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Sökning: WFRF:(Persson Anders) > Brönmark Christer

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1.
  • Hansson, Lars-Anders, et al. (författare)
  • Food-chain length alters community responses to global change in aquatic systems
  • 2013
  • Ingår i: Nature Climate Change. - Nature Publishing Group. - 1758-678X. ; 3:3, s. 228-233
  • Tidskriftsartikel (refereegranskat)abstract
    • Synergies between large-scale environmental changes, such as climate change(1) and increased humic content (brownification)(2), will have a considerable impact on future aquatic ecosystems. On the basis of modelling, monitoring and experimental data, we demonstrate that community responses to global change are determined by food-chain length and that the top trophic level, and every second level below, will benefit from climate change, whereas the levels in between will suffer. Hence, phytoplankton, and thereby algal blooms, will benefit from climate change in three-, but not in two-trophic-level systems. Moreover, we show that both phytoplankton (resource) and zooplankton (consumer) advance their spring peak abundances similarly in response to a 3 degrees C temperature increase; that is, there is no support for a consumer/resource mismatch in a future climate scenario. However, in contrast to other taxa, cyanobacteria-known as toxin-producing nuisance phytoplankton(3)-benefit from a higher temperature and humic content irrespective of the food-chain composition. Our results are mirrored in natural ecosystems. By mechanistically merging present food-chain theory with large-scale environmental and climate changes, we provide a powerful framework for predicting and understanding future aquatic ecosystems and their provision of ecosystem services and water resources.
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2.
  • Hansson, Lars-Anders, et al. (författare)
  • Consumption patterns, complexity and enrichment in aquatic food chains
  • 1998
  • Ingår i: Proceedings of the Royal Society, London, B. - Royal Society Publishing. - 1471-2954 (Online) .- 0962-8452 (Print). ; 265:1399, s. 901-906
  • Tidskriftsartikel (refereegranskat)abstract
    • The interactions between consumers and prey, and their impact on biomass distribution among trophic levels, are central issues in both empirical and theoretical ecology. In a long-term experiment, where all organisms, including the top predator, were allowed to respond to environmental conditions by reproduction, we tested predictions from `prey-dependent' and `ratio-dependent' models. Prey-dependent models made correct predictions only in the presence of strong interactors in simple food chains, but failed to predict patterns in more complex situations. Processes such as omnivory, consumer excretion, and unsuitable prey-size windows (invulnerable prey) increased the complexity and created patterns resembling ratio-dependent consumption. However, whereas the prey-dependent patterns were created by the mechanisms predicted by the model, ratio-dependent patterns were not, suggesting that they may be right for the wrong reason'. We show here that despite the enormous complexity of ecosystems, it is possible to identify and disentangle mechanisms responsible for observed patterns in community structure, as well as in biomass development of organisms ranging in size from bacteria to fish.
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3.
  • Persson, Anders, et al. (författare)
  • Effects of enrichment on simple aquatic food webs
  • 2001
  • Ingår i: American Naturalist. - University of Chicago Press. - 0003-0147. ; 157:6, s. 654-669
  • Tidskriftsartikel (refereegranskat)abstract
    • Simple models, based on Lotka-Volterra types of interactions between predator and prey, predict that enrichment will have a destabilizing effect on populations and that equilibrium population densities will change at the top trophic level and every second level below. We experimentally tested these predictions in three aquatic food web configurations subjected to either high or low nutrient additions. The results were structured by viewing the systems as either food chains or webs and showed that trophic level biomass increased with enrichment, which contradicts food chain theory. However, within each trophic level, food web configuration affected the extent to which different functional groups responded to enrichment. By dividing trophic levels into functional groups, based on vulnerability to consumption, we were able to identify significant effects that were obscured when systems were viewed as food chains. The results support the prediction that invulnerable prey may stabilize trophic-level dynamics by replacing other, more vulnerable prey. Furthermore, the vulnerable prey, such as Daphnia and edible algae, responded as predicted by the paradox of enrichment hypothesis; that is, variability in population density increased with enrichment. Hence, by describing ecosystems as a matrix of food web interactions, and by recognizing the interplay between interspecific competition and predation, a more complete description of the ecosystem function was obtained compared to when species were placed into distinct trophic levels.
