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Sökning: WFRF:(Peter Eklöv)

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1.
  • Andersson, Matilda L., et al. (författare)
  • Chasing away accurate results : exhaustive chase protocols underestimate maximum metabolic rate estimates in European perch Perca fluviatilis
  • 2020
  • Ingår i: Journal of Fish Biology. - : Wiley. - 0022-1112 .- 1095-8649. ; 97:6, s. 1644-1650
  • Tidskriftsartikel (refereegranskat)abstract
    • Metabolic rates are one of many measures that are used to explain species' response to environmental change. Static respirometry is used to calculate the standard metabolic rate (SMR) of fish, and when combined with exhaustive chase protocols it can be used to measure maximum metabolic rate (MMR) and aerobic scope (AS) as well. While these methods have been tested in comparison to swim tunnels and chambers with circular currents, they have not been tested in comparison with a no‐chase control. We used a repeated‐measures design to compare estimates of SMR, MMR and AS in European perch Perca fluviatilis following three protocols: (a) a no‐chase control; (b) a 3‐min exhaustive chase; and (c) a 3‐min exhaustive chase followed by 1‐min air exposure. We found that, contrary to expectations, exhaustive chase protocols underestimate MMR and AS at 18°C, compared to the no‐chase control. This suggests that metabolic rates of other species with similar locomotorty modes or lifestyles could be similarly underestimated using chase protocols. These underestimates have implications for studies examining metabolic performance and responses to climate change scenarios. To prevent underestimates, future experiments measuring metabolic rates should include a pilot with a no‐chase control or, when appropriate, an adjusted methodology in which trials end with the exhaustive chase instead of beginning with it.
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2.
  • Andersson, Matilda L. (författare)
  • Fish population responses to climate change : Causes and consequences
  • 2021
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Lake environments are heterogeneous, and animals show a variety of adaptations to deal with this heterogeneity. Fish often show intraspecific variation in diet, metabolism, and behavior, corresponding to their habitat use. Studies on climate change often ignore this heterogeneity and its importance in determining population-level responses to climate change. This thesis can be broken into two interacting pieces. First, my goal was to assess how water color and temperature changes impact the size, number, and distribution of a common predator, Eurasian perch (Perca fluviatilis), in Swedish lakes. Second, I aimed to examine whether metabolism and resource use differed between lake habitats, corresponding with documented patterns of polymorphism and whether diet differences were maintained along a thermal and water color gradient. By combining the information gleaned from these studies, the overarching goal of my thesis is to better understand how climate change will impact fish populations and how intraspecific variance in these responses will impact ecosystem functioning. I found that warming and browning will likely decrease fish biomass but via different mechanisms. Warming reduces average fish size through its impact on metabolism and energy requirements. Browning decreases fish abundance likely due to its negative effects on resource abundance, increasing mortality, and decreasing reproductive effort. Though warming decreases biomass at the lake level, pelagic perch abundance increases. I found that these pelagic perch have higher metabolic rates and, especially in darker lakes, rely heavily on pelagic resources. As more fish shift into the pelagic habitat, this will increase top-down pressure on pelagic resources and decrease energy transfer from littoral to pelagic habitats altering energy flow within lakes. Variation in metabolic phenotype across habitats, combined with the positive scaling of metabolic rates with temperature, will likely determine which fish can persist under climate change scenarios. Studies that measure this variation rely heavily on respirometry to measure fish metabolism. I found that current respirometry methods underestimate maximum metabolic rate and suggest an updated method to improve the accuracy of future studies. Overall, I conclude that habitats should be examined separately to better understand population-level responses to climate change. Perch caught in different habitats have different energy requirements and respond differently to warming and browning. These differences will affect the distribution of top-down pressure and habitat coupling within lake ecosystems, with implications for broader ecosystem functioning in the future. 
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3.
  • Andersson, Matilda L., et al. (författare)
  • Habitat coupling is modified by dissolved organic carbon but not temperature in lake ecosystems
  • Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
    • Generalist predators play an essential role in lake ecosystems by linking spatially distinct habitats, a process known as habitat coupling. By eating a wide array of resources and moving between littoral and pelagic habitats, they link food webs and provide critical habitat stability. As climate change is expected to affect ecosystem stability, our attention should focus on how habitat coupling in these predator-stabilized systems is altered by climate change.Expected climate change effects in boreal regions are increases in temperature and dissolved organic carbon (DOC) concentrations. Therefore, we used stable isotopes and a space-for-time approach to examine the impact of DOC and temperature on resource use in a generalist predator, European perch (Perca fluviatilis), in 17 lakes in Sweden and Germany. We found that the impact of DOC on habitat coupling depended on fish ecotype, while both ecotypes showed increases in pelagic resource use, this will increase coupling by littoral fish, while decreasing coupling by pelagic fish. Though we found no direct effect of temperature on resource use, we did find that fish size, which decreases with warming, has an impact. We show that in the future, as fish size decreases and DOC increases, generalist predators will couple habitats less and have a more narrow dietary niche width. This shows that while perch will respond flexibly to changes in resource availability, stability may decrease in the process. 
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4.
  • Andersson, Matilda L., et al. (författare)
  • Habitat specific impacts of warming and browning on a generalist freshwater predator
  • Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
    • Mobile generalist predators are important components of community food webs because they can forage over a large spatial range and provide links that mediate ecosystem responses to climate change. However, many species show intraspecific variation in habitat and resource use. By evaluating the effects of increased temperature and water color on a predator fish living in two contiguous habitats, we can better understand how climate change effects can be mediated by specific ecotypes’ responses, and the implications for future ecosystem functioning.Using a space for time approach, our study examines the impact of increased temperature and water color of inland waters on European perch (Perca fluviatilis) populations, differentiating between the effects on perch inhabiting littoral and pelagic habitats. We found that littoral perch abundance decreased with increasing water color, likely as a result of decreased fecundity and prey availability. Average littoral perch size decreased with increasing temperatures reinforcing the negative effects of browning in reducing littoral perch biomass. In contrast, the biomass of pelagic perch increased with increasing temperature due to increased abundance and was not impacted by water color. Combined, this resulted in a shift towards a higher proportion of the perch population occupying the pelagic habitat in warmer lakes. These shifts in size and abundance at the lake level and between habitats are likely to impact ecosystem functioning and stability as the climate continues to change and will also affect fisheries and recreation. 
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5.
  • Andersson, Matilda L., et al. (författare)
  • The interaction between metabolic rate, habitat choice, and resource use in a polymorphic freshwater species
  • 2022
  • Ingår i: Ecology and Evolution. - : John Wiley & Sons. - 2045-7758. ; 12:8
  • Tidskriftsartikel (refereegranskat)abstract
    • 1.      Resource polymorphism is common across taxa and can result in alternate ecotypes with specific morphologies, feeding modes, and behaviours that increase performance in a specific habitat. This can result in high intraspecific variation in the expression of specific traits and the extent to which these traits are correlated within a single population. Although metabolic rate influences resource acquisition and the overall pace of life of individuals it is not clear how metabolic rate interact with the larger suite of traits to ultimately determine individual fitness.2.      We examined the relationship between metabolic rates and the major differences (habitat use, morphology, and resource use) between littoral and pelagic ecotypes of European perch (Perca fluviatilis) from a single lake in Central Sweden.3.      Standard metabolic rate (SMR) was significantly higher in pelagic perch but did not correlate with resource use or morphology. Maximum metabolic rate (MMR) was not correlated with any of our explanatory variables or with SMR. Aerobic scope (AS) showed the same pattern as SMR, differing across habitats, but contrary to expectations was lower in pelagic perch.4.      This study helps to establish a framework for future experiments further exploring the drivers of intraspecific differences in metabolism. In addition, since metabolic rates scale with temperature and determine predator energy requirements, our observed differences in SMR across habitats will help determine ecotype-specific vulnerabilities to climate change and differences in top-down predation pressure across habitats.
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6.
