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Compte, Ciurana Jordi. "Food webs of Mediterranean coastal wetlands". Doctoral thesis, Universitat de Girona, 2010. http://hdl.handle.net/10803/7879.
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En aquesta tesi doctoral s'han estudiat els efectes directes i indirectes de dos tipus d'espècies claus de la comunitat aquàtica dels aiguamolls de l'Empordà (aiguamolls costaners mediterranis amb una xarxa tròfica senzilla). S'han realitzat experiments al camp utilitzant microcosmos i mesocosmos i els resultats han estat analitzats mitjançant tres aproximacions: la taxonòmica, la funcional i la de mides. S'ha comprovat que en situacions amb absència de predadors i dominància d'una única espècie en el zooplàncton (en aquest cas Calanipeda aquaedulcis i Daphnia magna), la segregació del recurs entre els diferents estadis de desenvolupament de la mateixa espècie zooplanctònica és una estratègia per evitar la competència intraespecífica en condicions de limitació de recurs. Per altra banda, la presència de diferents top-predators a la comunitat aquàtica (en aquest cas la medusa Odessia maeotica i el peix Aphanius iberus) desencadena una cascada tròfica en el plàncton però amb efectes top-down diferents segons el top-predator.In this PhD, direct and indirect effects of key species were studied in the aquatic community of the Empordà wetlands (Mediterranean coastal wetlands with a simple food web). Different field experiments were carried out using microcosms and mesocosms. To analyze the results, three approaches were used: taxonomic, functional and size-based. Results obtained from the experiments confirm that, in situation with absence of predator and dominance of single zooplanktonic specie (in this case Calanipeda aquaedulcis and Daphnia magna), resource partitioning among different developmental stages of same zooplanktonic specie is a strategy to reduce the intraespecific competence when the resource is limiting. On the other hand, the presence of different top-predators in aquatic community (in this case the jellyfish Odessia maeotica and the Iberian toothcarp Aphanius iberus) triggers a trophic cascade in plankton, however they have different top-down effects according to top-predator.
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Vander, Zanden M. Jake. "Trophic position in aquatic food webs". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/NQ55390.pdf.
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Chasnoff, Beth. "Food webs of the Cosumnes River, CA /". For electronic version search Digital dissertations database. Restricted to UC campuses. Access is free to UC campus dissertations, 2005. http://uclibs.org/PID/11984.
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Gudmundson, Sara. "Stabilizing factors in spatially structured food webs". Thesis, Linköping University, Linköping University, Theoretical Biology, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-18657.
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Ecological models have problems showing the positive relationship between diversity and stability found in nature. Theory states that complex food webs have high extinction risks and low stability. However, persistent food webs found in nature are large and complex containing many interconnections between species. There are many possible mechanisms enabling persistent food webs such as; complex interaction patterns, asynchronous fluctuations of species densities, environmental fluctuations and spatial distribution. These factors have not been used in classical models. In this study, coloured environmental 1/f noise and dispersal between subpopulations were incorporated into a diamond shaped food web based on a model by Vasseur and Fox 2007. Contradictions between theoretical and empirical results regarding food webs can be resolved by detailed analyses of models, withholding stabilizing mechanisms. Weak environmental 1/f noise generated an increased coefficient of stability but the stabilizing effect of noise can be questioned because of a decreased mean food web biomass and reduced stabilizing effect when reddened. However, detailed studies of the food web revealed that noise can redistribute density proportions between species, evading lowest species density and thereby increase food web resistance to demographic stochasticity and catastrophes. Noise induced density proportion shifts imply that large population sizes are no insurance towards future increase in environmental variance. Synchrony of species environmental responses and dispersal between subpopulations can both have major influences on stability and extinction risk of smaller food webs indicating that spatial structure could be one of the dominating factors stabilizing complex food webs found in nature.
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Teng, Jack 1979. "Structure and energetics in theoretical food webs". Thesis, McGill University, 2003. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=80884.
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This thesis studies how structure and energetics influence complex food web dynamics. In Chapter 1, I approach the question by studying a simple food web model that can be modified to include different structural and energetic features. In Chapter 2, I study stability and food web properties in assembled webs that are structured by body-size restrictions and a generalist-specialist tradeoff. The results of both chapters suggest that structure and energetics must be considered to understand food web dynamics. In Chapter 1, I find that food web structure can be modified by weak and strong energetic flows and stabilize dynamics through asynchrony. In Chapter 2, I find that food web assembly with different assemblages of generalists or specialists leads to structures that have corresponding differences in the stability and properties of food webs. Hence, my thesis reexamines the relationship of complexity and dynamics from a topological and energetic framework.
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McQuaid, Christopher Finn. "Complex food webs : the role of parasites". Thesis, University of Bath, 2014. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.648943.
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Parasites are vital aspects of an ecosystem, and yet have only recently begun to be included in theoretical studies of food webs. There are numerous reasons for this neglect, but recent interest has arisen in remedying the situation. Key to the addition of parasites are various structural features that ecological networks display, and the mechanisms behind them. We look at two of these features, nestedness and downward asymmetry, and describe mathematically the forces that create them. We discover from the basic reproductive ratio that population dynamics are insufficient to drive nested and anti-nested patterns in host-parasite networks, and instead we demonstrate the manner in which adaptive dynamics may be used to explain patterns through the coevolution of species interaction traits. We use the same technique in a mutualistic network in order to compare results. Following this, we use the basic reproductive ratio to demonstrate how the population dynamics of infectious systems promote the presence of trophic parasites in particular interaction motifs, and discuss the implications of the addition of parasites to the stability of ecological networks as a whole. In summary, we demonstrate that the optimal use of resources by species in order to promote population growth results in two important structural patterns of host-parasite networks. Insights gained from this motivate us to investigate the importance of parasites on models of food web dynamics, and in particular, their stability.
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Read, Daniel Steven. "Molecular analysis of subterranean detritivore food webs". Thesis, Cardiff University, 2007. http://orca.cf.ac.uk/55689/.
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Insect- and mollusc-parasitic nematodes are widely used for the biological control of soil-dwelling pests. Despite being used successfully to control a broad range of pest species in a variety of different crops, there have been many examples of pest control failures. Although the abiotic factors that influence the short-term persistence of nematodes are well understood, there is a lack of knowledge about the biotic factors. PCR-probes were designed and tested for the detection of three species of mollusc- and insect-parasitic nematodes: Phasmarhabditis hermaphrodita, Heterorhabditis megidis and Steinernema feltiae. These probes were used successfully to amplify nematode DNA from the gut of microarthropod predators. Potential sources of error and variation in prey detection times were tested and quantified, including nematode phoresy, scavenging, changes in temperature and predator body size. Field trials and molecular screening were used to identify predators of nematodes in the field, including the surface-dwelling collembola Isotoma viridis and Isotomurus palustris. Positive numerical responses by the surface-dwelling collembola indicated that immigration into nematode-sprayed (and hence food-rich) habitats was occurring. Terminal Restriction Fragment Length Polymorphism (T-RFLP) was tested for monitoring the effects of nematode biopesticide application on soil-dwelling nematode abundance and community structure. Using this technique, it was possible to create a nematode 'community profile'. Furthermore, it was possible, using T-RFLP, to identify changes in the nematode community after the application P. hermaphrodita to the soil. The nematode-specific PCR primers were used in conjunction with primers designed to amplify DNA from mollusc and insect hosts, including Deroceras reticulatum, Tenebrio molitor and Steinernema feltiae. Using these primers, it was possible to detect nematode parasitism within the host and intraguild predation by the carabid Pterostichus melanarius on infected hosts. Choice-test feeding trials with P. melanarius were used to investigate the production of antifeedants by the nematode-bacterium complex within the host are widely used for the biological control of soil-dwelling pests. Despite being used successfully to control a broad range of pest species in a variety of different crops, there have been many examples of pest control failures. Although the abiotic factors that influence the short-term persistence of nematodes are well understood, there is a lack of knowledge about the biotic factors. PCR-probes were designed and tested for the detection of three species of mollusc- and insect-parasitic nematodes: Phasmarhabditis hermaphrodita, Heterorhabditis megidis and Steinernema feltiae. These probes were used successfully to amplify nematode DNA from the gut of microarthropod predators. Potential sources of error and variation in prey detection times were tested and quantified, including nematode phoresy, scavenging, changes in temperature and predator body size. Field trials and molecular screening were used to identify predators of nematodes in the field, including the surface-dwelling collembola Isotoma viridis and Isotomurus palustris. Positive numerical responses by the surface-dwelling collembola indicated that immigration into nematode-sprayed (and hence food-rich) habitats was occurring. Terminal Restriction Fragment Length Polymorphism (T-RFLP) was tested for monitoring the effects of nematode biopesticide application on soil-dwelling nematode abundance and community structure. Using this technique, it was possible to create a nematode 'community profile'. Furthermore, it was possible, using T-RFLP, to identify changes in the nematode community after the application P. hermaphrodita to the soil. The nematode-specific PCR primers were used in conjunction with primers designed to amplify DNA from mollusc and insect hosts, including Deroceras reticulatum, Tenebrio molitor and Steinernema feltiae. Using these primers, it was possible to detect nematode parasitism within the host and intraguild predation by the carabid Pterostichus melanarius on infected hosts. Choice-test feeding trials with P. melanarius were used to investigate the production of antifeedants by the nematode-bacterium complex within the host.