4.
  • Hallgren, Per, et al. (författare)
  • Synthetic estrogen directly affects fish biomass and may indirectly disrupt aquatic food webs
  • 2014
  • Ingår i: Environmental toxicology and chemistry / SETAC. - Wiley-Blackwell / Jossey Bass, Ed. & Pub.. - 1552-8618 .- 0730-7268. ; 33:4, s. 930-936
  • Tidskriftsartikel (refereegranskat)abstract
    • Endocrine-disrupting chemicals are known to alter the fitness of individual organisms via changes in growth, behavior, and reproduction. It is largely unknown, however, whether these effects cascade through the food web and indirectly affect other, less sensitive organisms. The authors present results from a mesocosm experiment whereby the effects of the synthetic estrogen 17α-ethinylestradiol (EE2) were quantified in pelagic communities. Treatment with EE2 at a concentration of 28 ng/L had no large effects on the pelagic communities composed only of phytoplankton and zooplankton. In communities where planktivorous roach (Rutilus rutilus) were also present, however, EE2 caused a significant reduction in fish biomass. Moreover, zooplankton biomass was higher in the EE2 treatments, suggesting that zooplankton may have been released from fish predation. Hence, the direct effect of EE2 on roach may have cascaded down the food web to produce positive indirect effects on zooplankton. This result was supported in complementary foraging experiments with roach, showing reduced foraging performance after exposure to EE2. Despite the observed negative effect of EE2 on roach and the positive indirect effect on zooplankton, these effects did not cascade to phytoplankton, possibly because only copepods, but not cladocerans—the major grazers in these systems—were released from fish predation. The authors conclude that the known reproductive impairment in fish by EE2 in combination with the disturbed foraging performance observed in the present study may be a disadvantage to fish that may result in increasing abundance or biomass of prey such as zooplankton. Hence, EE2 may have consequences for both the structure and function of freshwater communities.
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5.
  • Kritzberg, Emma, et al. (författare)
  • Warming and browning of lakes: consequences for pelagic carbon metabolism and sediment delivery
  • 2014
  • Ingår i: Freshwater Biology. - Wiley-Blackwell Publishing. - 0046-5070. ; 59:2, s. 325-336
  • Tidskriftsartikel (refereegranskat)abstract
    • 1. Thousands of lakes in the Northern Hemisphere are experiencing a continuous increase in water temperature and colour. While increasing temperature is an effect of climate change, several factors are suggested to drive the increasing water colour, including climate change, altered land use and reversed acidification. 2. In this mesocosm study, we study the effects on pelagic production and sedimentation of organic carbon from a 3 degrees C increase in temperature, a doubling of water colour and a combination of increased temperature and water colour. These manipulations correspond to the predicted development in water colour and temperature in northern temperate systems within the life time of the next generation. 3. The water and plankton communities in the mesocosms were taken from an oligohumic and mesotrophic lake, and the increase in water colour was achieved by the additions of water from a humic lake. The experiment ran from early March to late October. 4. In accordance with our predictions and previous cross-system analyses, net carbon production (NCP) and organic carbon sedimentation decreased in response to increasing water colour. 5. At odds with current theory, NCP and sedimentation increased in heated treatments, as not only respiration but also gross production increased in response to temperature. There were no synergistic effects between warming and browning. 6. These results imply that warming may enhance pelagic delivery of organic carbon to sediments. This could potentially offset a reduction in burial efficiency of organic carbon, which has been projected based on a positive relationship between carbon mineralisation in sediments and temperature.
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6.