  • Bartels, Pia, et al. (författare)
  • Dissolved Organic Carbon Reduces Habitat Coupling by Top Predators in Lake Ecosystems
  • 2016
  • Ingår i: Ecosystems (New York. Print). - : Springer Science and Business Media LLC. - 1432-9840 .- 1435-0629. ; 19, s. 955-967
  • Tidskriftsartikel (refereegranskat)abstract
    • Increasing input of terrestrial dissolved organic carbon (DOC) has been identified as a widespread environmental phenomenon in many aquatic ecosystems. Terrestrial DOC influences basal trophic levels: it can subsidize pelagic bacterial production and impede benthic primary production via light attenuation. However, little is known about the impacts of elevated DOC concentrations on higher trophic levels, especially on top consumers. Here, we used Eurasian perch (Perca fluviatilis) to investigate the effects of increasing DOC concentrations on top predator populations. We applied stable isotope analysis and geometric morphometrics to estimate long-term resource and habitat utilization of perch. Habitat coupling, the ability to exploit littoral and pelagic resources, strongly decreased with increasing DOC concentrations due to a shift toward feeding predominantly on pelagic resources. Simultaneously, resource use and body morphology became increasingly alike for littoral and pelagic perch populations with increasing DOC, suggesting more intense competition in lakes with high DOC. Eye size of perch increased with increasing DOC concentrations, likely as a result of deteriorating visual conditions, suggesting a sensory response to environmental change. Increasing input of DOC to aquatic ecosystems is a common result of environmental change and might affect top predator populations in multiple and complex ways.
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7.
  • Bartels, Pia (författare)
  • Ecology across Boundaries : Food web coupling among and within ecosystems
  • 2011
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Cross-boundary movements of energy and material are ubiquitous. Freshwater ecosystems receive nutrients, dissolved, and particulate organic matter from adjacent terrestrial ecosystems, whereas terrestrial ecosystems mainly receive prey organisms and detritus deposited by physical processes such as floods from freshwater ecosystems. Within lakes, fish are considered as integrators between habitats due to their high mobility, although they often occupy either near-shore littoral or open-water pelagic habitats and develop habitat-specific morphologies. Such intra-population divergence in morphological traits might limit the use of multiple habitats. In this thesis, I first focused on quantity and quality of reciprocal fluxes of particulate organic matter between freshwater and terrestrial ecosystems and responses of recipient consumers. Freshwater ecosystems generally received higher amounts of externally-produced resources than terrestrial ecosystems. Despite this discrepancy, aquatic and terrestrial consumer responses were similar, likely due to the differences in resource quality. Second, I investigated the potential of particulate organic carbon (POC) supporting benthic food webs in lakes; a pathway that has largely been neglected in previous studies. I found that POC can substantially subsidize the benthic food web and that the effects on the benthic food web were transferred to the pelagic habitat, thus emphasizing the importance of benthic pathways for pelagic production. Third, I examined how water transparency can affect intra-population divergence in perch (Perca fluviatilis). I observed that increased water transparency can considerably increase morphological divergence between littoral and pelagic populations likely due to its effects on foraging. Finally, I investigated the effects of such intra-population divergence on littoral-pelagic food web coupling. I found that low morphological divergence corresponded with high overlap in resource use, whereas strong morphological divergence resulted in low overlap in resource use. Here littoral populations mainly utilized littoral resources and pelagic populations primarily utilized pelagic resources, indicating that habitat coupling might be strongly limited when intra-population divergence is high. In conclusion, although different ecosystems seem separated by distinct physical boundaries, these boundaries are often crossed. However, the development of habitat-specific adaptive traits might limit movement between apparently contiguous habitats.
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8.
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9.
  • Bartels, Pia, et al. (författare)
  • Reciprocal subsidies between freshwater and terrestrial ecosystems structure consumer resource dynamics
  • 2012
  • Ingår i: Ecology. - : Wiley. - 0012-9658 .- 1939-9170. ; 93:5, s. 1173-1182
  • Tidskriftsartikel (refereegranskat)abstract
    • Cross-ecosystem movements of material and energy, particularly reciprocal resource fluxes across the freshwater-land interface, have received major attention. Freshwater ecosystems may receive higher amounts of subsidies (i.e., resources produced outside the focal ecosystem) than terrestrial ecosystems, potentially leading to increased secondary production in freshwaters. Here we used a meta-analytic approach to quantify the magnitude and direction of subsidy inputs across the freshwater-land interface and to determine subsequent responses in recipient animals. Terrestrial and freshwater ecosystems differed in the magnitude of subsidies they received, with aquatic ecosystems generally receiving higher subsidies than terrestrial ecosystems. Surprisingly, and despite the large discrepancy in magnitude, the contribution of these subsidies to animal carbon inferred from stable isotope composition did not differ between freshwater and terrestrial ecosystems, likely due to the differences in subsidy quality. The contribution of allochthonous subsidies was highest to primary consumers and predators, suggesting that bottom-up and top-down effects may be affected considerably by the input of allochthonous resources. Future work on subsidies will profit from a food web dynamic approach including indirect trophic interactions and propagating effects.
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10.
  • Bartels, Pia, et al. (författare)
  • Terrestrial subsidies to lake food webs : an experimental approach
  • 2012
  • Ingår i: Oecologia. - New York : Springer. - 0029-8549 .- 1432-1939. ; 168:3, s. 807-818
  • Tidskriftsartikel (refereegranskat)abstract
    • Cross-ecosystem movements of material and energy are ubiquitous. Aquatic ecosystems typically receive material that also includes organic matter from the surrounding catchment. Terrestrial-derived (allochthonous) organic matter can enter aquatic ecosystems in dissolved or particulate form. Several studies have highlighted the importance of dissolved organic carbon to aquatic consumers, but less is known about allochthonous particulate organic carbon (POC). Similarly, most studies showing the effects of allochthonous organic carbon (OC) on aquatic consumers have investigated pelagic habitats; the effects of allochthonous OC on benthic communities are less well studied. Allochthonous inputs might further decrease primary production through light reduction, thereby potentially affecting autotrophic resource availability to consumers. Here, an enclosure experiment was carried out to test the importance of POC input and light availability on the resource use in a benthic food web of a clear-water lake. Corn starch (a C-4 plant) was used as a POC source due to its insoluble nature and its distinct carbon stable isotope value (delta C-13). The starch carbon was closely dispersed over the bottom of the enclosures to study the fate of a POC source exclusively available to sediment biota. The addition of starch carbon resulted in a clear shift in the isotopic signature of surface-dwelling herbivorous and predatory invertebrates. Although the starch carbon was added solely to the sediment surface, the carbon originating from the starch reached zooplankton. We suggest that allochthonous POC can subsidize benthic food webs directly and can be further transferred to pelagic systems, thereby highlighting the importance of benthic pathways for pelagic habitats.
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11.
  • Bartels, Pia, et al. (författare)
  • Water transparency drives intra-population divergence in Eurasian perch (Perca fluviatilis)
  • 2012
  • Ingår i: PLOS ONE. - San Francisco : Public Library of Science (PLoS). - 1932-6203. ; 7:8
  • Tidskriftsartikel (refereegranskat)abstract
    • Trait combinations that lead to a higher efficiency in resource utilization are important drivers of divergent natural selection and adaptive radiation. However, variation in environmental features might constrain foraging in complex ways and therefore impede the exploitation of critical resources. We tested the effect of water transparency on intra-population divergence in morphology of Eurasian perch (Perca fluviatilis) across seven lakes in central Sweden. Morphological divergence between near-shore littoral and open-water pelagic perch substantially increased with increasing water transparency. Reliance on littoral resources increased strongly with increasing water transparency in littoral populations, whereas littoral reliance was not affected by water transparency in pelagic populations. Despite the similar reliance on pelagic resources in pelagic populations along the water transparency gradient, the utilization of particular pelagic prey items differed with variation in water transparency in pelagic populations. Pelagic perch utilized cladocerans in lakes with high water transparency and copepods in lakes with low water transparency. We suggest that under impaired visual conditions low utilization of littoral resources by littoral perch and utilization of evasive copepods by pelagic perch may lead to changes in morphology. Our findings indicate that visual conditions can affect population divergence in predator populations through their effects on resource utilization.
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12.
