to test two aspects of climate change on Rana temporaria tadpole life-history traits and on tadpole-mediated nutrient pathways. On day 16 after hatching, we examined tadpole-mediated nutrient recycling by measuring tadpole nutrient excretion and egestion rates and tadpole body nutrient content. We estimated tadpole growth and development rates from hatching to emergence and measured emergent frog body size and body nutrient content.

    3. Brownification increased total pond water nutrient availability and total pond water nitrogen (N) : phosphorous (P) ratios. Warming positively affected tadpole growth and development rates, whereas browning increased tadpole growth rate only under ambient temperatures. Emergent frog body P content decreased with warming, but only in the clear treatments. But despite these variations in body nutrient content, body stoichiometry remained within a relatively narrow stoichiometric range for both emergent frogs (P content: 1.4-1.8%, N content: 11.4-11.8% and carbon [C] content: 46.9-51.3%) and tadpoles (P content: 1.1-1.2%, N content: 10.1-11.7% and C content: 48.0-50.5%). Warming increased tadpole body P content and browning had a positive effect on tadpole body N content and tadpole N excretion rates, probably mediated by the increased pond water total N availability.

    4. We conclude that warming and brownification will interact in changing aquatic consumer growth and body nutrient stoichiometry. In addition, warming has the potential to affect emergent frog body nutrient content and may thus affect nutrient transport from water to land. Last, by increasing pond water N availability, brownification appears to intensify consumer P limitation and thus amplify consumer-meditated N recycling.

  • 33.
    Persson, L
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Byström, P
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Wahlström, E
    Westman, E
    Trophic dynamics in a whole lake experiment: size-structured interactions and recruitment variation2004In: Oikos, Vol. 106, 263-274 p.Article in journal (Refereed)
  • 34.
    Persson, L
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Claessen, D
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    De Roos,, A M
    Byström, P
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Sjögren, S
    Svanbäck, Richard
    Wahlström, E
    Westman, E
    Cannibalism in a size-structured population: energy extraction and control2004In: Ecological Monographs, Vol. 74, 135-157 p.Article in journal (Refereed)
  • 35.
    Persson, Lennart
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    de Roos, André M
    Byström, Pär
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    State-dependent invasion windows for prey in size-structured predator–prey systems: whole lake experiments2007In: Journal of Animal Ecology, Vol. 76, no 1, 94-104 p.Article in journal (Refereed)
    Abstract [en]

    1.

    In size-structured communities where individuals grow in size over their life cycle, interactions between species will shift between competitive and predatory interactions depending on size relationships. The outcome of interactions will subsequently depend on the strength of competitive and predatory interactions, respectively.

    2.

    In a whole lake experiment including four experimental lakes, it was tested under which conditions the competing prey, roach Rutilus rutilus, could successfully recruit into systems previously occupied by the predator, perch Perca fluviatilis. Two replicated introduction experiments were carried out 3 years apart.

    3.

    Roach were able to successfully recruit into three of the four experimental lakes of which two were also inhabited by the top predator pike Esox lucius. Resource levels were unrelated to whether roach could successfully recruit into the systems as recruiting roach in all years were feeding close to their maximum rate.

    4.

    High population fecundity of roach and low predation pressure by perch combined were necessary ingredients for successful recruitment and the presence of only one of these conditions did not result in successful recruitment.

    5.

    It is hypothesized that, although roach were able to successfully recruit into one lake with only perch present in addition to the two lakes that also inhabited pike, long-term coexistence of roach and perch depends on the presence of another top predator (e.g. pike) selectively preying on perch. This hypothesis was supported by data on co-occurrence of perch and roach in different lakes.

    6.

    Overall, the results are in accordance with expectation of size-structured life-history omnivory theory suggesting that coexistence between top predator and intermediate consumer is fragile.

  • 36.
    van Kooten, Tobias
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Andersson, Jens
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Byström, Pär
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Persson, Lennart
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    de Roos, Andre M.
    Size at hatching determines population dynamics and response to harvesting in cannibalistic fish2010In: Canadian Journal of Fisheries and Aquatic Sciences, ISSN 0706-652X, E-ISSN 1205-7533, Vol. 67, no 2, 401-416 p.Article in journal (Refereed)
    Abstract [en]

    We hypothesize that size at hatching strongly affects population dynamics of cannibalistic fish species and is a crucial determinant of how populations respond to selective removal of large individuals (harvesting). We use a mechanistic mathematical model to study the relation between hatching size and response to harvesting mortality, using Eurasian perch (Perca fluviatilis) as a model organism. We show how hatching size determines dynamics through its effect on the relative strength of cannibalistic mortality and resource competition as mechanisms of population regulation. In populations with intermediate and large hatching size, cannibalistic mortality is an important determinant of population dynamics. and harvesting destabilizes population dynamics. When hatching size is small, population stability is less sensitive to this type of harvesting. Populations hatching at small size are regulated by competition, and harvesting large individuals affects such populations less. Harvesting can also induce the growth of very large individuals, absent in unharvested populations. Our results show that harvesting in cannibalistic lake fish populations can strongly alter Population dynamics in ways that can only be anticipated on the basis of mechanistic knowledge about how populations are regulated.