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Wootton, Louise Sarah. "Salt-flocculated organic matherial as a food source in estuarine food webs". Thesis, University of British Columbia, 1989. http://hdl.handle.net/2429/27750.
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Large amounts of particulate material were found to flocculate from water collected from local, organic rich streams upon addition of salt water. This material was found to compose approximately 50% humic substances and to have a C:N ratio of about 50:1. Feeding studies using floe having various degrees of bacterial colonisation showed that bacterial abundance was an important determinant of the palatability of this material to the copepod grazer, Tigriopus californicus. Palatability of flocculant particles increased linearly with increasing bacterial abundances in the range of 0-10⁶ cells • mL⁻¹, while increases in bacterial abundances above this concentration resulted in lower than expected grazing rates. Further inoculations with single strains of bacteria isolated from the floe showed that this increased palatability occurred with only certain components of the floe fauna. Ingestion of floe colonised by a "normal" bacterial fauna was found to be beneficial for the survival of Cl and adult stages of Tigriopus and was found to sustain egg production of inseminated females. The presence of floe did not, however, result in the improved survival of the earlier naupliar stages of Tigriopus. Mass spectrometric analyses suggest that significant amounts of carbon are assimilated from floe made from water collected during the winter months. As floe is ingested at very low rates in the absence of colonising microbes, benefit from the ingestion of floe is postulated to result from the conversion of floe carbon into microbial biomass and the subsequent assimilation of those microbes by the copepod grazer. The fact that few differences exist between the IR-spectra of floe food and the faecal material derived from copepods fed a floe diet suggests that little change is undergone by the bulk of the organic matrix during ingestion and passage through the copepod gut. Ingestion of floe may therefore work to protect the flocculant material from subsequent microbial degradation by compacting the material into pellets which will be rapidly delivered to the sediments as a result of high sinking rates. Feeding studies with a variety of species collected from local coastal waters suggest that a wide spectrum of organisms may ingest flocculant material when that material is present in their environs. As flocculant material is primarily produced in the winter, a time when estuarine primary productivity is low, floe is postulated to play an important role in sustaining these organisms through periods of low food availability.Science, Faculty of
Earth, Ocean and Atmospheric Sciences, Department of
Graduate
9
Drakare, Stina. "The Role of Picophytoplankton in Lake Food Webs". Doctoral thesis, Uppsala University, Limnology, 2002. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-2710.
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Picophytoplankton were inferior competitors for inorganic phosphorus compared to heterotrophic bacteria. This may be due to the source of energy available for the heterotrophs, while cell-size was of minor importance. However, picophytoplankton were superior to large phytoplankton in the competition for nutrients at low concentrations.
Biomass of picophytoplankton was low in brownwater lakes and high in clearwater lakes, compared to the biomass of heterotrophic bacteria. The results suggest that picophytoplankton are inferior to heterotrophic bacteria in the competition for inorganic nutrients in brownwater lakes, where the production of heterotrophic bacteria is subsidized by humic dissolved organic carbon (DOC)
Relative to large phytoplankton, picophytoplankton were most important in lakes with intermediate water colour, despite the fact that the lowest nutrient concentrations were found in the clearwater lakes. Large phytoplankton in the clearwater lakes may be able to overcome nutrient competition with picophytoplankton by vertical migration.
In conclusion, changes in nutrient content, light availability and concentrations of DOC affect the interactions of heterotrophic bacteria, picophytoplankton and large phytoplankton and are therefore important factors for the structure of the food web in the pelagic zones of lakes.
Picophytoplankton (planktonic algae and cyanobacteria, < 2 µm) constitute an important component of pelagic food webs. They are linked to larger phytoplankton and heterotrophic bacteria through complex interactions including competition, commensalism and predation. In this thesis, field and laboratory studies on the competitive ability of picophytoplankton are reported.
10
Borrvall, Charlotte. "Biodiversity and Species Extinctions in Model Food Webs". Doctoral thesis, Linköping : Department of Physics, Chemistry and Biology, Linköping University, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-6660.
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Chaneton, Enrique Jose. "Herbivore-mediated plant interactions in grassland food webs". Thesis, Imperial College London, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.314368.
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Weissbach, Astrid. "The role of allelopathy in microbial food webs". Doctoral thesis, Linnéuniversitetet, Institutionen för naturvetenskap, NV, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-11375.
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Phytoplankton produce allelochemicals; excreted chemical substances that are affecting other microorganisms in their direct environment. In my thesis, I investigated strain specific variability in the expression of allelochemicals of the harmful flagellate Prymnesium parvum, that is euryhaline but mainly bloom forming in brackish water. I found a large variation among strains, but further showed that all strains of P. parvum were more allelopathic in brackish water compared to marine water. In a marine microbial community, allelochemicals can affect prey, competitors and grazers both, directly and indirectly. For instance, in a food web where grazing controls prey abundance, the negative direct effect of allelochemicals on grazers will positive affect their prey. During my thesis, I investigated how marine microbial communities respond to the addition of allelochemicals. I performed field experiments with microbial communities from seawater collected from different places over Europe, and tested how this communities respond to the addition of allelochemicals from the dinoflagellate Alexandrium tamarense. Before I incubated the microbial communities for several days with A. tamarense algal filtrate, I evaluated the allelopathic efficiency of the algal filtrates with an algal monoculture of Rhodomonas spp. This allowed me to compare the effect of A. tamarense filtrate between the different microbial communities. In general, bacteria reached higher abundances when allelochemicals were present. As allelochemicals also inhibited nanoflagellates and ciliates, we concluded, that allelochemicals indirectly benefit bacteria by reducing grazing pressure. In microbial food webs with many heterotrophic grazers, allelochemicals further benefitted other phytoplankton by inhibiting grazers. It was also shown that bioavailable DOM is released from a microbial community when allelochemicals are present. As most DOM was released from the seawater fraction > 60 μm, we concluded, that larger microorganisms are more affected by allelochemicals than smaller microorganisms. The results can be explained by the surface to volume ratio of microorganisms: Larger organisms provide more contact surface for allelochemicals, and therefore, are probably more vulnerable towards allelochemicals. In conclusion, the effect of allelochemicals on a microbial community depends among others on the structure of the microbial food web, the amount of available DOM, the particle density in the seawater and the composition of the phytoplankton community.
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Landrum, Jason Paul. "Movement of new nitrogen through oceanic food webs". Diss., Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/28151.
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Thesis (M. S.)--Biology, Georgia Institute of Technology, 2009.Committee Chair: Joseph Montoya; Committee Member: Ellery Ingall; Committee Member: Emanuele DiLorenzo; Committee Member: Marc Weissburg; Committee Member: Mark Hay.
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Eklöf, Anna. "Species extinctions in food webs : local and regional processes". Doctoral thesis, Linköpings universitet, Teoretisk Biologi, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-51815.