  • Chaguaceda, Fernando (författare)
  • Bottom-up and top-down regulation of heterogeneous lake food webs
  • 2020
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Food webs are networks of organisms linked by trophic interactions that regulate the responses of ecosystems to environmental change. Such regulation is a result of the effects of resources on the abundance of their consumers (i.e. bottom-up effects) and/or the influence of consumers on the abundance of their resources (i.e. top-down effects). Lake food webs comprise pelagic and benthic production pathways and are largely affected by fluxes of resources from/to adjacent terrestrial ecosystems. These pathways are often coupled by mobile generalist consumers, potentially leading to indirect interactions among prey that arise when sharing a predator. In contrast, consumers can also undergo resource specialization that restricts their ability to couple resources at a given time.In this thesis, I observed that top-down control of predators on benthic and pelagic prey at increasing productivity was highly dependent on apparent mutualism that was driven by switching behaviour of generalist fish. That, in addition to bottom-up responses of benthic pathways at increasing productivity, had important consequences for the fluxes of energy and high quality polyunsaturated fatty acids (PUFAs) to terrestrial systems via insect emergence. I also found that PUFAs were highly regulated over the ontogeny of Eurasian perch (Perca fluviatilis). Mismatches with PUFA composition in prey may in turn affect resource specialization and the timing of ontogenetic diet shifts, altering the role of perch in the food web. Finally, browning, which is a phenomenon affecting many temperate and boreal lakes, did not affect bottom-up and top-down control in open-water lake food webs. Instead, browning affected prey selectivity, probably changing the pathways of energy transfer within the open-water food web. Overall, this thesis demonstrates that predictions of food web responses in lake ecosystems and their exports to adjacent terrestrial systems depend on the coupling of different pathways and subsequent indirect interactions among prey through shared predation. This could not be explained by classic food chain theory, but rather by a framework including resource coupling and resource specialization over the ontogeny of consumers. These observations must not be overlooked when constructing a comprehensive model of food webs across time and space.
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13.
  • Chaguaceda, Fernando, et al. (författare)
  • Chaguaceda et al. (2020) Oecologia dataset
  • 2020
  • Annan publikationabstract
    • Fatty acids (FAs) are key nutrients for fitness which take part in multiple physiological processes over the ontogeny of organisms. Yet, we lack evidence on how FA nutrition mediates life-history trade-offs and ontogenetic niche shifts in natural populations. In a field study, we analyzed ontogenetic changes in the FAs of Eurasian perch (Perca fluviatilis L.), a widespread fish that goes through ontogenetic niche shifts and can have high individual niche specialization. Diet explained most of the variation in the FA composition of perch dorsal muscle over early ontogeny (28%), while the total length explained 23%, suggesting that perch significantly regulated FA composition over early ontogeny. Condition explained 1% of the remaining variation. 18:3n-3 (ALA) and 18:4n-3 (SDA) indicated planktivory; 18:1n-7, benthivory; and 22:6n-3 (DHA), piscivory in perch diet. Conversely, perch regulated long-chained polyunsaturated fatty acids (PUFAs), such as 20:5n-3 (EPA), 20:4n-6 (ARA) and 22:6n-3 (DHA) over ontogeny, emphasizing the role of such FAs in early growth and sexual maturation. Adult perch increasingly retained 16:1n-7 and 18:1n-9 suggesting higher energy storage in older perch. Furthermore, differences in DHA availability in diet correlated with intra-cohort differences in perch growth, potentially hindering the overall use of benthic resources and promoting earlier shifts to piscivory in littoral habitats. Overall, this study indicates that in addition to diet, internal regulation may be more important for FA composition than previously thought. Differences between FA needs and FA availability may lead to life-history trade-offs that affect the ecology of consumers, including their niche
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14.
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15.
  • Chaguaceda, Fernando, et al. (författare)
  • Regulation of fatty acid composition related to ontogenetic changes and niche differentiation of a common aquatic consumer
  • 2020
  • Ingår i: Oecologia. - : Springer Science and Business Media LLC. - 0029-8549 .- 1432-1939. ; 193:2, s. 325-336
  • Tidskriftsartikel (refereegranskat)abstract
    • Fatty acids (FAs) are key nutrients for fitness which take part in multiple physiological processes over the ontogeny of organisms. Yet, we lack evidence on how FA nutrition mediates life-history trade-offs and ontogenetic niche shifts in natural populations. In a field study, we analyzed ontogenetic changes in the FAs of Eurasian perch (Perca fluviatilis L.), a widespread fish that goes through ontogenetic niche shifts and can have high individual niche specialization. Diet explained most of the variation in the FA composition of perch dorsal muscle over early ontogeny (28%), while the total length explained 23%, suggesting that perch significantly regulated FA composition over early ontogeny. Condition explained 1% of the remaining variation. 18:3n-3 (ALA) and 18:4n-3 (SDA) indicated planktivory; 18:1n-7, benthivory; and 22:6n-3 (DHA), piscivory in perch diet. Conversely, perch regulated long-chained polyunsaturated fatty acids (PUFAs), such as 20:5n-3 (EPA), 20:4n-6 (ARA) and 22:6n-3 (DHA) over ontogeny, emphasizing the role of such FAs in early growth and sexual maturation. Adult perch increasingly retained 16:1n-7 and 18:1n-9 suggesting higher energy storage in older perch. Furthermore, differences in DHA availability in diet correlated with intra-cohort differences in perch growth, potentially hindering the overall use of benthic resources and promoting earlier shifts to piscivory in littoral habitats. Overall, this study indicates that in addition to diet, internal regulation may be more important for FA composition than previously thought. Differences between FA needs and FA availability may lead to life-history trade-offs that affect the ecology of consumers, including their niche.
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16.
  • Chaguaceda, Fernando, et al. (författare)
  • Short-term apparent mutualism drives responses of aquatic prey at increasing productivity
  • 2021
  • Ingår i: Journal of Animal Ecology. - : John Wiley & Sons. - 0021-8790 .- 1365-2656. ; 90:4, s. 834-845
  • Tidskriftsartikel (refereegranskat)abstract
    • According to apparent competition theory, sharing a predator should cause indirect interactions among prey that can substantially influence food-web responses to environmental drivers. However, empirical evidence of apparent competition under ongoing environmental change is still scarce. In an 8-week mesocosm experiment, we found that short-term responses of aquatic food webs to increasing productivity were strongly regulated by apparent mutualism between benthic and pelagic prey in the presence of a generalist fish. Following trends in natural systems, increasing productivity in our mesocosms favored the relative abundance of benthic prey. This elicited a shift in fish selectivity from pelagic to benthic prey driven by fish switching behavior which resulted in lower and delayed top-down control on pelagic prey. Our results highlight that apparent competition theory may explain food-web responses across environmental gradients, whereby resulting prey dynamics and stability may highly depend on the foraging behavior exhibited by generalist predators.
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17.
  • Chaguaceda, Fernando, et al. (författare)
  • Supportive data for "Short-term apparent mutualism drives responses of aquatic prey to increasing productivity", Chaguaceda et al.
  • 2020
  • Annan publikationabstract
    • This dataset contains both biological variables (phytoplankton, periphyton, zooplankton, Chironomidae emergence) and physico-chemical variables (temperature, dissolved oxygen, pH, turbidity) of an aquatic mesocosm experiment that gradually manipulated nutrient additions (10 nutrient steps, 20 – 1000 µg L -1 total P (TP) and 0.45 – 11.3 mg L -1 total N (TN)) and also manipulated the presence or absence of generalist fish (Crucian carp, Carassius carassius), making a total of 10*2=20 mesocosms.Crucian carp feed both on benthic prey (Chironomidae) and on pelagic prey (Cladocera). Based on that, this experiment aimed to test the indirect interactions between Chironomidae and Cladocera prey due to shared predation, and how these interactions changed in response to nutrient additions through changes in benthic and pelagic food-web pathways. In the dataset there are five different sheets:Sheet number 1 shows the summary values of all the variables after the fish were added. Most variables are shown as mean values over a 7-week experimental period (after fish addition). The  other sheets show the time-series of food-web variables (Phytoplankton Chla, periphyton biomass, Chironomidae emergence and Cladocera abundance), where the week refers to week relative to fish addition (week 0 is the first week after fish addition).
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18.