  • 37.
    Åhlén, Emma
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Byström, Pär
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Korsman, Tom
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Persson, Lennart
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Reinikainen, Marko
    Tvärminne Zoological Station, Hanko, Finland.
    Planktivore population dynamics affect body size characteristics of Bosmina: evidence from sediment archive and contemporary lake samplesManuscript (preprint) (Other academic)
    Abstract [en]

    Planktivorous fish affect the species composition, morphology and size of their zooplankton prey species by size selective predation. Microfossils of cladocerans are preserved in the lake sediment and hence cladoceran fossil characteristics may be used to reconstruct historical variation of planktivory in lakes. In lakes dominated by fish that are not obligate planktivores (e.g. perch, Perca fluviatilis), the individual size determines to large extent the type of resources consumed. Therefore the size distribution and density of such fish populations determine overall planktivory impact in these lakes.In a Northern Swedish lake over a 9-year period, we compared the carapace length and mucro length of the cladoceran Bosmina spp. from the contemporary samples with the sediment archive. We estimated the temporal variation in overall planktivory pressure on Bosmina by calculating a population planktivore capacity (PPC) measure on zooplankton using the population density and size structure of the perch population together with size dependent attack rate functions on Bosmina.Our results show that temporal changes in body size characteristics of Bosmina in the contemporary and fossil remains were strongly correlated. Contemporary lake samples and fossil remains of Bosmina showed similar responses in body size characteristics to changes in estimated PPC. Initially, when PPC was low in the lake, both size of carapace and mucro were large. As PPC increased due to strong recruitment of perch during the middle of the study period both carapace and mucro size were small, to increase again towards the end of the study when PPC decreased again. Small perch, mainly young-of-the-year (YOY) perch contribution to PPC was high, more than 80% of to the total PPC in most years. This suggests that the contribution of the smallest size classes of fish to PPC can be high and needs to be taken into account when trying to relate changes in zooplankton community characteristics to variation in planktivore densities.The similar response in body size characteristics of Bosmina in contemporary and sediment samples to changes in planktivory pressure strongly suggests the body size characteristics of Bosmina microfossils, i.e. the carapace and mucro length can be used to reconstruct historical changes in planktivory in lakes.

  • 38.
    Åhlén, Emma
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Byström, Pär
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Korsman, Tom
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Persson, Lennart
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Reinikainen, Marko
    Tvärminne Zoological Station, Hanko, Finland.
    Relationships between planktivore community capacity (PCC) and cladoceran microfossils in northern Swedish lakes2011In: Fundamental and Applied Limnology, ISSN 1863-9135, Vol. 178, no 4, 315-324 p.Article in journal (Refereed)
    Abstract [en]

    Planktivorous fish are known to affect the zooplankton community both in terms of species composition and species specific morphological traits. Remains of cladocerans are deposited as microfossils in lake sediments, and the microfossil assembly hence reflects the historical impact of the planktivore community in the lake. The microfossils of cladocerans can therefore be used to reconstruct historical changes in the planktivore fish community in lakes. Catch per unit effort in numbers (CPUEn) and weight (CPUEw) have previously been used as proxies for planktivory. Although these standard measurements are useful in lakes dominated by obligate planktivorous fish, they have limits in their predictive power, particularly in lakes dominated by fish that are not planktivorous throughout their entire lifespan. In this study, we suggest a novel way of estimating the extent of planktivory in lakes, the Planktivore Community Capacity (PCC). PCC takes into account the size and species specific foraging efficiency of fish on zooplankton which gives a more accurate estimate of the intensity of planktivory, especially in lakes dominated by fish that undergo ontogenetic niche shifts from zooplankton to other prey as they grow. Such fish include, for instance, perch (Perca fluviatilis) and Arctic char (Salvelinus alpinus). To analyze the relationship between surface sediment cladoceran remains and planktivory intensity, 39 lakes were sampled regarding the fish community and microfossil assembly. We focused on Bosmina, which is a dominant zooplankton genus in the study area. Bosmina is well preserved in the sediment, and also known to exhibit changes in density and morphology depending on the planktivore predation pressure. We analyzed both the density of two Bosmina species in the sediment and morphological traits in relation to estimates of planktivory intensities. Among the variables measured, morphological traits and relationship between Bosmina longispina and Bosmina longirostris were highly correlated to PCC. PCC had a higher explanatory power than both CPUEn and CPUEw for observed patterns in microfossil characteristics in lakes. We suggest that estimates of Planktivore Community Capacity (PCC) is a powerful approach for reconstructing historical changes in planktivory in lakes.

  • 39.
    Åhlén, Emma
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Byström, Pär
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Korsman, Tom
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Persson, Lennart
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Reinikainen, Marko
    Tvärminne Zoological Station, Hanko, Finland.
    Remains of Bosmina in sediments reflects historical changes in fish populations in a northern Swedish lakeManuscript (preprint) (Other academic)
    Abstract [en]

    Based on morphological measurements on Bosmina in a sediment core from a boreal lake we estimated 60 years back in time historical changes in Planktivore Community Capacity (PCC), a recent derived approach to estimate past planktivore pressure in lakes. We then validated the PCC approach with available information on changes in the lake fish community based on historical knowledge and more recent fish population studies in the lake. Based on available data on fish density, size structure and size dependent attack rate functions on zooplankton we calculated a measure of planktivore pressure in the lake, the Planktivore Population Capacity (PPC). The reconstructed PCC development over the time from Bosmina remains in the sediment core correlated well with PPC estimates (r2 = 0.89 p<0.05) as well as qualitatively with historical information on the development of fish community in the lake. The results from our study suggest that the derived PCC function based on morphological measurements on Bosmina remains in sediments can successfully be used to track historical changes in planktivore communities in lakes.

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