  • Nicolle, Alice, et al. (författare)
  • Predicted warming and browning affect timing and magnitude of plankton phenological events in lakes: a mesocosm study
  • 2012
  • Ingår i: Freshwater Biology. - Wiley-Blackwell. - 0046-5070. ; 57:4, s. 684-695
  • Tidskriftsartikel (refereegranskat)abstract
    • 1. Aquatic ecosystems in Northern Europe are expected to face increases in temperature and water colour (TB) in future. While effects of these factors have been studied separately, it is unknown whether and how a combination of them might affect phenological events and trophic interactions. 2. In a mesocosm study, we combined both factors to create conditions expected to arise during the coming century. We focused on quantifying effects on timing and magnitude of plankton spring phenological events and identifying possible mismatches between resources (phytoplankton) and consumers (zooplankton). 3. We found that the increases in TB had important effects on timing and abundance of different plankton groups. While increased temperature led to an earlier peak in phytoplankton and zooplankton and a change in the relative timing of different zooplankton groups, increased water colour reduced chlorophyll-a concentrations. 4. Increased TB together benefitted cladocerans and calanoid copepods and led to stronger top-down control of algae by zooplankton. There was no sign of a mismatch between primary producers and grazers as reported from other studies. 5. Our results point towards an earlier onset of plankton spring growth in shallow lakes in future with a stronger top-down control of phytoplankton by zooplankton grazers.
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7.
  • Nilsson, Anders, et al. (författare)
  • Behavioral interference and facilitation in the foraging cycle shape the functional response
  • 2007
  • Ingår i: Behavioral Ecology. - Oxford University Press. - 1045-2249 .- 1465-7279. ; 18:2, s. 354-357
  • Tidskriftsartikel (refereegranskat)abstract
    • Individual forager behaviors should affect per capita intake rates and thereby population and consumer-resource properties. We consider and incorporate conspecific facilitation and interference during the separate foraging-cycle stages in a functional response model that links individual behavioral interactions with consumer-resource processes. Our analyses suggest that failing to properly consider and include all effects of behavioral interactions on foraging-cycle stage performances may either over- or underestimate effects of interactions on the shape of both functional responses and predator zero-growth isoclines. Incorporation of prey- and predator-dependent interactions among foragers in the model produces predator isoclines with potentials for highly complex consumer-resource dynamics. Facilitation and interference during the foraging cycle are therefore suggested as potent behavioral mechanisms to cause patterns of community dynamics. We emphasize that correct estimations of interaction-mediated foraging-cycle efficiencies should be considered in empirical and theoretical attempts to further our understanding of the mechanistic link between social behaviors and higher order processes.
8.
  • Ranaker, Lynn, et al. (författare)
  • Piscivore-Prey Fish Interactions:
  • 2014
  • Ingår i: PloS one. - PLoS. - 1932-6203. ; 9:11, s. e102002
  • Tidskriftsartikel (refereegranskat)abstract
    • Environmental change may affect predator-prey interactions in lakes through deterioration of visual conditions affecting foraging success of visually oriented predators. Environmental change in lakes includes an increase in humic matter causing browner water and reduced visibility, affecting the behavioural performance of both piscivores and prey. We studied diurnal patterns of prey selection in piscivorous pikeperch (Sander lucioperca) in both field and laboratory investigations. In the field we estimated prey selectivity and prey availability during day and night in a clear and a brown water lake. Further, prey selectivity during day and night conditions was studied in the laboratory where we manipulated optical conditions (humic matter content) of the water. Here, we also studied the behaviours of piscivores and prey, focusing on foraging-cycle stages such as number of interests and attacks by the pikeperch as well as the escape distance of the prey fish species. Analyses of gut contents from the field study showed that pikeperch selected perch (Perca fluviatilis) over roach (Rutilus rutilus) prey in both lakes during the day, but changed selectivity towards roach in both lakes at night. These results were corroborated in the selectivity experiments along a brown-water gradient in day and night light conditions. However, a change in selectivity from perch to roach was observed when the optical condition was heavily degraded, from either brown-stained water or light intensity. At longer visual ranges, roach initiated escape at distances greater than pikeperch attack distances, whereas perch stayed inactive making pikeperch approach and attack at the closest range possible. Roach anti-predatory behaviour decreased in deteriorated visual conditions, altering selectivity patterns. Our results highlight the importance of investigating both predator and prey responses to visibility conditions in order to understand the effects of degrading optical conditions on piscivore-prey interaction strength and thereby ecosystem responses to brownification of waters.
9.