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Loss of biodiversity is one of the most severe threats to the ecosystems of the world. The major causes behind the high population and species extinction rates are anthropogenic activities such as overharvesting of natural populations, pollution, climate change and destruction and fragmentation of natural habitats. There is an urgent need of understanding how these species losses affect the ecological structure and functioning of our ecosystems. Ecological communities exist in a landscape but the spatial aspects of community dynamics have until recently to large extent been ignored. However, the community’s response to species losses is likely to depend on both the structure of the local community as well as its interactions with surrounding communities. Also the characteristics of the species going extinct do affect how the community can cope with species loss. The overall goal of the present work has been to investigate how both local and regional processes affect ecosystem stability, in the context of preserved biodiversity and maintained ecosystem functioning. The focus is particularly on how these processes effects ecosystem’s response to species loss. To accomplish this goal I have formulated and analyzed mathematical models of ecological communities. We start by analyzing the local processes (Paper I and II) and continue by adding the regional processes (Paper III, IV and V). In Paper I we analyze dynamical models of ecological communities of different complexity (connectance) to investigate how the structure of the communities affects their resistance to species loss. We also investigate how the resistance is affected by the characteristics, like trophic level and connectivity, of the initially lost species. We find that complex communities are more resistant to species loss than simple communities. The loss of species at low trophic levels and/or with high connectivity (many links to other species) triggers, on average, the highest number of secondary extinctions. We also investigate the structure of the post-extinction community. Moreover, we compare our dynamical analysis with results from topological analysis to evaluate the importance of incorporating dynamics when assessing the risk and extent of cascading extinctions. The characteristics of a species, like its trophic position and connectivity (number of ingoing and outgoing trophic links) will affect the consequences of its loss as well as its own vulnerability to secondary extinction. In Paper II we characterize the species according to their trophic/ecological uniqueness, a new measure of species characteristic we develop in this paper. A species that has no prey or predators in common with any other species in the community will have a high tropic uniqueness. Here we examine the effect of secondary extinctions on an ecological community’s trophic diversity, the range of different trophic roles played by the species in a community. We find that secondary extinctions cause loss of trophic diversity greater than expected from chance. This occurs because more tropically unique species are more vulnerable to secondary extinctions. In Paper III, IV and V we expand the analysis to also include the spatial dimension. Paper III is a book chapter discussing spatial aspects of food webs. In Paper IV we analyze how metacommunities (a set of local communities in the landscape connected by species dispersal) respond to species loss and how this response is affected by the structure of the local communities and the number of patches in the metacommunity. We find that the inclusion of space reduces the risk of global and local extinctions and that lowly connected communities are more sensitive to species loss. In Paper V we investigate how the trophic structure of the local communities, the spatial structure of the landscape and the dispersal patterns of species affect the risk of local extinctions in the metacommunity. We find that the pattern of dispersal can have large effects on local diversity. Dispersal rate as well as dispersal distance are important: low dispersal rates and localized dispersal decrease the risk of local and global extinctions while high dispersal rates and global dispersal increase the risk. We also show that the structure of the local communities plays a significant role for the effects of dispersal on the dynamics of the metacommunity. The species that are most affected by the introduction of the spatial dimension are the top predators.
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Zheng, David W. "Theoretical studies linking soil food webs and ecosystem processes /". Uppsala : Swedish Univ. of Agricultural Sciences (Sveriges lantbruksuniv.), 1998. http://epsilon.slu.se/avh/1998/91-576-5347-X.gif.
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Lamb, Philip. "Resolving the role of jellyfish in marine food webs". Thesis, University of East Anglia, 2018. https://ueaeprints.uea.ac.uk/69971/.
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Jellyfish populations in the Irish Sea have been increasing. This has caused a variety of economic problems, such as the destruction of aquaculture installations, and new opportunities, such as the establishment of a jellyfish fishery. However, interactions between jellyfish and other biota in the ecosystem is poorly characterised and ecological consequences of an increasing jellyfish population remains unknown. Molecular gut content analysis methodologies were developed to address this data gap. Cnidarian specific primers were developed and showed using more than 2500 stomachs that, during February and March, moon and mauve-stinger jellyfish were consumed by common fish species including herring, whiting, and lesser-spotted dogfish. Revisiting the ecosystem in October with 375 additional samples, the primers indicated jellyfish predation varied temporally: small jellyfish were still targeted by mackerel, however moon jellyfish adults were not preyed upon. To understand the context in which jellyfish consumption occurred a high throughput sequencing (HTS) approach using two universal primers was developed. A meta-analysis of HTS studies suggested results contained a quantitative signal, and the methodology could be used to move beyond a presence/absence approach. Using 188 samples from nine fish species, it was shown that jellyfish were consumed as part of a generalised diet during summer months. Finally, the approaches used to model jellyfish in the ecosystem model Ecopath with Ecosim (EwE) were reviewed. Jellyfish were included more frequently over time, however approaches remained relatively crude in the absence of high quality data in many ecosystems. Together, these approaches have gone some way towards addressing the data gap: jellyfish interactions with other biota have been recorded, and new approaches for studying these interactions have been developed. This has established a baseline for novel research opportunities such as mechanistic modelling of jellyfish, exploration of quantitative HTS approaches, and the generation of dietary time-series data to be conducted.
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Nielsen, Jens Munk. "Species interactions and energy transfer in aquatic food webs". Doctoral thesis, Stockholms universitet, Institutionen för ekologi, miljö och botanik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-123600.
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Food webs are structured by intricate nodes of species interactions which govern the flow of organic matter in natural systems. Despite being long recognized as a key component in ecology, estimation of food web functioning is still challenging due to the difficulty in accurately measuring species interactions within a food web. Novel tracing methods that estimate species diet uptake and trophic position are therefore needed for assessing food web dynamics. The focus of this thesis is the use of compound specific nitrogen and carbon stable isotopes and molecular techniques for assessing predator-prey interactions and energy flow in natural aquatic ecosystems, with a particular focus on the species links between phytoplankton and zooplankton. The use of δ15N amino acid values to predict organism trophic position are evaluated through a meta-analysis of available literature which included measurements from 359 marine species (article I). Through a controlled feeding study isotope incorporation in aquatic organisms, across both plant-animal and animal-animal species linkages is further assessed (article II). These studies showed that δ15N amino acid values are useful tools for categorizing animal trophic position. Organism feeding ecology influenced nitrogen trophic discrimination (difference in isotope ratio between consumer and diet), with higher discrimination in herbivores compared to omnivores and carnivores (article I). Nitrogen isotope trophic discrimination also varied among feeding treatments in the laboratory study (article II). The combined findings from articles I & II suggest that researchers should consider using group specific nitrogen trophic discrimination values to improve accuracy in species trophic position predictions. Another key finding in the controlled laboratory study (article II) was consistently low carbon isotope discrimination in essential amino acids across all species linkages, confirming that these compounds are reliable dietary tracers. The δ13C ratios of essential amino acids were applied to study seasonal dynamics in zooplankton resource use in the Baltic Sea (article III). Data from this study indicated that zooplankton assimilate variable resources throughout the growing season. Molecular diet analysis (article IV) showed that marine copepod and cladoceran species ingested both autotrophic and heterotrophic resources. Evidence from both articles III & IV also revealed that zooplankton feed on a relatively broad range of diet items but not opportunistically on all available food sources. Mesozooplankton feeding patterns suggested that energy and nutritional flows were channelled through an omnivorous zooplankton food web including microzooplankton prey items. Overall the results of this thesis highlight that stable isotope ratios in specific compounds and molecular techniques are useful tracing approaches that improve our understanding of food web functioning.At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 4: Manuscript.
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Landström, Emelie. "Resource use by macroinvertebrates within boreal stream food webs". Thesis, Umeå universitet, Institutionen för ekologi, miljö och geovetenskap, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-105593.
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Stream food webs are supported by carbon produced within the stream (autochthonous) and from terrestrial environments (allochthonous). Allochthonous carbon (C) inputs are assumed to be the dominant C source supporting food webs within small streams, but few direct estimates of resource use in small streams have been made, especially in boreal streams. The objective of this study was to determine the relative dependence on allochthonous and autochthonous C by consumers in relation to C pools within streams with high terrestrial inputs. Furthermore, this study aimed to investigate if the relative resource use of allochthonous and autochthonous C by consumers differed among seasons (summer and fall), between streams of different sizes, and locations within the catchment. To estimate consumer resource use, δ2H signatures for organic C sources were compared to those of six key consumers in five streams of varying catchment sizes in northern Sweden. Macroinvertebrate biomass was quantified to calculate a taxa-specific biomass-weighted allochthony, and compared with the mass of different C pools potentially available for consumers. The biomass-weighted mean allochthony for all samplings ranged between 43.5-61.5%; there was thus high autochthonous support despite low algal density and high terrestrial C pools within the streams. No significant trend in allochthony was observed over season (linear regression, p-value >0.05). Allochthony differed by invertebrate taxa and was not related to stream size or location in catchment. These results suggest that autochthonous C is far more important for consumers in boreal streams than previously recognized.
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Sabino, Magali. "Bioaccumulation of trace elements in Seychelles marine food webs". Thesis, La Rochelle, 2021. http://www.theses.fr/2021LAROS026.