  • Diehl, S., et al. (författare)
  • EFFECTS OF PISCIVORE-MEDIATED HABITAT USE ON RESOURCES, DIET, AND GROWTH OF PERCH
  • 1995
  • Ingår i: Ecology. - UMEA UNIV,DEPT ANIM ECOL,S-90187 UMEA,SWEDEN. : Wiley. - 0012-9658 .- 1939-9170. ; 76:6, s. 1712-1726
  • Tidskriftsartikel (refereegranskat)abstract
    • We investigated experimentally how presence or absence of different piscivores influenced habitat use, diet, and individual growth of two size classes of juvenile perch (Perca fluviatilis) and abundances of juvenile perch resources in different habitats. Pond enclosures encompassed 3 X 6 m of dense vegetation and 9 X 6 m of open habitat, and were stocked with 75 young-of-year and 30 1-yr-old perch and with either three piscivorous perch, three northern pike (Esox lucius), or no piscivores. Northern pike were both larger and possessed a larger gape than piscivorous perch. To isolate behavioral responses of juvenile perch to piscivores, we replaced consumed young-of-year perch. Prey fish mortality was lowest without piscivores and highest with northern pike. Young-of-year perch increased their use of vegetation in the presence of both piscivores, whereas 1-yr-old perch increased their use of vegetation only with northern pike. For both age classes of prey fish, increased use of the vegetation led to reduced individual growth, owing to two complementary mechanisms. First, the physical complexity of submerged macrophytes likely interfered with the benthic feeding of perch, Second, increased use of the (relatively small) vegetated habitat increased the mean density experienced by prey fish. Piscivore-induced changes of prey fish densities in the two habitats had substantial effects on the biomass of prey fish resources in the open habitat, but only minor effects in the vegetation. Sialis lutaria, the major predatory macroinvertebrate (approximate to 50% of total macroinvertebrate biomass in the open habitat), and total predatory macroinvertebrates were positively affected by piscivores in the open habitat, but not in the vegetation. Chironomids (<3% of total macroinvertebrate biomass in the vegetation) and the sizes of nonpredatory macroinvertebrates were negatively affected by piscivores in the vegetation, but not in the open habitat. Biomass of nonpredatory macroinvertebrates, Cladocera, and Copepoda did not differ among treatments in either habitat. From our review of field experiments, vulnerable prey fish always change their habitat use in the presence of piscivores. Behaviorally mediated indirect effects of piscivores on individual growth rates and prey fish resources were just as frequently observed as direct effects of piscivores on prey fish survival.
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19.
  • Eklöv Ahlander, Gunilla, et al. (författare)
  • The construction of status in the auditor–audit committee relationship
  • 2023
  • Ingår i: Auditing transformation : Regulation, Digitalisation and Sustainability - Regulation, Digitalisation and Sustainability. - 9781003411390 - 9781032533032 ; :50, s. 46-68
  • Bokkapitel (refereegranskat)abstract
    • This chapter investigates the construction of status in the relationship between the auditor and the audit committee. Such a study is merited considering that regulation as a driver of corporate governance has been designed towards a regulatory concern with lax audit practice, where the audit committee was presented as a solution. This is, however, a problem not manifested in the Swedish context. The driver was instead connected to the need for companies to follow suit with an Anglo-Saxon regulatory development. The study is informed by interviews with audit committee members and external auditors in large, listed companies and contributes novel insights to the understanding of the transformation of the role of the auditor due to the regulatory driver represented by the audit committees. The findings show a rather paradoxical development where the auditors increase their status through direct access to the board of directors, while also decreasing their status by being reduced to a supplier, among other suppliers of trust and comfort to the directors. The findings are of interest to accounting firms, as well as clients and investors, to recognise the transformation of the status of the auditor in spite of regulations to protect the role.
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20.
  • Eklöv, Peter (författare)
  • Chemical cues from multiple predator-prey interactions induce changes in behavior and growth of anuran larvae
  • 2000
  • Ingår i: Oecologia. - : Springer Science and Business Media LLC. - 0029-8549 .- 1432-1939. ; 123:2, s. 192-199
  • Tidskriftsartikel (refereegranskat)abstract
    • Chemical signals are used as information by prey to assess predation risk in their environment. To evaluate the effects of multiple predators on prey growth, mediated by a change in prey activity, I exposed small and large bullfrog (Rana catesbeiana) larvae (tadpoles) to chemical cues from different combinations of bluegill sunfish (Lepomis macrochirus) and larval dragonfly (Anax junius) predators. Water was regularly transferred from predation trials (outdoor experiment) to aquaria (indoor experiment) in which activity and growth of tadpoles was measured. The highest predation mortality of small bullfrog larvae in the outdoor experiment was due to Anax, and it was slightly lower in the presence of both predators, probably resulting from interactions between predators. There was almost no mortality of prey with bluegill. The activity and growth of small bullfrog larvae was highest in the absence of predators and lowest in the presence of Anax. In the presence of bluegill only, or with both predators, the activity and growth of small bullfrog tadpoles was intermediate. Predators did not affect large tadpole activity and growth. Regressing mortality of small bullfrog tadpoles against activity and growth of bullfrog tadpoles revealed a significant effect for small bullfrog larvae but a non-significant effect for large bullfrog larvae. This shows that the response of bullfrog tadpoles to predators is related to their own body size. The experiment demonstrates that chemical cues are released both as predator odor and as alarm substances and both have the potential to strongly alter the activity and growth of prey. Different mechanisms by which chemical cues may be transmitted to species interactions in the food web are discussed.
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21.
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22.
  • Eklöv, Peter (författare)
  • Effects of habitat complexity and preyabundance on the spatial and temporaldistributions of perch (Perca fluviatilis)and pike (Esox lucius)
  • 1997
  • Ingår i: Canadian Journal of Fisheries and Aquatic Sciences. - : Canadian Science Publishing. - 0706-652X .- 1205-7533. ; 54:7, s. 1520-1531
  • Tidskriftsartikel (refereegranskat)abstract
    • Structurally complex environments strongly affect the behaviours and foraging efficiencies of predators and prey. I studied temporal variation in the habitat distribution of perch (Perca fluviatilis) and pike (Esox lucius) in relation to habitatcomplexity and prey abundance in a lake. The study involved quantitative estimates of different habitat types, estimates omacroinvertebrate prey availability, and distribution and movement patterns of the fish. The numbers of 80–110 mm perch in the littoral zone decreased rapidly in spring, which was a result of either perch moving to the pelagic zone or predation mortality. Predation mortality is the most plausible explanation because piscivorous perch and pike >160 mm aggregated close to these high abundances of 80–110 mm perch, and 80–110 mm perch used only vegetated habitats as a possible protection against predators. Both the biomass and diversity of macroinvertebrates increased with vegetation density, whereas perch abundance was highest in an intermediate vegetation density. Pike size was inversely related to vegetation density as a result of potential cannibalism from the largest pike individuals, which preferred the tree structure habitat. Perch group size decreased with increasing vegetation density, and perch <80 mm always occurred in group sizes larger than three individuals and never occurred in the same groups as perch >160 mm. In contrast, perch >160 mm occurred at decreasing numbers with increasing group size and mainly stayed solitary or in pairs. Perch >160 mm showed no tendencies for homing behaviour and moved actively around the whole lake, whereas pike showed a strong homing behaviour. My study suggests that the structural complexity in the littoral zone can both qualitatively and quantitatively change the interaction between piscivorous predators and their prey. La variation temporelle touchant la distribution de la perche commune (Perca fluviatilis) et du grand brochet (Esox lucius) dans l'habitat d'un lac a suggéré que la complexité structurale de la zone littorale puisse modifier, qualitativement et quantitativement, les interactions entre les prédateurs piscivores et leurs proies. Le nombre de perches de 80-110 mm dans la zone littorale a diminué rapidement au printemps. La mortalité par prédation est une explication plus plausible de ce phénomène que la migration des perches vers la zone pélagique parce que les percidés et les brochets piscivores de taille 160 mm se rassemblaient près de ces zones de forte abondance de petites perches (80-110 mm), qui n'utilisent que les habitats couverts de végétation comme protection possible contre les prédateurs. La biomasse et la diversité de macroinvertébrés ont augmenté avec la densité de la végétation, tandis que l'abondance des perches était la plus élevée lorsque la densité de la végétation était intermédiaire. La taille du grand brochet était inversement proportionnelle à la densité de la végétation en raison de la possibilité de cannibalisme par les brochets de plus grande taille qui préféraient un habitat comportant des arbres. La taille des perches, en groupe, diminuait avec l'augmentation de la densité de la végétation et les percidés de taille < 80 mm se présentaient toujours en groupe de plus de trois individus et jamais dans les mêmes groupes que les percidés > 160 mm. Ces derniers vivaient principalement en solitaires ou en paires, ne présentaient aucune tendance en ce qui a trait au comportement de retour, et se déplaçaient activement autour du lac entier; le grand brochet présentait un comportement de retour très prononcé. [Traduit par la Rédaction]
  •  
23.
