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Aerobic anoxygenic phototrophs (AAP) are a group of photoheterotrophic bacteria that use sunlight as a supplemental energy source, allowing them to be found in many illuminated environments. Here, we investigated their presence in Lake Winnipeg, Manitoba, Canada with spatial and temporal considerations to define the niche that they fill, and understand the biogeochemical pathways influenced or controlled by AAP. In addition, we explored their diversity and expanded upon the range of photosynthetic arrangements known, by looking into a variety of newly purified pigmented isolates to assess unique characteristics, all of which allowed us to better understand the AAP group as a whole. We described seasonal trends of microbial communities in Lake Winnipeg, where up to 1.49% of the sequenced community and 19.1% of the total culturable copiotrophic heterotrophs were AAP at littoral zones during their peak spring season, and they directly followed sunlight availability. Isolated and purified strains were capable of several metal transformations, including metal(loid) oxide reduction and production of siderophores or metallophores. This widespread physiology, particularly among lake isolates, suggested a potential ecological importance for AAP involving a metal(loid) collecting niche. AAP with elongated cells were established as both associated to, and possibly preyed upon by filter feeding mollusks Dreissena polymorpha, which provided insights into how these bacteria interact with the foodweb. Many pigmented and phylogenetically diverse strains were discovered from across the lakes euphotic zones. Representatives of each different species were physiologically, morphologically and phylogenetically compared and described, showing members of specific taxonomic families all shared heritable traits including pigments. This confirmed evolutionary age of photosynthesis in AAP, and suggested recent horizontal gene transfer events did not occur. Furthermore, unusual aerobic violet

Nitrogen and carbon stable isotope data sets are commonly used to assess complex population to ecosystem responses to natural or anthropogenic changes at regional to global spatial scales, and monthly to decadal timescales. Measured in the tissues of consumers, nitrogen isotopes (δ15N) are primarily used to estimate trophic position while carbon isotopes (δ13C) describe habitat associations and feeding pathways. Models of both δ15N and δ13C values and their associated variance can be used to estimate likely dietary contributions and niche width and provide inferences about consumer movement and migration. Stable isotope data have added utility when used in combination with other empirical data sets (e.g., stomach content, movement tracking, bioregionalization, contaminant, or fisheries data) and are increasingly relied upon in food web and ecosystem models. While numerous regional studies publish tables of mean δ15N and δ13C values, limited individual records have been made available for wider use. Such a deficiency has impeded full utility of the data which otherwise would facilitate identification of macroscale patterns. The data provided here consist of 4,498 records of individuals of three tuna species, Thunnus alalunga, T. obesus, and T. albacares sampled from all major ocean basins from 2000 to 2015. For each individual tuna we provide a record of the following: species name, sampling date, sampling location, tuna length, muscle bulk and baseline corrected δ15N values, and muscle bulk and, where available, lipid corrected δ13C values. We provide these individual records to support comparative studies and more robust modelling projects seeking to improve understanding of complex marine ecosystem dynamics and their responses to a changing environment. There are no copyright restrictions for research and/or teaching purposes. Users are requested to acknowledge their use of the data in publications, research proposals, websites and other outlets following the cita

