Thesis (Ph. D.)--University of Wyoming, 2005. / Title from PDF title page (viewed on Feb. 22, 2008). Includes bibliographical references (p. 75-87).

Wetlands occurring on natural river floodplains typically have more dynamic hydrology, because of influences from the river, than man-made wetlands or those associated with reclaimed minelands. For wetland-associated species, fluctuating water levels can affect patch availability, connectivity and potentially habitat quality, and therefore drive metapopulation dynamics. Differences in hydrology between wetland complexes could change food webs and consequently the trophic diversity of the communities occupying these areas. My first objective was to assess the spatial and temporal variation in occupancy and turnover rates of a semi-aquatic small mammal at 2 hydrologically distinct wetland complexes over 3 years in southern Illinois. My second objective was to determine spatio-temporal variation in the trophic structure of small mammals at 2 wetland complexes (floodplain and mineland) in southern Illinois. To address my first objective, I live-trapped marsh rice rats (Oryzomys palustris) during 2011-2013 at 9 wetland patches on the Mississippi River floodplain and 14 patches at a reclaimed mineland. I used multi-season occupancy modeling to estimate initial occupancy, detection, colonization and extinction rates. Catch per unit effort differed markedly between the 2 sites (27 captures/1,000 trap-nights at the floodplain site vs. 8 at the mining site). Estimates of detection probability increased with an increase in effort (number of traps per night per wetland patch). Occupancy probability was similar between sites and positively related to patch size. Patch colonization probability at both sites was related negatively to total rainfall 3 weeks prior to trapping. In addition, the variation in colonization probability among years, was different between sites, with colonization in 2013 being much lower at the mining site than at the floodplain. An increase in total rainfall 3 months prior to trapping led to a substantial increase in extinction probability on the floodplain, but not at the mining site. Differences in metapopulation dynamics and relative abundance between the 2 sites can be attributed to differences in hydrology and habitat quality. Although rice rats were present at the mining site in much lower numbers than at the floodplain site, these less-natural wetland complexes might serve as valuable refuges for species occurring in increasingly fragmented landscapes. For my second objective, I collected hair samples from 6 species of small mammals (n = 416) occurring at these wetland complexes. I analyzed C and N stable isotopes for 3 mammal taxa (Oryzomys palustris, Peromyscus spp,, Microtus ochragaster) to compare diet between species, sites, and, times. Food sources (vegetation and invertebrates) were collected at each site to form the isotopic baseline. Using stable isotope mixing models, I found no seasonal difference in diet composition, but signatures varied between sites. Oryzomys palustris at both wetland complexes incorporated primarily (70-80%) invertebrates in their diet, and used more C4 vegetation (30%) than C3 (0%). Isotope signatures of Peromyscus diets at the floodplain site were similar to that of Oryzomys, with ~80% invertebrates and >C4 vegetation than C3 vegetation (~20% and 0%, respectively). At the mining site, Peromyscus were at a much lower trophic level and consumed 70% vegetation with C3 plants making up a greater part of their diet than C4 vegetation (50% and 20%, respectively). Microtus was at a lower trophic position than the other 2 species at both sites. These isotope results point to reduced niche overlap between Oryzomys and Peromyscus at the mining site, perhaps due to lower habitat quality and limited suitable resources. Although small mammals had narrower diet breadths at the mining site, none of the species was at a higher trophic position at the mining site than at the floodplain site. At the floodplain site, the more dynamic hydrology might have given rise to higher biodiversity and consequently provided more resources to allow small mammals to use similar food items.

No description available.

Much of the world's species diversity is located in tropical and sub-tropical ecosystems, and a better understanding of the ecology of these systems is necessary to stem biodiversity loss and assess community- and ecosystem-level responses to anthropogenic impacts. In this dissertation, I endeavored to broaden our understanding of complex ecosystems through research conducted on the Cinaruco River, a floodplain river in Venezuela, with specific emphasis on how a human-induced perturbation, commercial netting activity, may affect food web structure and function. I employed two approaches in this work: (1) comparative analyses based on descriptive food web characteristics, and (2) experimental manipulations within important food web modules. Methodologies included monthly sampling of fish assemblages using a variety of techniques, large-scale field experiments, extensive stomach content and stable isotope analyses. Two themes unite the information presented: (1) substantial spatial and temporal variability in food web structure, and (2) how body-size can be used to generalize species-interactions across this complexity. Spatial variability occurred at various scales, from among small fish assemblages on seemingly homogeneous sand banks, to differences among landscape scale units (e.g. between lagoons and main river channel). Seasonal variability was apparent in predation patterns, with relative prey availability and body size primarily resulting in decreasing prey sizes with falling water levels. Body size was also related to functional outcomes of species interactions, for example, a size-based response of prey fishes to large-bodied piscivore exclusion. This pattern was further substantiated at the landscape-scale, as differences in assemblage structure among netted and un-netted lagoons were largely size-based. Trophic position of fish and body size was not found to be related, likely due to the diversity of prey available to consumers, and may signify that commercial netting activity will not decrease food chain lengths. In sum, by describing human impacts within a food web context, I endeavor to provide predictive power regarding a specific human-induced environmental problem, yet still allowing for generality that will broaden the theoretical foundations and applications of food web ecology.