  • Eklöv, Peter, et al. (författare)
  • Facilitation among piscivorous predators: effects of prey habitat use
  • 2001
  • Ingår i: Ecology. - 0012-9658. ; 82:9, s. 2486-2494
  • Tidskriftsartikel (refereegranskat)abstract
    • The combined effects of predators on prey may substantially differ from thatof each predator species alone because of alterations in prey behavior. Using enclosures within a pond, we examined experimentally the effects of two piscivorous predators on prey mortality and prey resource levels in two habitats. The two predators use two different foraging modes, which also allowed us to examine the behaviorally induced indirect effects of prey on predator growth and prey food resources. Both perch (Perca fluviatilis) and pike (Esox lucius) caused significant mortality of roach (Rutilus rutilus), and the combined predator mortality was higher than predicted from a multiplicative prey consumption model. Growth rates of perch were similar when enclosures contained only perch and when they contained perch combined with pike. The growth rate of pike was higher when they were together with perch compared to when alone. Growth of roach was similar among treatments. The invertebrate food resources of roach increased by a factor 10 in the open water but remained at similar levels throughout the experiment in the vegetation. Biomass of Daphnia longispina, the dominant zooplankton species in the open water, was strongly correlated with mortality of roach, indicating a density-mediated indirect effect of predators on prey resources. There was no indirect effect on D. longispina in the vegetation caused by habitat restriction of roach and only a weak relationship in the open water. There was a strong indirect effect of pike predation on macroinvertebrates induced by a habitat shift of roach. Our results suggest that there was facilitation between predators caused by conflicting antipredator behavior of roach, which resulted in density-mediated indirect effects on prey resources. The behavioral response of roach to the two predators also induced indirect effects on invertebrate prey.  
  •  
24.
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25.
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26.
  • Eklöv, Peter, et al. (författare)
  • Pike predators induce morphological changes in young perch and roach
  • 2007
  • Ingår i: Journal of Fish Biology. - : Wiley. - 0022-1112 .- 1095-8649. ; 70:1, s. 155-164
  • Tidskriftsartikel (refereegranskat)abstract
    • The morphological response of two 1 year-old prey species, perch Perca fluviatilis and roach Rutilus rutilus to the presence of predatory pike Esox lucius, was tested in a 6 week aquarium experiment. The growth of perch was higher than that of roach but there was no difference in growth of prey between predator and control treatments. The presence of pike caused morphological changes in both perch and roach. Perch showed an increase in body depth during the experiment whereas the morphological response of roach to pike was more related to a displacement of the dorsal and pelvic fins and width of the anal fin. Differences in morphological responses of perch and roach to pike can be interpreted by their overall differences in antipredator strategies.
  •  
27.
  • Eklöv, Peter, et al. (författare)
  • PISCIVORE EFFICIENCY AND REFUGING PREY - THE IMPORTANCE OF PREDATOR SEARCH MODE
  • 1994
  • Ingår i: Oecologia. - 0029-8549 .- 1432-1939. ; 98:3-4, s. 344-353
  • Tidskriftsartikel (refereegranskat)abstract
    • In predator-prey interactions, the efficiency of the predator is dependent on characteristics of both the predator and the prey, as well as the structure of the environment. In a field enclosure experiment, we tested the effects of a prey refuge on predator search mode, predator efficiency and prey behaviour. Replicated enclosures containing young of the year (0+) and 1-year-old (1+) perch were stocked with 3 differentially sized individuals of either of 2 piscivorous species, perch (Perca fluviatilis), pike (Esox lucius), or no piscivorous predators. Each enclosure contained an open predator area with three small vegetation patches, and a vegetated absolute refuge for the prey. We quantified the behaviour of the predators and the prey simultaneously, and at the end of the experiment the growth of the predators and the mortality and habitat use of the prey were estimated. The activity mode of both predator species was stationary. Perch stayed in pairs in the vegetation patches whereas pike remained solitary and occupied the corners of the enclosure. The largest pike individuals stayed closest to the prey refuge whereas the smallest individuals stayed farthest away from the prey refuge, indicating size-dependent interference among pike. Both size classes of prey showed stronger behavioural responses to pike than to perch with respect to refuge use, distance from refuge and distance to the nearest predator. Prey mortality was higher in the presence of pike than in the presence of perch. Predators decreased in body mass in all treatments, and perch showed a relatively stronger decrease in body mass than pike during the experiment. Growth differences of perch and pike, and mortality differences of prey caused by predation, can be explained by predator morphology, predator attack efficiency and social versus interference behaviour of the predators. These considerations suggest that pike are more efficient piscivores around prey refuges such as the littoral zones of lakes, whereas perch have previously been observed to be more efficient in open areas, such as in the pelagic zones of lakes.
  •  
28.
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29.
  • Eklöv, Peter, et al. (författare)
  • Predation risk influences adaptive morphological variation in fish populations
  • 2006
  • Ingår i: American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 167:3, s. 440-452
  • Tidskriftsartikel (refereegranskat)abstract
    • Predators can cause a shift in both density and frequency of a prey phenotype that may lead to phenotypic divergence through natural selection. What is less investigated is that predators have a variety of indirect effects on prey that could potentially have large evolutionary responses. We conducted a pond experiment to test whether differences in predation risk in different habitats caused shifts in behavior of prey that, in turn, would affect their morphology. We also tested whether the experimental data could explain the morphological variation of perch in the natural environment. In the experiment, predators caused the prey fish to shift to the habitat with the lower predation risk. The prey specialized on habitat-specific resources, and there was a strong correlation between diet of the prey fish and morphological variation, suggesting that resource specialization ultimately affected the morphology. The lack of differences in competition and mortality suggest that the morphological variation among prey was induced by differences in predation risk among habitats. The field study demonstrated that there are differences in growth related to morphology of perch in two different habitats. Thus, a trade-off between foraging and predator avoidance could be responsible for adaptive morphological variation of young perch.
  •  
30.
  •  
31.
  • Eklöv, Peter, et al. (författare)
  • SPECIES-SPECIFIC ANTIPREDATOR CAPACITIES AND PREY REFUGES - INTERACTIONS BETWEEN PISCIVOROUS PERCH (PERCA-FLUVIATILIS) AND JUVENILE PERCH AND ROACH (RUTILUS-RUTILUS)
  • 1995
  • Ingår i: Behavioral Ecology and Sociobiology. - 0340-5443 .- 1432-0762. ; 37:3, s. 169-178
  • Tidskriftsartikel (refereegranskat)abstract
    • The outcome of predator-prey interactions depends on the characteristics of predators and prey as well as the structure of the environment. In a replicated field enclosure experiment, we tested the effects of quantity and quality of different prey refuges (no structure, structure forming a partial refuge, and structure forming a complete refuge) on the interaction between piscivorous perch (Perca fluviatilis) and juvenile perch and roach (Rutilus rutilus). We quantified the behaviour of the predators and the prey and predator-induced prey mortality. The piscivores stayed in or close to the prey refuge and were more dispersed in the presence than in the absence of prey refuges. Survival of juvenile perch and roach decreased in the presence of predators and was higher for juvenile roach than for juvenile perch. In addition, juvenile perch survival increased with refuge efficiency. Roach formed schools which were denser in the presence of predators, had a higher swimming speed (both in the open water and in the refuge) and used a larger area than juvenile perch. Both prey species decreased their distance to the prey refuge and increased the proportion of their time spent in the refuge in the presence of predators. The number of switches between the open-water habitat and the prey refuge was higher for juvenile roach than for juvenile perch. Juvenile perch used different parts of the prey refuge in a flexible way depending both on presence of predators and refuge type whereas juvenile roach used the different parts of the prey refuge in fixed proportions over all refuge treatments. Our results suggest that juvenile roach had a overall higher capacity to avoid predation than juvenile perch. However, in the presence of qualitatively different prey refuges juvenile perch responded to predators with more flexible refuge use than juvenile roach. The differences in antipredator capacities of juvenile perch and roach when subjected to piscivorous perch predation may depend on differences in life history patterns of the two species.
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32.