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La sécurité alimentaire, qui est la garantie de l’approvisionnement et de la qualité des aliments tout en gérant les ressources de manière durable, est intrinsèquement liée à la connaissance de la biologie et l’écologie des espèces consommées. Dans un contexte de dérèglement climatique menaçant la salubrité des produits de la mer, il est donc nécessaire d’établir un référentiel sur le fonctionnement des systèmes marins, ainsi que sur l’occurrence des nutriments et des contaminants dans les produits de la mer. C’est d’autant plus important pour les Petits Etats Insulaires en Développement (PEID), qui dépendent des ressources marines pour leur subsistance, et où les produits de la pêche sont la première source de protéines et micronutriments (éléments traces essentiels) pour les populations locales. Malgré l’importance des systèmes tropicaux pour la sécurité alimentaire, ces systèmes sont peu étudiés comparés aux systèmes polaires et tempérés. Cette thèse vise à mieux comprendre le fonctionnement des systèmes marins tropicaux, et à établir un référentiel sur l’occurrence des micronutriments et des contaminants métalliques dans les produits de la pêche aux Seychelles (Océan Indien), un PEID tropical. En étudiant les concentrations en éléments traces aux niveaux inter- et intraspécifique, nous avons identifié différents facteurs intrinsèques et extrinsèques influençant la bioaccumulation de ces éléments dans les ressources marines tropicales. Nous avons aussi montré l’importance de considérer différentes échelles (individu, espèce et écosystème) pour mieux comprendre l’occurrence des éléments traces essentiels et non-essentiels dans les produits de la merFood security, that is guarantying food supply and quality while sustainably managing resources, is closely linked to knowing the biology and ecology of consumed species. In a context of global changes that are threatening seafood safety, it is thus necessary to establish baselines on marine ecosystem functioning, as well as nutrient availability and contamination occurrence in seafood. This is all the more important in Small Island Developing States (SIDS), where populations rely on marine resources for their subsistence, and where capture fisheries resources are the main sources of proteins and micronutrients (i.e. essential trace elements) in local populations’ diet. In spite of the importance of tropical systems in ensuring food security, they remain largely understudied compared to polar and temperate systems. This thesis thus aims to better understand the functioning of tropical marine systems, and to establish a baseline on micronutrient availability and metal(loid) contamination in a wide diversity of capture fisheries resources from the Seychelles (Western Indian Ocean), a tropical SIDS. By investigating trace element concentration patterns at the inter- and intraspecific levels, it was possible to identify intrinsic and extrinsic factors influencing trace element bioaccumulation in tropical capture fisheries resources. We thus highlighted the importance of considering different scales (individual, species, and ecosystem) to better understand essential trace element availability and non-essential trace element occurrence in seafood
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Marshall, Melanie M. "Interactive effects of wastewater effluent on stream food webs". Bowling Green State University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1563457844184326.
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Hamladji, Yasmina. "Efficiency of diatom and flagellate-based marine food webs". Thesis, Umeå universitet, Institutionen för ekologi, miljö och geovetenskap, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-184613.
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Aquatic microbial food webs are in general size structured. Phytoplankton, which constitute the base of the food web, are grazed by protozoa and mesozooplankton, which in turn are consumed by planktivorous fish. Food web efficiency (FWE) is a measure of how efficiently energy is transported up the food web. FWE is low if the phytoplankton is inedible by the grazers, while FWE is higher if the phytoplankton community is dominated by edible phytoplankton. Recently, the presence of microfungi in aquatic food webs have been suggested to facilitate energy transfer up the food web, via the “mycoloop”. The aim of the study was to set-up a model system of phytoplankton – zooplankton food chains, relevant to the Baltic Sea, and to test FWE in diatom and flagellate-based food webs. Further, I wanted to introduce microfungi in the system and observe their impact on FWE. After many phytoplankton and zooplankton species tests, I decided to perform grazing experiments using one grazer, the ciliate Tetrahymena pyriformis, and two phytoplankton species: a diatom (Skeletonema marinoi) and a flagellate (Rhodomonas baltica). I hypothesized that T. pyriformis would more efficiently feed on flagellates than on diatoms. I performed a grazing experiment where the increase in ciliate abundance was measured, the consumption of the phytoplankton monitored and the FWE estimated. The diatom-based food web led to 14 times higher FWE than the flagellate-based food web. The variation in FWE may be explained by a difference in initial abundances introduced in the experimental treatment, which created unequal grazer:prey ratio between treatments. Further, the swimming behaviour of the flagellate might have reduced the capture efficiency by the ciliate. Microfungi were introduce in an experiment, from a natural seawater sample, but fungal infection was not observed for any of the tested phytoplankton species. Further development is needed to test the effects of microfungi on marine FWE.
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Persson, Jonas. "Food Quality Effects on Zooplankton Growth and Energy Transfer in Pelagic Freshwater Food Webs". Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis Acta Universitatis Upsaliensis, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-7811.
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Venzon, Madelaine. "Food webs on plants the role of a generalist predator /". [S.l. : Amsterdam : s.n.] ; Universiteit van Amsterdam [Host], 2000. http://dare.uva.nl/document/82067.
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Layton, Astrid C. "Food webs: Realizing biological inspiration for sustainable industrial resource networks". Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/54307.
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This thesis considers the problem of how to design an industrial network to reduce cost, increase efficiency, and reduce environmental burdens. A recent approach is further developed that uses analogies with biological food webs to guide industry design. Studying ecological food webs shows that among the metrics in use, critical quantities of interest for industry design include the internal cycling of energy, the ratio of producers to consumers, and the ratio of efficiency to redundancy in the network. Metrics that are calculated using flow based information are also introduced for use in industry, a significant step forward for bio-inspired network design. A comprehensive data set of proposed, operational, and failed eco-industrial parks is compiled for use with structural food web analyses. A data set of biological food webs is also assembled to calculate sustainable benchmark values used as goals for the industrial designs. This research an essential difficulty in bio-inspired design approaches by quantitatively analyzing components of food web design by reconstructing found relationships from science and engineering 1st principles, specifically using thermodynamic 1st law efficiency. Results from this work have the potential to provide industry-wide cost savings, increase efficiency, and reduce environmental burdens through a reduction in raw material consumption and waste disposal. The results also support the view that financial competitiveness and sustainability need not be mutually exclusive: using food web network patterns embodying both economically and environmentally desirable properties, biologically redesigned industrial networks can ease both environmental and economic burdens.
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Cross, Adam D. P. "The influence of seabird-derived nutrients on island food-webs". Thesis, University of Glasgow, 2014. http://theses.gla.ac.uk/6312/.
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There is an increasing understanding of the influence seabirds have on island food webs globally, which often arises from the trans-boundary input of nutrients. Seabird-derived nutrients, primarily in the form of guano, can have significant effects on island communities by increasing primary productivity and then indirectly influencing other species. However, there are few studies looking at how the influence of seabirds permeates island food webs to higher trophic levels, in particular within the United Kingdom, which holds globally significant populations of seabirds. To understand the extent to which seabirds influence islands, the size of the seabird population must be first reliably determined. With an increasing seabird population size and density the effects of seabirds on land increases concomitantly. The Atlantic puffin Fratercula arctica is a difficult species to reliably monitor, given its underground presence from the use of burrows and its notoriously erratic attendance at colonies. This study looks firstly at a novel method to monitor the Atlantic puffin using time-lapse photography. Time-lapse photography provides a way to derive an estimate of population size from counts of individuals, by repeated photographs across a period of time with relatively low cost and from areas normally considered inaccessible. The results showed there was a significant and positive relationship between the maximum numbers of Atlantic puffins observed and the size of the population; further work is required though to reduce the error associated with population size estimates. Data from high temporal resolution time-lapse photography shows how the attendance of Atlantic puffins at the colony varies over different temporal scales. Given the variability in sampling intensity the study stresses the need for standardised sampling intensity with the use of photography to monitor Atlantic puffins. Secondly, this study showed how the presence of two seabird species, the Atlantic puffin and the great skua Stercorarius skua, alters island food webs. These seabird species are likely to change plant community diversity, relative to areas without seabirds. The chemical concentration of grasses inside seabird colonies was also altered: grasses had significantly higher concentrations of nitrogen and also had higher values of δ15N, relative to areas without seabirds. These chemical alterations suggest that nutrients from seabirds are incorporated into local vegetation. Furthermore, samples of hair from rabbits and sheep found within puffin colonies also had significantly higher values of δ15N, suggesting that nutrients travel from seabirds into secondary consumers, via ornithogenic forage. An additional study on the transfer of nutrients within island food webs showed how ornithogenic nutrients deposited on an island in the Baltic Sea were incorporated into house martins, via aquatic insects. These studies, along with an understanding of seabird population size, suggest that the impact of seabirds on island food webs may be considerable and have large consequences for island conservation and management.
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Eriksson, Björn. "Diversity of ecosystems : Variation in network structure among food webs". Thesis, Linköpings universitet, Biologi, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-130467.
