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The structure and dynamics of a freshwater benthic food webWarren, P. H. January 1988 (has links)
No description available.
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Cell cycle dynamics and their application to calculating in situ growth rates in two heterotrophic protozoa : a flow cytometric approachWhiteley, Andrew Steven January 1994 (has links)
No description available.
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The effect of environmental noise on population and community dynamicsPetchey, Owen Leonard January 1997 (has links)
No description available.
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Seasonal microbial dynamics in two ultra-oligotrophic Antarctic freshwater lakesHenshaw, Tracey January 2001 (has links)
No description available.
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Demographic and trophic dynamics of fishes in relation to hydrologic variation in channel and floodplain habitats of the Brazos River, Texas.Zeug, Steven Christopher 02 June 2009 (has links)
Large rivers in North America have been subjected to a variety of hydrologic
alterations that have negatively impacted aquatic fauna. These impacts have triggered
restoration efforts, including management of flows, to restore or maintain ecological
integrity. Ecological data relevant to flow management and habitat restoration is scarce,
and conceptual models of ecosystem function have been widely applied to large rivers
despite a lack of quantitative evaluation of these models. Here, I examine demographic
and trophic dynamics of fishes with divergent life histories and trophic guilds in relation
to habitat heterogeneity and flow variability in a relatively unaltered floodplain system:
the Brazos River, Texas. Reproductive activity of fishes with three divergent life history
strategies was positively associated with long-term river hydrology, although species
with alternate strategies exploited different portions of the hydrograph (peak flow versus
increasing flow). Despite the positive association with hydrology, low-flow periods
were favorable for recruitment, and food resources for larvae and juveniles were denser
during these periods. Some species used both oxbow and channel habitats during some
point in their life cycle, whereas other species appeared to be almost entirely restricted to
one habitat type. Terrestrial C3 macrophytes accounted for a significant fraction of the biomass of
most consumer species examined. Small-bodied species in oxbow lakes assimilated
large fractions of biomass from benthic algae, whereas this pattern was not observed in
the river channel. Frequent flow variations in the river channel may reduce algal
standing stocks, and significant contributions from autochthonous algal sources may
only occur during low-flow periods. Trophic positions of detritivores indicated that
terrestrial carbon sources were assimilated, for the most part, via invertebrates rather
than by direct consumption. My results indicate that current conceptual models are too
vague to provide accurate predictions for restoration strategies in rivers with variable
flow regimes. Flow and habitat management strategies that focus on reproducing key
features of historical fluvial dynamics are likely to be more successful than strategies
that focus on single indicator species or flow dynamics that differ from the historical
hydrograph.
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Selenium dynamics in Canadian Rocky Mountain lakesFortin, Barbra Linda Unknown Date
No description available.
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Mechanisms and mitigation of food web change in stream ecosystemsGraham, Sharon Elizabeth January 2013 (has links)
Freshwater ecosystems reflect the condition of their surrounding landscape, and thus are particularly vulnerable to anthropogenic stressors associated with human land-use. One of the most prevalent stressors on stream ecosystems in agricultural regions, such as the Canterbury Plains of New Zealand, is eutrophication, or increased primary productivity. The aim of this thesis was to investigate effects of eutrophication on stream communities, specifically food web structure and ecosystem function. From a food web perspective, eutrophication is a shift in the form and amount of available energy from externally-produced (allochthonous) to internal (autochthonous) basal resources. Such shifts are frequently associated with land-use intensification, due to riparian vegetation removal and increased nutrient inputs, both of which enhance autochthonous production. A field survey across a gradient of eutrophication showed that eutrophic stream food webs are largely autochthonously-based and often contain large numbers of defended primary consumers, which form trophic bottlenecks and prevent energy from reaching higher trophic levels. Consequently, while there is more total energy available, less of that energy is in a usable form for stream food webs. Moreover, I found that eutrophic streams are largely composed of generalist consumers, which shift their diets to refocus on autochthonous resources with increasing productivity. Given that eutrophication causes food web resources to become more homogenous and was a primary driver of food web change, I tested whether reintroducing allochthonous subsidies would alter or reverse the negative effects of eutrophication. To do this I conducted a short-term community assembly experiment and a year-long population biomass accrual study. I found that the simplified, generalist-dominated communities in eutrophic streams did not respond to changes in resource diversity as predicted by food web theories, which are based on more diverse food webs. After restoration of allochthonous subsidies, defended generalist taxa continued to dominate the invertebrate communities. However, while restoring allochthonous subsidies did not mitigate the numerical dominance of defended consumers, the biomass accrual of other, previously excluded desirable taxa, such as mayflies and predatory invertebrates, increased following resource additions. This indicates that more energy reached the top of the food web, suggesting that resource additions alleviated trophic bottlenecks. Overall, my findings have advanced current knowledge about key mechanisms driving food web responses to both anthropogenic stress and to restoration efforts, which can be applied to improve management and restoration of stream ecosystems.