  • Eklöv, Peter, et al. (författare)
  • The response of prey to the risk of predation : Proximate cues for refuging juvenile fish
  • 1996
  • Ingår i: Animal Behaviour. - UMEA UNIV,DEPT ANIM ECOL,S-90187 UMEA,SWEDEN. : Elsevier BV. - 0003-3472 .- 1095-8282. ; 51, s. 105-115
  • Tidskriftsartikel (refereegranskat)abstract
    • When prey encounter predators, they use different cues to indicate how to respond to minimize the predation risk. How such proximate cues in the environment correspond to the ultimate behaviour of the prey are important for understanding the outcome of predator-prey interactions. The precision of the anti-predator response of juvenile perch, Perca fluviatilis, and roach, Rutilus rutilus, when subjected to predation by piscivorous perch and pike, Esox lucius, and to different types of structure was tested in a wading pool experiment. The predation risk was varied between two habitats (one open water and one structured) by confining the predators to one of the two habitats. The prey were free to choose between habitats. Both perch and pike attacked both prey species but they were only successful in capturing roach. Roach swam faster than juvenile perch in the presence of perch, whereas juvenile perch swam faster than roach in the presence of pike. Juvenile perch inspected the predators more and showed a more flexible inspection behaviour than did roach. Juvenile perch decreased the number of switches between habitats and stayed in the predator-free part of the pool in the presence of perch. In contrast, roach increased their habitat switch frequency in the presence of perch and stayed in the vegetation structure even when there were perch there. Both prey species preferred to stay in the vegetation structure when pike were there. Juvenile perch used both the vegetation and pipe structure as refuges whereas roach used only the vegetation structure as a refuge. The results suggest that juvenile perch use a different cue when assessing predation risk and display a more flexible behaviour compared with roach which simply move into vegetation under the threat of predation irrespective of predator location. (C) 1996 The Association for the Study of Animal Behaviour
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33.
  • Eklöv, Peter, et al. (författare)
  • The trade-off between foraging activity and predation risk for Rana temporaria in different food environments
  • 2000
  • Ingår i: Canadian Journal of Zoology. - : Canadian Science Publishing. - 0008-4301 .- 1480-3283. ; 78:5, s. 734-739
  • Tidskriftsartikel (refereegranskat)abstract
    •  We evaluated the trade-off between foraging activity and predation risk for larvae of an anuran species presented with different types of food resources. In the laboratory we examined the effects of benthic and phytoplankton resources and the two types combined on the activity and mortality of larvae of the common frog, Rana temporaria, exposed to predatory larva, Dytiscus marginalis.Predation mortality of tadpoles increased with the duration of the experiment and was highest in the presence of the phytoplankton resource alone. This was explained by a decrease in prey activity in the benthic- and combined-resource treatments when the predator was present, whereas in the phytoplankton treatment, the activity of the tadpoles were similar in the presence or absence of the predator.In the presence of the predator, prey mainly used the bottom of the aquarium in the benthic- and combined-resource treatments. In contrast, in the phytoplankton treatment they used the water column more than in the other treatments. In the presence of the predator, the prey had a lower consumption rate in the phytoplankton treatment than in the other treatments.Predator activity did not change among treatments. The results suggest that the trade-off between foraging activity and predation mortality for anuran larvae is strongly affected by the types of food resources present in the environment.  
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34.
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35.
  • Faulks, Leanne, et al. (författare)
  • Genetic and morphological divergence along the littoral–pelagic axis in two common and sympatric fishes : perch, Perca fluviatilis (Percidae) and roach, Rutilus rutilus (Cyprinidae)
  • 2015
  • Ingår i: Biological Journal of the Linnean Society. - : Oxford University Press (OUP). - 0024-4066 .- 1095-8312. ; 114:4, s. 929-940
  • Tidskriftsartikel (refereegranskat)abstract
    • Individuals are constantly in competition with one another and, on both ecological and evolutionary timescales, processes act to reduce this competition and promote the gain of fitness advantages via diversification. Here we have investigated the genetic (AFLP) and morphological (geometric morphometrics) aspects of the littoral–pelagic axis, a commonly observed resource polymorphism in freshwater fishes of postglacial lakes. We found a large degree of variation in the genetic and morphological divergence between littoral and pelagic perch and roach across Swedish lakes. Although there was evidence of assortative mating (elevated kinship values) in both species, we could not find any significant coupling of morphology and genetic divergence. Instead, there was evidence that the extent of resource polymorphism may be largely caused by phenotypic plasticity. These results suggest that assortative mating, which can lead to genetically determined adaptive divergence, does occur in these species, particularly perch, but not according to genetically fixed morphological traits. The behavioural mechanisms facilitating associative mating need to be investigated to explore the interaction between phenotypic plasticity and adaptive genetic divergence and their roles in diversification.
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36.
  • Faulks, Leanne, et al. (författare)
  • Intraspecific Niche Variation Drives Abundance-Occupancy Relationships in Freshwater Fish Communities
  • 2015
  • Ingår i: American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 186:2, s. 272-283
  • Tidskriftsartikel (refereegranskat)abstract
    • A positive relationship between occupancy and average local abundance of species is found in a variety of taxa, yet the mechanisms driving this association between abundance and occupancy are still enigmatic. Here we show that freshwater fishes exhibit a positive abundance-occupancy relationship across 125 Swedish lakes. For a subset of 9 species from 11 lakes, we estimated species-specific diet breadth from stable isotopes, within-lake habitat breadth from catch data for littoral and pelagic nets, adaptive potential from genetic diversity, abiotic niche position, and dispersal capacity. Average local abundance was mainly positively associated with both within-lake habitat and diet breadth, that is, species with larger intraspecific variation in niche space had higher abundances. No measure was a good predictor of occupancy, indicating that occupancy may be more directly related to abundance or abiotic conditions than to niche breadth per se. This study suggests a link between intraspecific niche variation and a positive abundance-occupancy relationship and implies that management of freshwater fish communities, whether to conserve threatened or control invasive species, should initially be aimed at niche processes.
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37.
  • Hedström, Per, 1974- (författare)
  • Climate change impacts on production and dynamics of fish populations
  • 2016
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Ongoing climate change is predicted to increase water temperatures and export of terrestrial dissolved matter (TDOM) to aquatic ecosystems influencing ecosystem productivity, food web dynamics and production of top consumers. Ecosystem productivity is mainly determined by the rates of primary production (GPP) in turn controlled by nutrients, light availability and temperature, while temperature alone affect vital rates like consumption and metabolic rates and maintenance requirements of consumers. Increased level of TDOM causes brownification of water which may cause light limitation in algae and decrease GPP and especially so in the benthic habitat. Temperature increase has a been suggested to increase metabolic rates of consumers to larger extent than the corresponding effect on GPP, which suggest reduced top consumer biomass and production with warming.The aim of this thesis was to experimentally study the effects of increased temperature and TDOM on habitat specific and whole ecosystem GPP and fish densities and production. In a replicated large-scale pond experiment encompassing natural food webs of lotic ecosystems I studied population level responses to warming and brownification in the three- spined stickleback (Gasterosteus aculeatus).Results showed overall that warming had no effect on whole ecosystem GPP, likely due to nutrient limitation, while TDOM input decreased benthic GPP but stimulated pelagic GPP. In fish, results first of all suggested that recruitment in sticklebacks over summer was negatively affected by warming as maintenance requirements in relation to GPP increased and thereby increased starvation mortality of young-of-the-year (YOY) sticklebacks. Secondly, brownification increased mortality over winter in YOY as the negative effect on light conditions likely decreased search efficiency and caused lower consumption rates and starvation over winter in sticklebacks. Third, seasonal production of YOY, older, and total stickleback production was negatively affected by warming, while increased TDOM caused decreased YOY and total fish production. The combined effect of the two was intermediate but still negative. Temperature effects on fish production were likely a result of increased energy requirements of fish in relation to resource production and intake rates whereas the negative effect of TDOM likely was a result of decreased benthic resource production. Finally, effects of warming over a three-year period caused total fish density and biomass and abundance of both mature and old fish to decrease, while proportion of young fish increased. The main cause behind the strong negative effects of warming on fish population biomass and changes in population demographic parameters were likely the temperature driven increased energy requirements relative to resource production and cohort competition.The results from this thesis suggest that predicted climate change impacts on lentic aquatic ecosystems will decrease future densities and biomass of fish and negatively affect fish production and especially so in systems dominated by benthic resource production.
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38.
  • Hirsch, Philipp E, et al. (författare)
  • Indirect trophic interactions with an invasive species affect phenotypic divergence in a top consumer
  • 2013
  • Ingår i: Oecologia. - : Springer Science and Business Media LLC. - 0029-8549 .- 1432-1939. ; 172:1, s. 245-256
  • Tidskriftsartikel (refereegranskat)abstract
    • While phenotypic responses to direct species interactions are well studied, we know little about the consequences of indirect interactions for phenotypic divergence.In this study we used lakes with and without the zebra mussel to investigate effects ofindirect trophic interactions on phenotypic divergence between littoral and pelagic perch. We found a greater phenotypic divergence between littoral and pelagic individuals inlakes with zebra mussels and propose a mussel-mediated increase in pelagic and benthic resource availability as a major factor underlying this divergence. Lakes withzebra mussels contained higher densities of large plankton taxa and large invertebrates. We suggest that this augmented resource availability improved perch foraging opportunities in both the littoral and pelagic zones. Perch in both habitats could hence express a more specialized foraging morphology, leading to an increased divergence of perch forms in lakes with zebra mussels. As perch do not prey on mussels directly, we conclude that the increased divergence results from indirect interactions with the mussels. Our results hence suggest that species at lower food web levels can indirectlyaffect phenotypic divergence in species at the top of the food chain.