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Biodiversity loss is one of the major threats to humanity. This has led to an increasing amount of research on biodiversity on genetic and species levels. Studies of diversity at the ecosystem level has however been neglected. An important aspect of ecosystems is food webs that describe the predation-prey interactions between species. Properties explaining the topological structure of food webs can be used to compare and highlight differences between ecosystems. In the present study, topological network properties are used to compare the diversity of network structures between groups of empirical food webs. Differences between 45 aquatic and 45 terrestrial food webs are compared as well as the effects of species richness on lake network structure diversity. Network structure diversity is measured as the average Euclidean distance from food webs to their group centroid in a multidimensional space of network properties. While the average network structure differs between aquatic and terrestrial food webs, no significant difference in variation is found. For 128 Swedish and 48 North American lake food webs, increasing species richness is shown to decrease network structure diversity. A higher diversity of network structures could potentially indicate a more ways to cope with disturbances or provisions of a higher variety of ecosystem services. Preliminary tests of ecosystem diversity effects on stability were conducted but proved inconclusive.
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O'Mara, Kaitlyn M. "The Effects of Floods on Estuarine Fisheries and Food Webs". Thesis, Griffith University, 2020. http://hdl.handle.net/10072/391521.
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Floods are extreme events that can rapidly alter water and habitat quality in receiving estuaries. Because floods are unpredictable, they are more difficult to study, so have received less research attention than freshwater flow studies, resulting in a paucity of information on their ecological effects in the coastal zone. Previous studies have shown correlations between high flow periods and increased fisheries catches, which suggests that floods stimulate productivity in receiving waters. However, there have been no studies providing direct links between floods and increased productivity responses in fisheries species. In addition, the long-term effects of deposited flood sediment on food webs in estuaries are poorly understood. Floodwaters can carry high loads of fine sediment, which settles at the most offshore portion of the estuary delta, known as a prodelta. Nutrients, trace elements and other substances are also exported from the catchment dissolved in floodwater or attached to fine sediment particles and are deposited in estuaries. However, the processes of nutrient release from suspended sediments and settled sediments, and uptake of nutrients and trace elements into the food web in receiving estuaries are not well understood. Therefore, this thesis used laboratory experiments (Chapter 2 & 3) to study these processes with the aim of gaining a better understanding of the mechanisms underpinning measured ecological flood responses using field studies (Chapter 4 & 5).
This study used catchment soils formed from three distinct rock types (granite, basalt and sandstone) from the Brisbane River (Queensland, Australia) catchment in a flood simulation experiment to quantify the rates of nutrient release during flooding (Chapter 2). In the laboratory, the fine fraction (<63 µm) of the soils was tumbled in freshwater for three days and left to settle in seawater for four weeks, and filtered water samples were taken throughout. A thin layer of the fine soils was also added to incubated sediment cores collected from central Moreton Bay, Queensland, Australia, to measure the influx or efflux of dissolved nutrients from sediments. Basalt soils, in particular, were relatively nutrient-rich and released substantial quantities of organic and inorganic dissolved nutrients, particularly phosphate. However, when soils were added to estuarine sediment cores and incubated, there was a net influx of phosphate from the overlying water. All soils continually released ammonium in both experiments, indicating that catchment soils may be an important source of ammonium to fuel productivity within the coastal zone.
Catchments can also contribute trace elements to estuaries and coastal areas. Sources of trace element (cadmium (Cd), manganese (Mn) and zinc (Zn)) accumulation in estuarine fisheries species occupying different trophic levels were determined using radioisotope experiments (Chapter 3). Clams, prawns and fish common to estuaries on the East Australian coastline were exposed to a combination of Cd, Mn and Zn in three sources: dissolved in seawater, attached to suspended sediment particles, and diet. The study showed that clams accumulated all three elements from seawater, while prawns and fish showed negligible uptake. This indicates that clams may be an important link between dissolved and bioavailable elements for higher trophic level species, since the clams bioconcentrated these elements from seawater. The suspended sediment exposures had similar outcomes, with accumulation by clams, with negligible uptake by prawns and fish. Clams may therefore be particularly sensitive to accumulation of contaminants during floods, which may be exacerbated by their sessile nature. Biokinetic modelling using moderate environmental metal concentrations showed that diet was the main source of Cd and Zn accumulation in clams, whereas seawater was likely to be the main source for clam Mn accumulation. Diet was found to be the main source of Cd, Mn and Zn accumulation in prawns and fish, which is supported by previous studies. In the diet exposures, there was also a considerable difference in assimilation efficiencies between prawns and fish. The results of this study suggest that the contribution of diet to trace element accumulation at higher tropic levels may be larger than previously thought, and diet should therefore be considered in trace element studies involving high trophic level species.
To identify short-term responses to a flood, multiple condition indices were determined for brown tiger prawns collected before and after a large cyclone-driven flood from several sites in central Moreton Bay (Chapter 4). Prawns collected from sites closest to the Brisbane River and Moreton Island showed no consistent change in condition over time. However, prawns collected from the most southern sites closest to the Logan River, which was the most severely flooded river system during the storm, responded positively to the flood with increased condition measured in terms of length-weight relationships, carbon-nitrogen ratios and muscle lipid content. Peak condition was measured on the first post-flood sampling occasion (i.e. day 11), and prawns collected 53 d after the flood were found to be in a similar condition to those before the flood. This peak in prawn condition coincided with an increase in benthic algal biomass that occurred simultaneously, measured as chlorophyll-a concentrations. Unlike previous studies, which found negative flood condition responses in fish in urban estuaries, the results from this study show that floods in South East Queensland can increase food web productivity in Moreton Bay.
Water conditions in estuaries following floods usually return to normal within a couple of months, therefore long-term flood effects are likely to be caused by catchment sediment that is deposited on the estuary prodelta. To assess catchment influences on energy flow to fish and prawns living on flood prodeltas, common fish and prawn species were analyzed for stable isotope and trace element composition (Chapter 5). Fish and prawns were collected from a prodelta in an urbanized catchment (Moreton Bay) and three non-urbanized catchments (Gulf of Carpentaria). Links between diet and trace element composition were found. Differences in trace element composition were greatest between fish and prawns, which was reflected in correlations of trace elements with nitrogen isotopes. Differences within fish and prawn groups were also found, which were correlated to carbon isotopes and reflected benthic versus pelagic diets of different species. These correlations also highlight the importance of diet in trace element accumulation, and show that trace elements can be useful in food web studies. Variations in diet between locations were measured for some species, particularly catfish, suggesting that material exported from the catchment during floods influences food webs through availability of quality prey in estuary prodeltas. Catfish in Moreton Bay were found to be feeding at a high trophic level, suggesting that the urbanization of the Brisbane River catchment does not negatively affect the quality of food available in the Brisbane River prodelta.
Overall, the results of this thesis showed that floods, and the sediments they transport to estuaries, can be beneficial for fisheries and food webs in receiving estuaries. In addition, trace element accumulation is linked to diet, and stable isotopes and trace elements can be combined to study catchment influences on estuarine food webs. An effective and transferrable methodology for mapping catchment influences and evaluating food quality in important fisheries habitats was identified. Floods facilitate a seaward transport of water, sediment and substances from catchments that are taken up into food webs in the coastal zone. Flood frequency and intensity is expected to increase with a changing climate and the work presented here fills important knowledge gaps on ecological responses to floods. While organisms have responded to and recovered from flood events throughout history, changes to sediment and water volumes through land clearing and damming of rivers may affect the quality of food, and therefore fisheries productivity, in the coastal zone. This study therefore has important implications for management of land use, erosion and water resource allocation within catchments.Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Environment and Sc
Science, Environment, Engineering and Technology
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Guo, Fen. "The Influence of Light and Nutrients on Stream Food Webs". Thesis, Griffith University, 2016. http://hdl.handle.net/10072/366591.
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While many streams and rivers are dominated by terrestrial inputs of organic carbon, algae are important trophic base for stream food webs. However, the nutritional importance of algae for stream invertebrates has only recently been highlighted. Algae are acknowledged as higher quality food compared with terrestrial organic matter for the growth and reproduction of invertebrates. In part, this is because of algal higher polyunsaturated fatty acid (PUFA) content. Current studies on algal PUFA and their effect on invertebrates are mainly from lacustrine systems, and only few studies have explicitly investigated algal PUFA in streams. This thesis aimed to evaluate the role of algal food quality, as assessed by PUFA, in stream food webs by using a range of methods literature review, field investigation, field manipulative study and laboratory feeding experiment. All experiments involved in this thesis were conducted in subtropical streams in South-East Queensland, Australia.