Thiamin (vitamin B1) is required for several life-sustaining processes in most organisms and cells, e.g. in the conversion of food to energy. It also serves as an antioxidant and is important for proper nerve signaling. Thiamin is produced predominantly by bacteria and phytoplankton in the aquatic food web. Not all bacteria and phytoplankton, nor any organisms in higher trophic levels can produce thiamin; instead, they rely on a continuous external supply and uptake of this essential compound. Thiamin deficiencies occur episodically in a wide range of taxa, especially in higher trophic levels. In the Baltic Sea, thiamin deficiencies has been most pronounced in salmon (Salmo salar) and recently deficiencies are also reported for other fish species and birds. This thesis focuses on thiamin dynamics in lower trophic levels, covering primary producers as well as primary consumers, as this topic has not received much attention previously. Thiamin content of common phytoplankton and zooplankton species and the transfer between them was investigated in experiments and field studies. The relationship between thiamin deficiency and underlying environmental factors was also investigated using monitoring data. Thiamin content differed among phytoplankton classes, species and even strains. Filamentous Cyanophyceae had considerably higher thiamin content than other classes. However, thiamin transfer to copepods was lower, probably associated with difficulties ingesting the filaments. Moreover, thiamin content in seston varied seasonally, being highest during summer when both Prymnesiophyceae and filamentous Cyanophyceae were more abundant. Thiamin content in the two size fractions correlated strongly and was always higher in the smaller size fraction, illustrating the importance of picoplankton and bacteria in the food web. Also, seston thiamin content was higher in the Baltic Proper than in the Skagerrak. Copepods differed in thiamin content among genera, as well as between loc, Tiamin (vitamin B1) är nödvändigt för flera livsuppehållande processer i cellerna hos det stora flertalet organismer, t.ex. vid omvandling av näring till energi. Vitaminet fungerar också som en antioxidant och är viktigt för korrekt nervfunktion. I den akvatiska födoväven produceras tiamin i första hand av bakterier och växtplankton. Dock inte av alla bakterier och växtplankton, utan dem, liksom organismer från högre trofiska nivåer, måste förlita sig på kontinuerlig tillgång samt upptag av detta livsviktiga ämne. Perioder av tiaminbrist har observerats i flera olika djurgrupper, speciellt i högre trofiska nivåer. I Östersjön har tiaminbrist varit mest utbrett i lax (Salmo salar) och har på senare tid även rapporterats för andra fiskarter och fåglar. Denna avhandling fokuserar på dynamiken av tiamin i lägre trofiska nivåer, såsom primärproducenter men även primärkonsumenter eftersom den största delen av tidigare forskning fokuserat på de högre trofiska nivåerna. Tiamininnehållet i vanligt förekommande växt- och djurplankton samt överföringen av tiamin mellan de trofiska nivåerna har undersökts i både experiment och fältstudier. Sambandet mellan tiaminbrist och underliggande miljöfaktorer har även undersökts genom att flerårig övervakningsdata analyserats. Tiaminnivåerna skiljde sig åt mellan olika växtplanktonklasser, mellan arter och även mellan olika isolat av samma art. Filamentösa (trådformiga) cyanobakterier hade betydligt högre tiamininnehåll än övriga växtplankton. Dock var överföringen av tiamin lägre från cyanobakterier till djurplankton jämfört med andra arter, förmodligen på grund av svårigheter att konsumera filamenten. I övrigt så varierade partikulärt bundet tiamin (s.k. seston) säsongsmässigt och var högst under sommaren när både Prymnesiophyceae och filamentösa cyanobakterier utgjorde en stor del av växtplanktonsamhället. Det var en stark korrelation mellan tiaminnivåerna i de två olika storleksfraktionerna av seston och det var alltid högre koncentr

Northern Pike (Esox lucius (Linnaeus, 1758)) and Lake Trout (Salvelinus namaycush (Walbaum, 1792)) are important apex predatory fish species that have ubiquitous distributions across Canada. While these species have been well studied due to their economic value, there remains considerable uncertainty around the influence of prey community dynamics on their growth and life history variation across the Canadian Boreal Shield. I investigated how changes and differences in prey community dynamics of Boreal Shield lakes influence the growth and life history traits expressed by these apex predators to further understand how their life history strategies have evolved, as well as how their life history strategies might shift in the face of environmental change. Broad geographic comparisons among Northern Pike populations revealed evidence for a widespread generalist foraging strategy, one that takes advantage of the availability of offshore Cisco (Coregonus artedi (Lesueur, 1818)). Similar to the offshore predator Lake Trout, Northern Pike reached larger asymptotic lengths in lakes with greater abundances of Cisco. Northern Pike additionally exhibited slower early growth rates and lower mortality rates in lakes with greater abundances of Cisco. In the absence of larger offshore prey fish, Lake Trout growth appears to be strongly influenced by the availability of nearshore prey fish in Boreal Shield lakes. Following an increase in the productivity of cyprinids in an experimental lake, the early growth rates of Lake Trout increased significantly, with the greatest amount of growth occurring after a switch to piscivory at age 2. With a variety of stressors threatening the health and stability of aquatic ecosystems, this research provides vital information pertaining to the influence of prey community dynamics on the growth potential and life history variation of aquatic apex predators in the Canadian Boreal Shield.

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.