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39.
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40.
  • Höök, Tomas O., et al. (författare)
  • Sex-specific plasticity in a trophic polymorphic aquatic predator : a modeling approach
  • 2021
  • Ingår i: Oecologia. - : Springer. - 0029-8549 .- 1432-1939. ; 195:2, s. 341-354
  • Tidskriftsartikel (refereegranskat)abstract
    • Phenotypic plasticity is common among animal taxa. While there are clearly limits and likely costs to plasticity, these costs are unknown for most organisms. Further, as plasticity is partially genetically determined, the potential magnitude of exhibited plasticity may vary among individuals. In addition to phenotypic plasticity, various animal taxa also display sexual size dimorphism, a feature ultimately thought to arise due to differential size-dependent fitness costs and benefits between sexes. We hypothesized that differential selection acting on males and females can indirectly select for unequal genetically defined plasticity potential between the sexes. We evaluate this possibility for Eurasian perch (Perca fluviatilis), a species that displays modest sexual size dimorphism and habitat-related morphological plasticity. Using 500-year simulations of an ecogenetic agent-based model, we demonstrate that genetically determined morphological plasticity potential may evolve differently for males and females, leading to greater realized morphological variation between habitats for one sex over the other. Genetically determined potential for plasticity evolved differently between sexes across (a) various sex-specific life-history differences and (b) a variety of assumed costs of plasticity acting on both growth and survival. Morphological analyses of Eurasian perch collected in situ were consistent with model predictions: realized morphological variation between habitats was greater for females than males. We suggest that due to sex-specific selective pressures, differences in male and female genetically defined potential for plasticity may be a common feature across organisms.
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41.
  • Jane, Stephen F., et al. (författare)
  • Responses by benthic invertebrate community composition to dissolved organic matter in lakes decline substantially above a threshold concentration
  • 2024
  • Ingår i: Freshwater Biology. - : John Wiley & Sons. - 0046-5070 .- 1365-2427. ; 69:2, s. 288-299
  • Tidskriftsartikel (refereegranskat)abstract
    • Dissolved organic matter (DOM), often measured as dissolved organic carbon (DOC), plays a fundamental role in influencing the structure and function of lake ecosystems. Due to the myriad ecosystem effects of DOM, widespread observations of long-term increasing DOM concentrations have received much attention from ecologists. DOM positively influences primary production and consumer production at low concentrations due to the fertilising influence of bound nutrients. However, beyond a unimodal peak in production, a reduced light environment may result in a negative effect on production. This unimodal model has been largely developed and tested in lakes with low to moderate DOM concentrations (i.e., typically ≤ 10 mg/L DOC).To understand ecological responses in lakes across a larger range in DOM concentrations, we examined the response of benthic invertebrate communities in 148 Swedish lakes with DOM concentrations ranging between 0.67 and 32.77 mg/L DOC.We found that increasing DOM concentrations had a strong effect on invertebrate community composition below c. 10 mg/L. Across this range, abundances of individual taxa both increased and decreased, probably in response to environmental change induced by DOM. However, in lakes above this concentration, increasing DOM had minimal influence on community composition.As DOM concentrations continue to increase, faunal communities in lakes below this 10 mg/L DOC threshold are likely to undergo substantial change whereas those above this threshold are likely to be minimally impacted.
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42.
  • Liess, Antonia, et al. (författare)
  • Food web complexity affects stoichiometric and trophic interactions
  • 2006
  • Ingår i: Oikos. - : Wiley. - 0030-1299 .- 1600-0706. ; 114:1, s. 117-125
  • Tidskriftsartikel (refereegranskat)abstract
    • The stoichiometry of trophic interactions has mainly been studied in simple consumer–prey systems, whereas natural systems often harbour complex food webs with abundant indirect effects. We manipulated the complexity of trophic interactions by using simple laboratory food webs and complex field food webs in enclosures in Lake Erken. In the simple food web, one producer assemblage (periphyton) and its consumers (benthic snails) were amended by perch, which was externally fed by fish food. In the complex food web, two producer assemblages (periphyton and phytoplankton), their consumers (benthic invertebrates and zooplankton) and perch feeding on zooplankton were included. In the simple food web perch affected the stoichiometry of periphyton and increased periphyton biomass and the concentration of dissolved inorganic nitrogen. Grazers reduced periphyton biomass but increased its nutrient content. In the complex food web, in contrast to the simple food web, perch affected periphyton biomass negatively but increased phytoplankton abundance. Perch had no influence on benthic invertebrate density, zooplankton biomass or periphyton stoichiometry. Benthic grazers reduced periphyton biomass and nutrient content. The difference between the simple and the complex food web was presumably due to the increase of pelagic cyanobacteria (Gloeotrichia sp.) with fish presence in the complex food web, thus fish had indirect negative effects on periphyton biomass through nutrient competition and shading by cyanobacteria. We conclude that the higher food web complexity through the presence of pelagic primary producers (in this case Gloeotrichia sp.) influences the direction and strength of trophic and stoichiometric interactions.
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43.
  • Liess, Antonia, 1975- (författare)
  • Nutrient Stoichiometry in Benthic Food Webs – Interactions Between Algae, Herbivores and Fish
  • 2006
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • The aim of this thesis was to identify general structuring mechanisms in benthic food webs within the framework of ecological stoichiometry theory. Ecological stoichiometry is defined as the balance of multiple chemical substances in ecological interactions and explicitly considers the combined dynamics of key elements such as carbon (C), nitrogen (N) and phosphorus (P). Ecological stoichiometry theory was developed for pelagic environments, thus it must be tested whether the same mechanisms are applicable to benthic environments. In this thesis, ecological stoichiometry theory was used as a framework to investigate nutrient pathways in benthic littoral ecosystems. I conducted one invertebrate field sampling and six experiments. In the experiments, factors such as grazing, light, nutrients and fish presence were manipulated. The results showed that stoichiometric variability in consumers could mostly be explained by taxa. However, there was some stoichiometric variability due to sampling season, site, and nutrient enrichment. Grazing mostly increased periphyton N and P content, although nutrient recycling effects were dependent on grazer stoichiometry. Grazing changed benthic algal community composition by increasing the proportion of grazing resistant algae species. Additionally, grazing decreased algal diversity, especially under nutrient poor conditions. The manipulation of fish presence revealed that fish affected primary producer biomass and stoichiometry through nutrient recycling. The manipulation of abiotic factors, such as light and nutrient addition could affect periphyton nutrient content, biomass and benthic algal chlorophyll a content. The separate addition of N or P led to an increase of the added nutrient in the periphyton. Increased light intensities led to a decreased cellular chlorophyll a content and increased C:nutrient ratios. This thesis arrives at the conclusion that periphyton-grazer-predator interactions in the benthic are bound by stoichiometric constraints. Nutrient recycling by benthic invertebrates and fish are important mechanism in benthic littoral ecosystems.
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44.
  • Lönnstedt, Oona, et al. (författare)
  • Environmentally relevant concentrations of microplastic particles influence larval fish ecology
  • 2016
  • Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 352:6290, s. 1213-1216
  • Tidskriftsartikel (refereegranskat)abstract
    • The widespread occurrence and accumulation of plastic waste in the environment have become a growing global concern over the past decade. Although some marine organisms have been shown to ingest plastic, few studies have investigated the ecological effects of plastic waste on animals. Here we show that exposure to environmentally relevant concentrations of microplastic polystyrene particles (90 micrometers) inhibits hatching, decreases growth rates, and alters feeding preferences and innate behaviors of European perch (Perca fluviatilis) larvae. Furthermore, individuals exposed to microplastics do not respond to olfactory threat cues, which greatly increases predator-induced mortality rates. Our results demonstrate that microplastic particles operate both chemically and physically on larval fish performance and development.
  •  
45.