Riparian canopy cover and NOx-N concentrations were identified as the two most important factors affecting periphyton PUFA profiles. Periphyton eicosapentaenoic (EPA, 20:5ω-3) and docosahexaenoic (DHA, 22:6ω-3) were positively correlated with canopy cover and NOx-N concentrations, whereas α-linolenic (ALA, 18:3ω-3) and linoleic acid (LIN, 18:2ω-6) were positively correlated with NOx-N, but negatively with canopy cover. Variations in riparian canopy cover and nutrients gave rise to opposite outcomes in terms of periphyton food quality and quantity. The highest periphyton food quality occurred in streams with high canopy cover and low nutrients, while the highest periphyton food quantity occurred in streams with low canopy cover.Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
Griffith School of Environment
Science, Environment, Engineering and Technology
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Takahashi, Daisuke. "Theoretical investigation of the eco-evolutionary dynamics of food webs". 京都大学 (Kyoto University), 2014. http://hdl.handle.net/2433/189654.
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Vivas, Muñoz Jenny Carolina. "Trematodes modulate aquatic food webs by altering host feeding behaviour". Doctoral thesis, Humboldt-Universität zu Berlin, 2019. http://dx.doi.org/10.18452/20592.
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Parasiten können den Energietransfer in Lebensgemeinschaften über trophische Kaskaden beeinflussen, indem sie Änderungen in den Konsumenten-Ressourcen-Interaktionen induzieren. In der vorliegenden Arbeit wurde die Rolle von Trematoden auf das Freßverhalten ihrer Wirte auf zwei trophischen Ebenen untersucht. Vier verschiedene Süßwasserschnecken-Trematoden-Systeme wurden verwendet, um zu testen, ob ein allgemeines Muster für die Auswirkung von Infektionen auf die Grazingaktivität von Schnecken auf das Periphyton nachgewiesen werden kann. Die Grazingraten auf Periphyton bei infizierten Schnecken entweder höher, niedriger oder ähnlich denen derjenigen von nicht infizierten Artgenossen.
Augenparasiten können die Leistungsfähigkeit ihres Wirtes beeinträchtigen, was die Auswirkungen auf das Erkennen von Beutetieren, Raubtieren und Artgenossen hat. Mit Tylodelphys clavata experimentell infizierte Flussbarsche wurden mit zwei verschiedenen Beutetierarten eingesetzt, um das Fraßverhalten in Konkurrenz mit nicht infizierten Artgenossen zu untersuchen. Die Entfernung, aus der infizierte Fische die beiden Beutetierarten attackierten, war im Vergleich zu nicht infizierten Artgenossen signifikant kürzer. Die Tendenz war, dass nicht infizierte Fische mehr von den verfügbaren Beutetieren verzehrten. Um zu prüfen, ob der Fisch als Kompensation seine Beutepräferenz verändert, wurde die Beutezusammensetzung von Flussbarschen aus dem Müggelsees mittels Mageninhalts- und Stabilisotopenanalysen untersucht. Beide Methoden ergaben, dass sich die Fische mit zunehmender Intensität der Infektion selektiver ernährten, während sich geringer infizierte Fische Generalisten herausstellten. Die Ergebnisse dieser Studie bestätigen, dass Trematoden eine wichtige Rolle in Nahrungsnetzen spielen können, indem sie das Freßverhalten ihres Wirtes verändern. Darüber hinaus können Trematoden so die Stärke der Interaktion ihrer Wirte mit anderen Arten auf verschiedenen trophischen Ebenen beeinflussen.Parasites can influence energy transfer through communities via trophic cascades by inducing alterations on consumer-resource interactions. This study evaluated the role of trematodes on their host’s feeding behaviour at two trophic levels. Four different freshwater snail–trematode systems were used to test whether a general pattern can be detected for the impact of infections on snail periphyton grazing activity. Mass-specific periphyton grazing rates of infected snails were higher, lower, or similar to rates of non-infected conspecifics. The variation across systems may result from differences on how the parasites use the resources of the snail and thus affect its energy budget. Eye parasites can impair their host’s sensory performance with important consequences for the detection of prey, predators and conspecifics. European perch experimentally infected with Tylodelphys clavata were used to evaluate their feeding behaviour under competition with non-infected conspecifics, for two different prey species (Asellus aquaticus and Daphnia magna). The distance at which infected fish attacked both prey species was significantly shorter in comparison to non-infected conspecifics. Additionally, infected fish had more unsuccessful attacks and there was a general tendency that non-infected fish consumed more of the available prey. To evaluate whether fish alter their prey preference as a compensatory mechanism, perch from Lake Müggelsee were sampled and their diet was evaluated using both stomach content and stable isotope analyses. Both methods indicated that with increasing infection intensity fish had a more selective diet, while less intensively infected fish appeared to be generalist feeders. The results from this study confirm that trematodes can play a relevant role within food webs by altering their hosts’ feeding behaviour. Furthermore, in this way trematodes can affect the interaction strengths of their hosts with other species at various trophic levels.
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Moriarty, David Joseph Wulstan. "Productivity and trophic role of bacteria in acquatic food webs". Thesis, 1990, 1990. http://hdl.handle.net/2440/38537.
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Moriarty, David Joseph Wulstan. "Productivity and trophic role of bacteria in acquatic food webs". 1990, 1990. http://hdl.handle.net/2440/38537.
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Felix, Leonardo Gama. "Nutrient Dynamics and Foods Webs". Laboratório Nacional de Computação Científica, 2010. http://www.lncc.br/tdmc/tde_busca/arquivo.php?codArquivo=202.
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A food web comprises exchanges of matter and energy that occur among species and between biotic and abiotic environment. Given that abiotic components form the basal resources, the approach of this work consists of evaluating the effects of nutrients input in strategic models that describe food web and chain dynamics. Its focus lies on the determination of the nature of equilibrium populations as well as on their dynamics for different functional responses. Strategic models that describe the behavior of interactive populations under nutrient inputs are an important basis for outlining general phenomena that occur in community dynamics.Uma rede trófica reúne as trocas de matéria e energia que ocorrem entre as espécies e entre o meio biótico e abiótico. Visto que os componentes abióticos formam a fonte de recursos basais, a abordagem deste trabalho consiste na avaliação dos efeitos da entrada de nutrientes alóctones em modelos estratégicos que descrevem a dinâmica de redes e cadeias tróficas, concentrando-se na determinação das características das populações de equilíbrio e das dinâmicas das espécies com diferentes respostas funcionais. Modelos estratégicos que contêm informações acerca do comportamento de populações interativas frente à entrada de nutrientes são uma base importante no delineamento de fenômenos gerais que podem ocorrer dentro da dinâmica de comunidades.
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nnah, Marie Hannah Marie. "The effects of assembly method on food webs : integrating population dynamics, evolution and web size". Thesis, University of York, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.516620.
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Ptacnik, Robert. "Omnivory in planktonic food webs a study on the impact of mixotrophic flagellates and microzooplankton on food web dynamics and productivity". Kiel Inst. für Meereskunde, 2003. http://e-diss.uni-kiel.de/diss_825/d825.pdf.
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Fink, Patrick. "Food quality and food choice in freshwater gastropods field and laboratory investigations on a key component of littoral food webs". Berlin Logos-Verl, 2005. http://deposit.ddb.de/cgi-bin/dokserv?id=2788034&prov=M&dok_var=1&dok_ext=htm.
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Fink, Patrick. "Food quality and food choice in freshwater gastropods : field and laboratory investigations on a key component of littoral food webs /". Berlin : Logos-Verl, 2006. http://deposit.ddb.de/cgi-bin/dokserv?id=2788034&prov=M&dok_var=1&dok_ext=htm.
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Drexel, Jan Peter. "Contribution of Nitrogen Fixation to Planktonic Food Webs North of Australia". Thesis, Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/19733.