  • Persson, Anders, et al. (författare)
  • Foraging capacities and effects of competitive release on ontogenetic diet shift in bream, Abramis brama
  • 2002
  • Ingår i: Oikos. - Blackwell Publishing. - 1600-0706 .- 0030-1299. ; 97:2, s. 271-281
  • Tidskriftsartikel (refereegranskat)abstract
    • Bream Abramis brama) undergo ontogenetic diet shift from zooplankton to benthic macroinvertebrates, but the switching size may be highly variable. To unravel under what conditions bream are pelagic versus benthic foragers, we experimentally determined size-dependent foraging capacities on three prey types from the planktivory and benthivory niche: zooplankton, visible and buried macroinvertebrates. From these data we derived predictions of size-dependent diet preferences from estimates of prey value and competitive ability, and tested these predictions on diet data from the field. Planktivorous foraging capacity described a hump-shaped relationship with bream length that peaked for small bream of 67 mm total length. Benthivory capacity increased with increasing bream size, irrespective if benthic prey were visible on the sediment surface or buried in the sediment. From the experimental data and relationships of metabolic demand we calculated minimum resource requirement for maintenance (MRR) for each of the prey categories used in experiments. MRR increased with bream size for both zooplankton and visible chironomids, but decreased with bream size for buried chironomids, suggesting that intermediate sized bream (120-300 mm) may be competitively sandwiched between small and large bream that are more competitive planktivores and benthivores, respectively. Prey value estimates and competitive abilities qualitatively predicted diet shift in a bream population being released from competition. Competitive release did not change the diet of the largest size-class feeding on an optimal diet of benthic invertebrates both before and after competitive release. However, profound diet shifts towards benthic macro invertebrates were recorded for intermediate size-classes that fed on a suboptimal diet prior to competitive release. Thus, laboratory estimates of size-dependent foraging capacity of bream in planktivorous and benthivorous feeding niches provided useful information on size-specific competitive ability, and successfully predicted diet preference in the field.
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10.
  • Persson, Anders, et al. (författare)
  • Foraging capacity and resource synchronization in an ontogenetic diet switcher, pikeperch (Stizostedion lucioperca)
  • 2002
  • Ingår i: Ecology. - Ecological Society of America. - 0012-9658. ; 83:11, s. 3014-3022
  • Tidskriftsartikel (refereegranskat)abstract
    • Species undergoing ontogenetic diet shifts face a risk of resource competition that delays transitions between feeding stages. Such ontogenetic bottlenecks are common in piscivorous fish because competition with future prey may retard growth and prevent a size advantage. In pikeperch (Stizostedion lucioperca), year class strength of 0+ cohorts is highly variable and positively related to early onset of piscivory. To identify the causes of this pattern, we experimentally quantified size-dependent planktivorous and piscivorous foraging capacity and incorporated the data into a growth model. For any given prey type and size, foraging capacity described a hump-shaped relationship with predator size. Foraging capacity on daphnids peaked at a pikeperch length of 66 mm, suggesting a narrow scope of planktivory. The highest capacity in the piscivorous niche was reached at a predator-to-prey length ratio of 5, where the ratio was an integrated measure of predator size over several prey sizes. With the growth model, we derived size distributions of 0+ cohorts as functions of resource levels. Simulations revealed two major determinants for the year class strength of pikeperch. First, discontinuous availability of prey sizes counteracted switching to piscivory within the first growing season. This was accentuated by prey fish growth, which caused the planktivory and piscivory niches to separate over time and limited the time window when diet shift was possible. Second, the hump-shaped relationship between size and foraging capacity resulted in growth reduction when growing out of the planktivorous niche. Switching to piscivory in our model occurred along a perpendicular relationship between fish prey and zooplankton density. Zooplankton density determined whether pikeperch reached a size advantage over prey, and fish prey density affected whether the foraging return of piscivory was higher than planktivory. Individuals not reaching a size advantage over prey and failing to become piscivorous were stunted at a size when consumption balanced metabolic requirements. Piscivorous individuals, however, continued to grow fast throughout the season by feeding on the wave of the prey cohort. Our results highlight the importance for predators that shift diet to be synchronized with fluctuations in resource availability, such as the pulses of new cohorts of prey fish.
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