Marine protected areas (MPAs) can potentially impact food web dynamics by increasing the density of predatory fishes within their borders. Such increases in density can cause shifts in the prey use of generalist predators. This study investigated the effects of increased conspecific density on the diet of Gopher Rockfish (Sebastes carnatus) at a 35-year-old MPA at Point Lobos and four newly established central California MPAs at Año Nuevo, Point Lobos, Piedras Blancas, and Point Buchon. Analysis of 710 stomachs collected in 2007-2009 indicated the most important overall prey were crabs, especially the family Pisidae and genus Cancer, as well as brittle stars and mysids. Diets did not differ inside versus outside the old Point Lobos MPA in terms of prey richness, evenness, composition, or Gopher Rockfish trophic level. Individual specialization, however, was greater outside the MPA. No consistent differences in these metrics were observed inside versus outside the four new MPAs, although prey evenness and composition did differ significantly among geographic locations. Diets at Año Nuevo, the most northern and shallow collection location, were dominated by Cancer crabs and porcelain crabs, while diets from southern, deeper locations were dominated by brittle stars. The case study of the old Point Lobos MPA indicates that changes in fish feeding ecology in MPAs may take decades to occur, if at all. Differences in prey observed among geographic locations suggest variation in the community composition among central California’s new MPAs, which may influence the effect of each MPA on food web dynamics over time.

A large number and wide variety of lake ecosystem models have been developed and published during the past four decades. We identify two challenges for making further progress in this field. One such challenge is to avoid developing more models largely following the concept of others ('reinventing the wheel'). The other challenge is to avoid focusing on only one type of model, while ignoring new and diverse approaches that have become available ('having tunnel vision'). In this paper, we aim at improving the awareness of existing models and knowledge of concurrent approaches in lake ecosystem modelling, without covering all possible model tools and avenues. First, we present a broad variety of modelling approaches. To illustrate these approaches, we give brief descriptions of rather arbitrarily selected sets of specific models. We deal with static models (steady state and regression models), complex dynamic models (CAEDYM, CE-QUAL-W2, Delft 3D-ECO, LakeMab, LakeWeb, MyLake, PCLake, PROTECH, SALMO), structurally dynamic models and minimal dynamic models. We also discuss a group of approaches that could all be classified as individual based: super-individual models (Piscator, Charisma), physiologically structured models, stage-structured models and trait-based models. We briefly mention genetic algorithms, neural networks, Kalman filters and fuzzy logic. Thereafter, we zoom in, as an in-depth example, on the multi-decadal development and application of the lake ecosystem model PCLake and related models (PCLake Metamodel, Lake Shira Model, IPH-TRIM3D-PCLake). In the discussion, we argue that while the historical development of each approach and model is understandable given its 'leading principle', there are many opportunities for combining approaches. We take the point of view that a single 'right' approach does not exist and should not be strived for. Instead, multiple modelling approaches, applied concurrently to a given problem, can help develop an integrative view

Background: According to the Green World Hypothesis of Hairston, Smith, and Slobodkin,all plants are edible for some herbivores. Hence, the copious abundance of plant biomass,typical for terrestrial ecosystems, depends on the collective regulatory action of predators on the herbivore guild. According to the counterarguments of Polis and Strong, the defensive traits of terrestrial plants attenuate terrestrial trophic cascades to species-specific trickles,so elimination of predators might lead to increased abundance of inedible plants but will not influence community-level plant biomass. Question: Does the elimination of predators from a low arctic scrubland, with high-quality forage plants and poorly edible evergreen ericoids, lead to a reduction of community-level plant biomass or to an increased abundance of well-defended evergreen ericoids? Methods: In 1991, we introduced grey-sided voles (Myodes rufocanus) to islands, initially harbouring dense scrubland vegetation, and established permanent plots there. In 2000, we transplanted vegetation blocks from a large three-trophic-level island with voles and predators,to two-trophic-level islands with introduced voles but without resident predators, and also to vole-free one-trophic-level islands, and back to the three-trophic-level island. Vole densities were monitored by semi-annual live trapping. Vegetation was monitored by the point-frequency method. Results: In the absence of predators, vole densities increased 3.7-fold and the communitylevel plant biomass was decimated. The least palatable plant group, evergreen ericoids,suffered especially heavily, whereas palatable herbaceous plants increased in abundance. However, all three functional plant groups responded positively to the elimination of grey-sided voles. Conclusions: Our results corroborate the Green World Hypothesis, indicating that in the absence of predators, plant defences do not prevent runaway consumption of the vegetation.