The purpose of the study was to investigate possible environmental impacts of a reduced catchment area (~25 %) for Kaunisjärvi lake and Patojoki river due to establishment of a iron ore mine in Kaunisvaara, Pajala municipality. To accomplish this, two methods were used; first a literary study was inducted to establish impacts of reduced inflow to lakes and reduced flow in rivers. Secondly, the state of the waters was determined by collecting background data from the mining company (Northland Resources SA) which included chemical- and biological parameters. The result showed that a reduced inflow can affect a lake by either eutrophication or oligotrophication, depending on the lakes condition and the character of the inflow, which in turn has impacts on the entire food-web. Reduced flow in rivers also has impacts on the entire food-web by increased water temperature, decreased dissolved oxygen levels, decreased inundation (witch effects nutrient and organic material exchange), decreased biodiversity in phytoplankton, benthos and fish and inhibiting migration, studies differed in effects on pH and alkalinity. The result also showed that both Kaunisjärvi and Patojoki are affected by nutrient load and organic matter, which impacts the entire ecosystem of the waters. Possible consequences for Kaunisjärvi and Patojoki of reduced inflow and reduced flow are discussed. The report concluded that the reduced catchment area will have impacts on environmental goals set by EU and also on national level, but that the interest of exploitation weighs higher.

Stable isotope analysis is a tool employed in ecological studies to provide information on the movement of elements and energy through a system. The stable carbon and nitrogen isotope analysis of aquatic organisms has been commonly used to address questions related to energy transfer between organisms and to identify the reliance of aquatic organisms on different sources of organic matter within the system. Within the rivers, stable isotope analysis has been used to describe food webs and connect conditions within the watershed with the river. The Grand River watershed is a predominantly agricultural watershed which receives inputs from ~26 MWWTP and is managed for flow by multiple large reservoirs and weirs. The stable isotope values of aquatic organisms within this watershed were analyzed from samples collected between May and September, 2007. Sites were selected in relation to three different municipal waste water treatment plants (MWWTP) in the centre of the watershed and along a 200 km stretch of the main stem of the Grand River. Results show that stable isotope analysis can be used to differentiate organisms collected from different sites and which represent different trophic levels within the river system under select conditions. Sites which are influences by inputs from organic matter or nutrients within distinct isotope values can be distinguished easily if the input is large and the isotope values are significantly distinct from background values. For smaller inputs changes in stable isotope values were not observed relative the background variability in the system. In this case, sites should be selected to allow for the characterization the variation in isotope values already occurring within the river. Samples collected later in the growing seasons have more distinctive isotope values are between sites. At sites where seasonal variation is greater, the organisms collected may not show a clear separation between trophic levels. A lack of knowledge regarding the time period represented by the tissues of the organisms challenges interpretation these results. It is concluded that stable isotope values of aquatic organisms reflected the condition of this watershed. For nitrogen increasing loads from point sources were accompanied by increasing isotope values. Stable isotope values decreased over the river reach where recovery in river condition occurs as a result of ground water inputs. The influence of individual large MWWTP and reservoirs was observable and the management of the MWWTP and reservoir appears to affect the changes in isotope values which are observed.