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Nitrogen fixation is no longer considered to be a minor factor of the nitrogen cycle in oceanic ecosystems. Recent geochemical and biological efforts have led to a significant increase in the estimated input of nitrogen to marine ecosystems by biological fixation, while molecular studies have increased our knowledge of the number and diversity of nitrogen fixers known to be active in the ocean. Although Trichodesmium spp. have long been viewed as the primary marine nitrogen fixers, recent efforts have shown that various members of the picoplankton community are also actively involved in nitrogen fixation. The relative abundance of different nitrogen fixers is an important ecosystem parameter since nitrogen fixers may differ significantly in their physiology, life history and ecology. Here we combine rate measurements and stable isotope natural abundance measurements to constrain the impact of N2 fixation in the waters north of Australia. Samples were collected in the Coral, Arafura, and East Timor Seas, thus spanning three distinct hydrographic regions. Our data show that Trichodesmium has a significant influence on the stable nitrogen isotope ratios of particulate and zooplankton biomass and suggest that Trichodesmium is a significant source of nitrogen for the pelagic ecosystem. Based on stable carbon isotope ratios, it is also likely that the pathways are indirect and nitrogen fixed by Trichodesmium enters the higher trophic levels via decomposition as dissolved organic and inorganic nitrogen. Picocyanobacteria showed high diazotrophic activity at some stations, but unlike Trichodesmium, their N2 fixation rate was not reflected in the stable N isotope ratios of particulate and zooplankton biomass. Our results suggest an important N contribution to biomass by diazotrophs in the Coral Sea, Arafura Sea and East Timor Sea.
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Duffy, Sean. "Persistence in intraguild predation food webs: possible solutions to a paradox". Thesis, McGill University, 2013. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=114273.
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Predator-prey interactions occurring between competitors that share a resource is a food web configuration known as intraguild predation (IGP). Theory dictates that IGP in its most basic configuration is often unstable, with strict criteria for coexistence of intraguild predator and intraguild prey. However, IGP is quite frequent in nature. The main objective of my thesis was to show how modifications to IGP interactions can promote the persistence of this food web configuration. First, I theoretically analysed how prey switching by the intraguild predator affected coexistence. I then focused on IGP in a mussel aquaculture system and empirically tested for factors modifying IGP pressures exerted by mussels on zooplankton intraguild prey. My IGP model with prey switching yielded coexistence over a greater range of parameters compared to the basic IGP model. In the mussel aquaculture system, age/stage structures and ontogenetic niche shifts were identified as factors that alter IGP interactions and potentially prevent the zooplankton intraguild prey from being excluded. This research adds to the literature on IGP interactions and provides insight on mechanisms that allow these food webs to persist.Les interactions prédateurs-proies se produisant entre les concurrents qui partagent une ressource représentent une configuration réseau alimentaire connu sous le nom de prédation « intraguilde » (IGP). La théorie dicte que l'IGP dans sa configuration la plus basique est instable, avec des critères stricts en matière de coexistence. Cependant les prédations intraguildes sont assez fréquentes dans la nature. Le principal objectif de ma thèse était de montrer comment les modifications des interactions IGP peuvent favoriser la persistance de ce réseau trophique. D'abord, j'ai analysé, de façon théorique, les effets de la commutation des proies par les prédateurs intraguildes sur la coexistence. Je me suis ensuite concentré sur les prédations intraguildes dans un système de mytiliculture. J'ai évalué, de façon empirique, les facteurs pouvant modifier les pressions provenant de la prédation intraguilde et étant exercées par les moules sur le zooplancton (proie intraguilde). Mon modèle IGP qui inclut la commutation des proies a abouti à la coexistence sur une plus grande gamme de paramètres par rapport au modèle de base IGP. Dans mon système de mytiliculture, la structure « âge / stade » ainsi que les déplacements de niches ontogénétiques ont été identifiés comme des facteurs modifiant les interactions IGP et qui empêchent potentiellement le zooplancton (la proie intraguilde) d'être exclu. Cette recherche s'ajoute à la littérature sur les interactions IGP et donne un aperçu sur les mécanismes qui permettent à ces réseaux trophiques de persister.
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Layer, Katrin. "Responses of freshwater food webs to spatial and temporal PH gradients". Thesis, Queen Mary, University of London, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.516661.
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Peralta, Guadalupe. "Food webs from natural to production forests: composition, phylogeny and functioning". Thesis, University of Canterbury. School of Biological Sciences, 2013. http://hdl.handle.net/10092/8556.
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Habitat loss and fragmentation have been identified as the main drivers of biodiversity loss. These drivers increase the proportion of habitat edges and change the configuration of landscapes. Habitat edges are known to affect ecological patterns and processes, however, is still unknown how these boundaries affect the assemblage of interactions among species within a community, and particularly its structure. Food webs depict not only the composition of the community, but also the feeding links, which represent a measure of energy flow. Therefore, they can inform about the relationships among community diversity, stability, and ecosystem functions.
This thesis explores the effects of habitat edges across native vs. managed forests on the food web of a tri-trophic system comprising plants, herbivores (Lepidoptera larvae) and predators (parasitoids). Particularly, it addresses three main objectives: 1) how food webs at habitat edges are assembled from the species and interactions present in the adjoining habitats; 2) how phylogenetic diversity and the coevolutionary signal among interacting species change across a habitat edge gradient; and 3) whether the mechanisms driving community-wide consumption rates and the ecosystem service of pest control are related to structural characteristics of the food webs.
The key findings of this thesis are that, despite the composition of species and interactions of native and managed habitats merging at their interface, food-web structure did not arise as a simple combination of its adjacent habitat webs, potentially due to differential responses of organisms to habitat edges. Moreover, beyond taxonomic composition, the phylogenetic diversity and signal of coevolution among interacting species also change between habitat types, even though this did not translate to changes in consumption rates. Consumption rates and their stability increased with complementarity and redundancy in resource-use among predators.
This reflects how environmental changes such as habitat fragmentation can have an effect beyond composition per se, affecting the assemblage of species interactions and even potentially interfering with natural evolutionary processes. Therefore, using interaction-network approaches for determining the impacts of changes may shed light on the underlying mechanisms driving such changes, and help to develop landscape management plans that reduce negative effects on species assemblages.
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Hogsden, Kristy Lynn. "Structure and function of food webs in acid mine drainage streams". Thesis, University of Canterbury. School of Biological Sciences, 2013. http://hdl.handle.net/10092/10357.
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Acid mine drainage (AMD) is a significant environmental issue worldwide, which often causes severe contamination and marked species losses in receiving streams. However, little is known about how this stress alters food webs and ecosystem function. I conducted a literature review, which revealed that AMD-impacted streams generally had depauperate benthic communities dominated by a few tolerant species and impaired ecosystem processes. Next, using survey and experimental-based approaches, I investigated food web structure and energy flow in these highly stressed streams, which typically have low pH (< 3), high concentrations of dissolved metals (Al, Fe), and substrata coated with metal hydroxide precipitates, on the South Island, New Zealand. Inputs of AMD caused substantial loss of consumers and reduced the overall number of links between species generating small and simplified food webs, with few invertebrates and no fish. Comparative analysis of food webs from a survey of 20 streams with either anthropogenic or natural sources of acidity and metals, indicated that anthropogenic sources had a stronger negative effect on food web properties (size, food chain length, number of links); an effect driven primarily by differences in consumer diversity and diet. However, the presence of fewer trophic levels and reduced trophic diversity (detected using isotopic metrics), were common structural attributes in AMD-impacted webs along a pH gradient, regardless of impact level. Furthermore, complementary dietary analyses of consumer gut contents and stable isotope signatures (δ13C and 15N) confirmed that primary consumers fed generally on basal resources and that there were few predatory interactions, which reflected low densities of small-bodied chironomids. This suggests that food quantity was unlikely to limit primary consumers but that reduced prey availability may be an additional stressor for predators. In these radically re-structured food webs, trophic bottlenecks were generated at the primary consumer level and energy flow to higher consumers was disrupted. However, streams still retained some limited function, including slow leaf litter breakdown, which provided detrital resources and supported the small food webs. Overall, my findings have furthered our understanding of these highly stressed stream ecosystems by providing new insights into interactions among species and trophic levels that structure food webs and enable function.
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Laws, Jacob. "Conduits of contamination to contemporary food webs of the Norfolk Broads". Thesis, Queen Mary, University of London, 2011. http://qmro.qmul.ac.uk/xmlui/handle/123456789/2424.
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During the 1960s-1980s antifouling applications containing the organotin tributyltin (TBT) were applied to craft on the Norfolk Broads, leaving a legacy of contaminants in sediments. Previously, no research had been undertaken to investigate the implications that this legacy may have for the ecological integrity of the Norfolk Broads aquatic ecosystem. Eight sites in the Norfolk Broads that represented a gradient of contamination (as measured by sediment TBT concentrations) were selected. Contamination was evident in invertebrates and fish but was lower than sediments, as total organic carbon and species specific metabolic capacity for TBT controlled bioavailability To examine TBT impacts at the community scale, novel metrics were applied to food webs defined by stable isotopes of carbon and nitrogen. Two metrics were reduced in response to increasing TBT contamination, suggesting simplification of food webs along the contaminant gradient; where loss of key food web properties such as trophic diversity and shortened food chain length could reduce resilience to further system perturbations. I hypothesised that chironomids emerging from sites contaminated with organotins would carry with them an organotin burden, which would be reflected in terrestrial predators such as spiders via trophic transfer. A combination of spider and chironomid stable isotopes (principally δ 13C) and isotope mixing models indicated considerable chironomid contribution to spider biomass at all four sites (34-88%). Subsequent organotin analyses revealed consistent low level, butyltin (di-butyltin; DBT) contamination in chironomids and spider predators from the most contaminated site.