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Selenium dynamics in Canadian Rocky Mountain lakesFortin, Barbra Linda 06 1900 (has links)
I investigated, water, invertebrates and fishes from lakes in Banff National Park and Kananaskis Country, Alberta for selenium (Se), an element known to be toxic to vertebrates. At some depths, Se concentrations in sediment exceeded recognized thresholds for bird and fish reproductive impairment. Se concentrations in water were over USEPA guidelines after spring melt runoff. In aquatic invertebrates, Se concentrations exceeded values known to cause reproductive impairment in fish and bird predators. Se concentrations in all fish species exceeded known thresholds for reproductive impairment in avian consumers and the majority surpassed concentrations that would negatively affect wildlife and human consumers. Se concentrations in some fish species have significantly increased over the past 6-16 years. The strongest predictors of fish Se concentrations were growth rate, condition factor, age, weight, trophic position (within lakes) and vegetation type (among lakes). These results suggest that consumption advisories are desirable for several lakes in the Banff and Kananaskis area, and that Se concentrations in fish from other area lakes should be investigated. / Ecology
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Allometric structure and topology of food webs: Energetic constraints conserve food-web structure across ecosystems and spaceDigel, Christoph 24 April 2014 (has links)
No description available.
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Long-term changes to food web structures and mercury biomagnification in three large, inland North American lakesPoulopoulos, John 31 January 2013 (has links)
Numerous anthropogenic disturbances have occurred in large lakes over recent decades. These may alter concentrations of the biomagnifying contaminant mercury (Hg) in fish, but long-term impacts of disturbances on Hg trophodynamics are poorly understood. Elemental analyses of archived museum ichthyology specimens could be used to study historical, pre-disturbance fish food webs, but there is uncertainty about effects of chemical preservatives on the results of such analyses. In this thesis, long-term preservation effects were studied, and archived fish were used to reconstruct historical food webs and Hg trophodynamic patterns in three large North American lakes, Nipigon, Simcoe and Champlain. After 24 months of formalin/ethanol preservation, fish muscle delta-15N and delta-13C had average changes of +0.4 ‰ and -0.9 ‰, respectively. Shifts in mean Hg concentration was +5 % after 12 months. A suite of 26 other elements analyzed over 24 months showed consistent responses to preservation, usually involving an increase in concentration immediately following preservation. In the second phase of the thesis, stable isotope and Hg analyses were performed on archived and modern fish from the study lakes, dating to the 1920s-60s and 2006-7, respectively. Trophic relationships were often relatively stable over time, but stable isotope metrics revealed a decrease in Lake Nipigon delta-15N range and less pelagic feeding among Lake Simcoe pumpkinseed and yellow perch. In Lake Champlain, the re-introduction of lake trout in recent decades did not have a major effect on overall food web dimensions. Significant Hg biomagnification factors were found in 1920s and 2006-7 Lake Nipigon (which were not statistically distinguishable from each other) and 2006 Lake Champlain. These biomagnification factors ranged from 0.09 to 0.17, which is within the range found in other studies globally. Archived fish and government monitoring records indicated that fish Hg concentrations decreased in Lakes Simcoe and Champlain since historical periods, but remained similar or increased in Lake Nipigon. This thesis confirms the utility of archived fish for elemental analyses. It highlights the risks of Hg contamination and food web change that may be faced by remote lakes, and it provides evidence for relatively stable Hg biomagnification rates in large lakes. / Thesis (Ph.D, Biology) -- Queen's University, 2013-01-30 15:43:33.438
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