  • Marklund, Maria H. K., et al. (författare)
  • Asymmetrical habitat coupling of an aquatic predator : The importance of individual specialization
  • 2019
  • Ingår i: Ecology and Evolution. - : Wiley. - 2045-7758. ; 9:6, s. 3405-3415
  • Tidskriftsartikel (refereegranskat)abstract
    • Predators should stabilize food webs because they can move between spatially separate habitats. However, predators adapted to forage on local resources may have a reduced ability to couple habitats. Here, we show clear asymmetry in the ability to couple habitats by Eurasian perch—a common polymorphic predator in European lakes. We sampled perch from two spatially separate habitats—pelagic and littoral zones—in Lake Erken, Sweden. Littoral perch showed stronger individual specialization, but they also used resources from the pelagic zone, indicating their ability to couple habitats. In contrast, pelagic perch showed weaker individual specialization but near complete reliance on pelagic resources, indicating their preference to one habitat. This asymmetry in the habitat coupling ability of perch challenges the expectation that, in general, predators should stabilize spatially separated food webs. Our results suggest that habitat coupling might be constrained by morphological adaptations, which in this case were not related to genetic differentiation but were more likely related to differences in individual specialization.
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46.
  • Marklund, Maria H. K., et al. (författare)
  • Habitat coupling mediates trophic cascades in an aquatic community
  • 2019
  • Ingår i: Ecosphere. - : Wiley. - 2150-8925 .- 2150-8925. ; 10:9
  • Tidskriftsartikel (refereegranskat)abstract
    • Trophic cascades and other indirect effects can significantly mediate community interactions. Movement of energy between systems has been shown to be important for trophic cascades in food webs, where coupling between habitats can be important for food web stability and species evenness. To investigate the effects of habitat coupling on the stability and dynamics of chlorophyll a (used as a proxy for phytoplankton biomass), mediated by the abundance and composition of zooplankton and macroinvertebrates, we manipulated habitat use by the predator perch. We show a greater indirect effect of predation on phytoplankton abundance when no habitat coupling occurs, indicating a stronger predation effect and a decrease in zooplankton grazing pressure leading to an increase in phytoplankton biomass. Although we found a significant effect on chlorophyll a between the treatments, this effect was not evident in the abundance of prey resources of perch (zooplankton and macroinvertebrates). Other indirect effects, not measured in this study, such as compositional changes in prey groups, could potentially explain the lack of effect in prey resources. While there is a strong theoretical argument for the stabilizing effects of habitat coupling, empirical evidence is scarce. Our study offers tentative support for these theoretical predictions in a natural system.
  •  
47.
  • Marklund, Maria H. K., et al. (författare)
  • The influence of habitat accessibility on the dietary and morphological specialisation of an aquatic predator
  • 2018
  • Ingår i: Oikos. - : John Wiley & Sons. - 0030-1299 .- 1600-0706. ; 127:1, s. 160-169
  • Tidskriftsartikel (refereegranskat)abstract
    • Individual diet and habitat specialisation are widespread in animal taxa and often related to levels of predation and competition. Mobile consumers such as predatory fish can stabilise lake food webs by ranging over a larger area than their prey, thereby switching between habitats. Although, this switching assumes that the predator has equal preference for the available prey, individual diet specialisation and morphological adaptations to different habitats could potentially prevent individuals from switching between habitats. In this study, we assessed the niche width and individual specialisation in Eurasian perch Perca fluviatilis in response to a shift in habitat use by manipulating the ability for this top predator to couple habitats. We ran an eight weeks pond experiment, to test the effect of habitat switching on diet and morphological specialisations. We show that habitat coupling influenced individual diet specialisation and niche use in expected directions where specialisation increased with decreasing habitat switching. In contrast to expectations, the morphological variation decreased with increasing diet specialisation. Our results expand on previous work and suggest that individual specialisation and niche width can impact the ability of mobile predators to couple habitats. Furthermore, it shows the importance of individual specialisations in relation to habitat coupling.
  •  
48.
  • Marklund, Maria H. K. (författare)
  • The influence of trophic polymorphisms on habitat coupling in aquatic food webs
  • 2017
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Trophic cascades, together with other indirect interactions are important aspects in shaping the composition and abundance of species in the food web. Theoretically, movement of energy between systems, and coupling between habitats by mobile predators have been suggested as being important for food web stability and evenness. Individual diet specialisations have been shown to be widespread in many animal taxa. Although not widely studied, some studies have indicated that mobile predators that display individual specialisations, may have a reduced ability to couple habitats.In this thesis, by using field studies and an experimental study, my aim was to assess the individual specialisation displayed by Eurasian perch (Perca fluviatilis) and its influence on the ability of the perch to couple habitats. In the experiment, we also investigated the effect of habitat coupling, or the lack of habitat coupling, on the dynamics and stability of the resources in the ecosystem.We show that habitat diversity and resource availability influenced perch individual specialisation and morphological variation. We found that the perch total niche width decreased with decreasing habitat switching ability. We demonstrate asymmetrical habitat coupling ability in perch across pelagic and littoral habitats, providing evidence that not all individuals within a species respond in the same way when it comes to spatial coupling and thereby providing stability within a food web.Our results expand on previous work and suggest that habitat coupling ability can influence individual specialisations and niche width. Furthermore, we show the importance of individual specialisations in relation to habitat coupling. Finally, we provide evidence for the theory that a food web dominated by a food specialist should exhibit more variable resource dynamics than a food web dominated by a generalist predator by showing a greater indirect effect of predation on the phytoplankton levels when no habitat coupling occurs. While many models and theoretical concepts have proposed a stabilising effect of cross movement of energy and mobile predators, little empirical evidence exists that confirms this mechanism.In conclusion, my thesis gives some support for the theoretical predictions that habitats coupled by a generalist predator should be more stable.
  •  
49.
  • Naddafi, Rahmat, et al. (författare)
  • Effects of the zebra mussel, an exotic freshwater species, on seston stoichiometry
  • 2008
  • Ingår i: Limnology and Oceanography. - : American Society of Limnology and Oceanography. - 0024-3590 .- 1939-5590. ; 53:5, s. 1973-1987
  • Tidskriftsartikel (refereegranskat)abstract
    • We examined the effect of the zebra mussel, Dreissena polymorpha, an exotic species, on seston stoichiometry by conducting laboratory experiments in which we varied nutrient composition of seston and mussels over time. Zebra mussels altered the stoichiometry of seston through removal of particulate organic nutrients and changed the stoichiometry of the dissolved nutrient pool through nutrient excretion. Grazers had stronger effects on carbon : phosphorus (C : P) and nitrogen (N) : P ratios than on the C:N ratio of seston. Elemental residence time in tissue and high mass-specific nutrient excretion by small mussels caused small mussels to be more efficient nutrient recyclers than larger mussels. Zebra mussels reduced P availability through enhancing C: P and N: P molar ratios of seston during the period extending from June to August, when P was limited in the lake, and increased the C:N molar ratio of seston in June, when N was at the minimum level in the lake. C: P and N: P molar ratios for zebra mussel tissue were higher in August and somewhat in September than in all other months. N was retained more efficiently than P in Dreissena tissue. Nutrient mass-specific uptake rate was higher than excretion rate by zebra mussels.
  •  
50.
  • Naddafi, Rahmat, et al. (författare)
  • Non-lethal predator effects on the feeding rate and prey selection of the exotic zebra mussel (Dreissena polymorpha)
  • 2007
  • Ingår i: Oikos. - 0030-1299 .- 1600-0706. ; 116:8, s. 1289-1298
  • Tidskriftsartikel (refereegranskat)abstract
    • Predators may induce changes in prey feeding that indirectly influence both the impact of prey on resource abundances and their interactions with other species in their community. We evaluated whether clearance and excretion (faeces plus pseudofaeces) of phytoplankton by zebra mussels were affected by the presence of predatory cues from roach (Rutilus rutilus) and signal crayfish (Pasifastacus leniusculus). We found that non-lethal effects of predators can alter zebra mussel clearance rate and thus the impact of zebra mussels on phytoplankton. Risk cues released by both predators had similar negative effects on clearance rate of zebra mussels and cascading positive indirect effects on phytoplankton resources. Predation risk had a stronger effect on zebra mussels' clearance rate of cyanobacteria and diatoms than cryptophytes and chrysophytes. The presence of predators did not significantly affect the rate at which zebra mussels expelled and excreted phytoplankton, although there was a tendency for more chlorophyll to be expelled and excreted in the presence of predators. Our results contribute to the growing evidence that predators indirectly affect resource dynamics and food web structure through their non-lethal effects on consumers. Our results suggest that exotic species such as zebra mussels can show behavioural responses to both native (e.g., roach) and exotic (e.g., crayfish) predators.
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