Stable isotope analysis is a tool employed in ecological studies to provide information on the movement of elements and energy through a system. The stable carbon and nitrogen isotope analysis of aquatic organisms has been commonly used to address questions related to energy transfer between organisms and to identify the reliance of aquatic organisms on different sources of organic matter within the system. Within the rivers, stable isotope analysis has been used to describe food webs and connect conditions within the watershed with the river. The Grand River watershed is a predominantly agricultural watershed which receives inputs from ~26 MWWTP and is managed for flow by multiple large reservoirs and weirs. The stable isotope values of aquatic organisms within this watershed were analyzed from samples collected between May and September, 2007. Sites were selected in relation to three different municipal waste water treatment plants (MWWTP) in the centre of the watershed and along a 200 km stretch of the main stem of the Grand River. Results show that stable isotope analysis can be used to differentiate organisms collected from different sites and which represent different trophic levels within the river system under select conditions. Sites which are influences by inputs from organic matter or nutrients within distinct isotope values can be distinguished easily if the input is large and the isotope values are significantly distinct from background values. For smaller inputs changes in stable isotope values were not observed relative the background variability in the system. In this case, sites should be selected to allow for the characterization the variation in isotope values already occurring within the river. Samples collected later in the growing seasons have more distinctive isotope values are between sites. At sites where seasonal variation is greater, the organisms collected may not show a clear separation between trophic levels. A lack of knowledge regarding the time period represented by the tissues of the organisms challenges interpretation these results. It is concluded that stable isotope values of aquatic organisms reflected the condition of this watershed. For nitrogen increasing loads from point sources were accompanied by increasing isotope values. Stable isotope values decreased over the river reach where recovery in river condition occurs as a result of ground water inputs. The influence of individual large MWWTP and reservoirs was observable and the management of the MWWTP and reservoir appears to affect the changes in isotope values which are observed.

Much of the world's species diversity is located in tropical and sub-tropical ecosystems, and a better understanding of the ecology of these systems is necessary to stem biodiversity loss and assess community- and ecosystem-level responses to anthropogenic impacts. In this dissertation, I endeavored to broaden our understanding of complex ecosystems through research conducted on the Cinaruco River, a floodplain river in Venezuela, with specific emphasis on how a human-induced perturbation, commercial netting activity, may affect food web structure and function. I employed two approaches in this work: (1) comparative analyses based on descriptive food web characteristics, and (2) experimental manipulations within important food web modules. Methodologies included monthly sampling of fish assemblages using a variety of techniques, large-scale field experiments, extensive stomach content and stable isotope analyses. Two themes unite the information presented: (1) substantial spatial and temporal variability in food web structure, and (2) how body-size can be used to generalize species-interactions across this complexity. Spatial variability occurred at various scales, from among small fish assemblages on seemingly homogeneous sand banks, to differences among landscape scale units (e.g. between lagoons and main river channel). Seasonal variability was apparent in predation patterns, with relative prey availability and body size primarily resulting in decreasing prey sizes with falling water levels. Body size was also related to functional outcomes of species interactions, for example, a size-based response of prey fishes to large-bodied piscivore exclusion. This pattern was further substantiated at the landscape-scale, as differences in assemblage structure among netted and un-netted lagoons were largely size-based. Trophic position of fish and body size was not found to be related, likely due to the diversity of prey available to consumers, and may signify that commercial netting activity will not decrease food chain lengths. In sum, by describing human impacts within a food web context, I endeavor to provide predictive power regarding a specific human-induced environmental problem, yet still allowing for generality that will broaden the theoretical foundations and applications of food web ecology.

Food webs are good ecological macro-descriptors and their study is important in ecology in understanding nutrient cycles, tracing and quantifying energy and in describing trophic interactions within an ecosystem. The knowledge of food web finds applications in various natural sciences disciplines but also in many productive sectors. This study investigated the structure of the food web of a shallow lake in the Pantanal flood plain. The food web included two macrophytes, six aquatic insects, four crustaceans and 24 fish species. Sources of carbon for the various organisms living in the lake were identified through the values of δ13C exhibited by the organisms. The δ15N signature was used to estimate the trophic position of each organism. A cluster analysis based on the two isotopic signatures revealed six different feeding guilds and emphasized on the broad occurrence of omnivory among animals living in the lake. This study revealed that the use of food carbon was the most important factor that structured the lake community. Very low values of δ13C in zooplankton, benthic dwellers and bottom-feeder organisms as well as similarities between the gradient of δ13C and that of use of methane oxidizing bacteria informed on the possible use of biogenic methane as a source carbon and energy for the lake biota.

Global warming will affect every level of biological organization from the metabolism of individuals to the functioning of ecosystems. I explored the effects of warming on three rock-pool meioinvertebrate communities along a latitudinal gradient (temperate, tropical, and sub-Arctic regions) to determine effects on community and food-web structure and functioning. Warming affected regions differently, having a positive effect on sub-Arctic communities, a negative effect on temperate communities, and intermediate responses in tropical communities in terms of abundance, stability and extinction frequency. Differences in structural properties of the food webs supported the insurance hypothesis: that greater redundancy in webs results in greater stability, and helped to explain why the tropical community was more stable than the temperate community in warmed treatments. My study highlights the importance of considering differential response of species and communities from different latitudes and the importance of food web structure in predicting species response to global climate change.