Background: According to the Green World Hypothesis of Hairston, Smith, and Slobodkin, all plants are edible for some herbivores. Hence, the copious abundance of plant biomass, typical for terrestrial ecosystems, depends on the collective regulatory action of predators on the herbivore guild. According to the counterarguments of Polis and Strong, the defensive traits of terrestrial plants attenuate terrestrial trophic cascades to species-specific trickles, so elimination of predators might lead to increased abundance of inedible plants but will not influence community-level plant biomass. Question: Does the elimination of predators from a low arctic scrubland, with high-quality forage plants and poorly edible evergreen ericoids, lead to a reduction of community-level plant biomass or to an increased abundance of well-defended evergreen ericoids? Methods: In 1991, we introduced grey-sided voles (Myodes rufocanus) to islands, initially harbouring dense scrubland vegetation, and established permanent plots there. In 2000, we transplanted vegetation blocks from a large three-trophic-level island with voles and predators, to two-trophic-level islands with introduced voles but without resident predators, and also to vole-free one-trophic-level islands, and back to the three-trophic-level island. Vole densities were monitored by semi-annual live trapping. Vegetation was monitored by the point-frequency method. Results: In the absence of predators, vole densities increased 3.7-fold and the communitylevel plant biomass was decimated. The least palatable plant group, evergreen ericoids, suffered especially heavily, whereas palatable herbaceous plants increased in abundance. However, all three functional plant groups responded positively to the elimination of grey-sided voles. Conclusions: Our results corroborate Green World Hypothesis, indicating that in the absence of predators, plant defences do not prevent runaway consumption of the vegetation. The fate of plants in predat

Food web complexity is thought to weaken the strength of terrestrial trophic cascades whereby strong natural enemy impacts on herbivores cascade to indirectly influence primary production. Predator diversity can enhance food web complexity by promoting the occurrence of intraguild predation, wherein predators feed on each other and on shared prey. In such cases, theory suggests that the impact of predation on herbivores relaxes and cascading effects on basal resources are dampened. In a terrestrial marsh community, I compared arthropod predator impacts on herbivores and plant productivity between a simple food web with a single predator species and a complex food web with a diverse predator assemblage. I found that enhancing predator diversity dampened enemy effects on herbivores and weakened trophic cascades. The role of intraguild predators in dampening such trophic cascades was determined by factorially manipulating predator species richness (1, 2, or 3 species) and predator trophic composition (strict predators, intraguild predators, or a mixture of both) and measuring their effects on prey suppression and plant productivity. I found that the impact of predator richness on the strength of trophic cascades was dependent on the trophic composition of the predator complex present. Specifically, strict predators additively enhanced planthopper suppression and increased plant productivity with an increase in species richness. However, intraguild predators interacted antagonistically, resulting in greater herbivore abundance and lower plant productivity at the highest levels of species richness. An investigation of the influence of habitat complexity on cascading predator effects revealed that complex habitats with cordgrass leaf litter provided a refuge for predators from intraguild predation and elevated planthopper suppression by the diverse predator assemblage. However, reducing the antagonistic predator-predator interactions and increasing prey suppression did no

The objective of this thesis was to investigate the effects of mammalian grazers, such as microtine rodents and reindeer, (top-down effects) and nutrient availability (bottom- up effects) on the plant community of a tundra heath. I conducted a large-scale fertilization experiment and studied the impact of grazers using exclosures. I measured the effects of fertilization and grazing on soil microbial activity and nutrient cycling. I investigated the responses to fertilization of the invertebrate community, I studied the effects on the quality of bilberry as food for mammalian herbivores, and I looked at how concentrations of nutrients and carbon-based secondary defences against herbivory fluctuated between seasons in unfertilized and fertilized treatments. The results of my thesis show that the plant community investigated is exposed to a strong top-down control by mammalian herbivores. On the fertilized and grazed areas the aboveground biomass of the vascular plant community did not increase compared to unfertilized areas. However, the productivity of the plant community was clearly nutrient- limited. During the eight years of the experiment, on the fertilized areas plant biomass was significantly increased inside the herbivore exclosures In my study mammalian herbivores at comparatively low densities and grazing outside the growing season were sufficient to control the biomass of a heterogeneous plant community. Microtine rodents (Norwegian lemmings and grey-sided voles) preferred the fertilized areas for overwintering. The food plant quality of bilberry for grey-sided voles was improved on the fertilized areas throughout the year. Grazing decreased the nitrogen storage in the aboveground plant biomass. Reindeer and rodents had also important indirect effects on the plant community by decelerating soil nutrient cycling and soil microbial activity. This effect may be accelerated by the impact of herbivore on plant species composition. Graminoids, which contained the, Diss. (sammanfattning) Umeå : Umeå universitet, 2001, härtill 6 uppsstser., digitalisering@umu