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Pontius, Ruth Atkins. "The impact of zebra mussels (Dreissena polymorpha) on pelagic food webs". The Ohio State University, 2000. http://rave.ohiolink.edu/etdc/view?acc_num=osu1400072667.
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Garvey, James E. "Strong interactions and community structure: Testing predictions for reservoir food webs /". The Ohio State University, 1997. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487944660931703.
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Barrett, Nicholas John Barrett. "Effects Of Warming and Increased Sediment Inputs on Pelagic Food Webs". Miami University / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=miami1501154557516404.
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Zurbrügg, Corinne. "Degradation patterns of transgenetic Bt maize in soil and food webs /". Bern : [s.n.], 2008. http://www.ub.unibe.ch/content/bibliotheken_sammlungen/sondersammlungen/dissen_bestellformular/index_ger.html.
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Merkley, Steven S. "An Invasive Species Reduces Aquatic Insect Flux to Terrestrial Food Webs". BYU ScholarsArchive, 2011. https://scholarsarchive.byu.edu/etd/2806.
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Although it is well documented how introduced species can negatively affect native species, we only poorly understand how they may alter ecosystem functions. We investigated how an invasive fish affected the flux of aquatic insects to terrestrial food webs using mesocosms in a desert spring ecosystem. We compared aquatic insect emergence between alternative community states with monocultures and polycultures of two native species of fish, least chub (Iotichthys phlegethontis) and Utah chub (Gila atraria) plus, introduced western mosquitofish (Gambusia affinis). We tested three hypotheses: (1) aquatic insect biomass will be greater than terrestrial insect biomass and thus, constitute a vital source of energy for terrestrial consumers (2) invasive mosquitofish will negatively impact the biomass of emerging aquatic insects, and (3) terrestrial consumers will negatively respond to decreased emerging aquatic insect biomass. Aquatic insects represented 79% of the flying insect community, and treatments with mosquitofish significantly reduced emergent aquatic insect biomass by 60% relative to the control without mosquitofish. Behavioral traits of invasive species are important, because mosquitofish most heavily affected insects that emerged during the day. Also, spiders that build horizontal webs were negatively correlated with decreasing aquatic insect biomass. Invasive mosquitofish can achieve very dense populations because of their high intrinsic rate of population increase, which can significantly disrupt the flow of energy between aquatic and terrestrial ecosystems, thereby reducing the energy available for terrestrial consumers.
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Figueroa, David. "Food web dynamics : new patterns from southern South America and North Wales UK, and the role of basal species structuring food webs". Thesis, Queen Mary, University of London, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.582554.
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Food webs, defined as "who eats whom" in nature, have become a central topic within community ecology and thus they have been used to understand general ecological patterns such as biodiversity and species interactions as well as material and nutrient flows within ecosystems. In South America the knowledge of the taxonomy and distribution of freshwater invertebrates is incomplete and fragmented. Previous studies have focused on specific taxonomic groups and some countries such as Brazil and Argentina. In contrast, there have been many aquatic food webs published for UK freshwater systems with high levels of taxonomic resolution. This thesis aims to examine food web patterns in two geographically separated systems. The effects of systematic taxonomic aggregation on food web properties were examined and the relationship between consumer and prey body size revisited. A total of 24 food webs were examined in Chilean and Welsh streams, where 6128 invertebrate guts were examined to establish feeding interactions. These Chilean and Welsh food webs are amongst the largest, most complete and fully resolved. In both systems there was a high proportion of basal species, combined with low proportions of top and intermediate species. Significant differences were detected in most food web properties, in comparison to previous studies, where basal species were aggregated to coarser categories. No significant relationship between the body size of the consumers and their prey was found in either Chilean or Welsh streams. These results differ substantially from published data, and we attribute these differences to the greater taxonomic resolution particularly on the basal resources.
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Pi, Lasternas Sébastien Marie Arthur. "Implications of phytoplankton cell death losses forcarbon flux in Oceanic food-webs". Doctoral thesis, Universitat de les Illes Balears, 2012. http://hdl.handle.net/10803/108002.
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En el océano, las condiciones ambientales adversas independientes de la predación tienen como resultado la muerte y lisis celular del fitoplancton que resulta en la liberación de carbono orgánico disuelto (PDOC) a la columna de agua. Las comunidades bacterianas heterotróficas marinas, normalmente dependientes de esta fuente de carbono para su metabolismo, obtienen un beneficio de la liberación de carbono recién sintetizado a la vez que participan en su reciclaje a través de la red trófica microbiana. A pesar de la repercusión que este proceso puede tener en el ciclo del carbono en los océanos, actualmente se desconoce cual es su contribución en ambientes marinos naturales y en el actual escenario de cambio global. El principal objetivo de esta tesis fue analizar las relaciones existentes entre la mortalidad de células del fitoplancton, la proporción de carbono orgánico disuelto (DOC) liberado por el fitoplancton y la supervivencia microbiana bajo diversas condiciones ambientales. La salud de comunidades naturales fitoplanctónicas y bacterianas, la producción primaria total y la liberación fitoplanctónica de DOC fueron determinadas in situ en diferentes regiones oceánicas que comprendieron los mares Mediterráneo, Ártico, Antártico y Atlántico. Los resultados obtenidos en este estudio demostraron la existencia de una relación entre condiciones ambientales tales como la temperatura del agua y la disponibilidad de nutrientes en la muerte celular del fitoplancton. Además, la mortalidad celular del fitoplancton determinada en estos ambientes puede explicar un 41.4% de la PDOC relativa a la producción primaria total, y en regiones oceánicas oligotróficas del noroeste del Océano Atlántico, este proceso sustentó una alta viabilidad bacteriana. Los resultados obtenidos durantes esta tesis resaltan el crucial papel de la lisis celular del fitoplancton en los océanos y ayudan a comprender cuales son las principales vías de transferencia de carbono desde la fotosíntesis hasta el metabolismo heterotrófico bacteriano.Important phytoplankton losses by cell death, independent of grazing are occurring in the ocean. Phytoplankton cells have been described to die upon encountering adverse environmental conditions, and cell death and lysis would result in the release of the carbon incorporated in the photosynthesis by the phytoplankton as dissolved organic carbon (PDOC). The availability of dissolved organic carbon (DOC) is a major constraint for the heterotrophic bacteria, consequently the release by cell mortality of the recently photosynthate carbon is expected to benefit the bacterial community and should be channelled through the microbial food web. All this processes have been poorly documented and the contribution of the phytoplankton cell death to the release of PDOC has not been yet explored in natural communities. The goal of this PhD Thesis is to provide quantitative information on phytoplankton and bacteria cell death in natural communities and to document the fraction of DOC released by phytoplankton (PDOC) under contrasting natural conditions. The exploration of the relationships between the phytoplankton cell mortality, DOC released by phytoplankton (PDOC) and microbial survival would contribute to better understand the path of carbon from photosynthesis to heterotrophic bacteria by cell death processes. Contrasting environmental conditions and communities from different oceanic regions including the Mediterranean Sea, Arctic, Antarctic and Atlantic oceans were studied. Evaluations of the in situ health status of the natural phytoplanktonic communities and bacteria were analyzed by testing the cell membrane permeability; a property that define cell death in cell biology. The total primary production, and the DOC production by phytoplankton were quantified to explore its dynamic with regard to the variability in phytoplankton cell mortality. The bacterial cell survival was also assessed under the same contrasting conditions mediating by the quantification of percentage of living heterotrophic bacteria. The proportion of dead of phytoplankton cells from the diverse phytoplankton populations encountered in the different communities, were related to environmental conditions as water temperature and nutrients availability, and helped to identify their competitive success. Consistent proportions of dead natural phytoplanktonic cells were found during this study that could represent in average about half of the total (40.5 %) phytoplankton abundance. Phytoplankton mortality constitutes a major process implicated in the production of dissolved organic carbon, as the percentage of phytoplankton dead cells explained the 41.4 % of the percentage of released production (PDOC) relative to total primary production. The large production of PDOC observed here, represented in average the half of the total primary production (54.4%) and supported, at the oligotrophic NE Atlantic Ocean, a higher bacterial viability.