No description available.

Diets of two zooplanktivores were studied in Lake Winnipeg: the non-indigenous rainbow smelt (Osmerus mordax) and the native cisco (Coregonus artedi). Gut contents of smelt (70-130 mm total length) and cisco (100-200 mm TL) were concurrently collected with zooplankton (integrated vertical tows) from pre-determined locations throughout Lake Winnipeg in 2010 and 2011. When spatially separated, both zooplanktivores showed similar shifts from preference for fast-moving copepods during low total zooplankton density to slow-moving large cladocerans (Daphnia spp. and Eubosmina sp.) during high total zooplankton density. When spatially overlapped in the North Basin, dietary overlap was high between smelt and cisco, but possible vertical segregation was apparent during daylight-dark trawls. Diel variation in smelt diet was minimal. Overall, impact of smelt on the food web seemed weaker than in other smelt-invaded lakes, potentially owing to the warm, shallow nature of Lake Winnipeg providing a poorer quality habitat than cooler, deeper lakes.

Diets of two zooplanktivores were studied in Lake Winnipeg: the non-indigenous rainbow smelt (Osmerus mordax) and the native cisco (Coregonus artedi). Gut contents of smelt (70-130 mm total length) and cisco (100-200 mm TL) were concurrently collected with zooplankton (integrated vertical tows) from pre-determined locations throughout Lake Winnipeg in 2010 and 2011. When spatially separated, both zooplanktivores showed similar shifts from preference for fast-moving copepods during low total zooplankton density to slow-moving large cladocerans (Daphnia spp. and Eubosmina sp.) during high total zooplankton density. When spatially overlapped in the North Basin, dietary overlap was high between smelt and cisco, but possible vertical segregation was apparent during daylight-dark trawls. Diel variation in smelt diet was minimal. Overall, impact of smelt on the food web seemed weaker than in other smelt-invaded lakes, potentially owing to the warm, shallow nature of Lake Winnipeg providing a poorer quality habitat than cooler, deeper lakes.

Introduced cichlid species are increasingly more common in tropical freshwater systems and expanding in range, often with negative consequences to receiving systems. To better understand, monitor, and manage these populations, improved cichlid sampling protocols are required. The goal of this study was to (1) evaluate diel electrofishing and gill netting sampling catch efficiency, and (2) compare two non-lethal methods for extracting stomach contents from Butterfly Peacock Bass Cichla ocellaris. This study suggests that electrofishing, particularly at night, may be a more appropriate gear for sampling cichlid species in the littoral zone of reservoirs, as gill nets were more time intensive, had more variable catch rates, and exhibited considerable selectivity. Pulsed gastric lavage was more effective than acrylic stomach tubes for extracting stomach contents from Butterfly Peacock Bass and was less injurious, with bruising of the stomach wall the most common injury being observed.

Organismal invasions have repeatedly been cited as both a driving force behind global change and beneficiaries of that change. Although many drivers of these invasions have been well studied, few studies have addressed invasions through the perspective of native symbiont communities. In the Mountain Lake region of Virginia, crayfish host diverse assemblages of obligate cleaning symbionts known as branchiobdellida. This cleaning symbiosis has been found to result in significant fitness benefits for native crayfish. Historical survey work showed that invasive crayfish, known to be intolerant of symbionts, were introduced into the region by the 1960s. I carried out an extensive regional survey to determine how this invasion has progressed and what impacts it is having on the native crayfish-branchiobdellida symbiosis. Survey results show that invasive crayfish have successfully spread throughout the region, resulting in the displacement of native crayfish. Additionally, findings suggest that invasion results in significantly reductions in abundance and richness in native symbiont communities. To determine mechanisms contributing to observed impacts on native symbionts, I carried out a study that simulated displacement of native crayfish by invasive crayfish in a controlled setting. This study found that as native crayfish are increasingly displaced by invasive crayfish, both symbiont dispersal and survival are negatively affected. This potential loss of symbiosis caused by invasion may reduce symbionts on native crayfish below abundances necessary for fitness benefits, exacerbating the negative impacts of invasions and presenting a major conservation issue in invaded systems. / M. S. / Introductions of non-native organisms are widely recognized for the negative impacts they have on native biodiversity. Although ongoing study has been directed at understanding many of the factors contributing to invasions, few studies address invasion through the perspective of native symbionts. In the Mountain Lake region of Virginia, crayfish host multiple species of small worms, known as crayfish worms, that provide cleaning services to their crayfish host. These services have been found to provide health benefits to native crayfish. Historical surveys found that invasive crayfish, known to be intolerant of crayfish worms, were introduced into the region by the 1960s. To determine how far invasive crayfish have spread and what impacts they are having on native organisms, I carried out a survey of the region. This survey found that invasive crayfish are now widespread in the region. Additionally, findings suggest that the introduction of invasive crayfish results in reductions in both the number of worms and worm species present. These reductions may be significant enough to prevent health benefits given to native crayfish from occurring. In addition to this survey, I carried out a study under controlled settings to determine what causes negative impacts on native crayfish worms. This study found that as invasive crayfish displace native crayfish, crayfish worms are increasingly killed due to the intolerance of invasive crayfish to the worms. These findings suggest symbiosis should be included in studies of invaded systems if we are to fully understand the introduction and spread of invasive species.

A major trend in invasion biology is the development of models to accurately predict and define invasive species and the stages of their invasions. These models focus on a given species with an assumed set of traits. By doing so, they fail to consider the potential for differential success among different source populations. This study looked at the inland invasion of Rhithropanopeus harrisii in the context of a current invasion model. This species has been introduced worldwide, but has only invaded freshwater reservoirs within the state of Texas (United States) indicating a potential difference amongst source populations. Previous studies indicate that this species should not be capable of invading inland reservoirs due to physiological constraints in the larvae. A more recent study gives evidence to the contrary. To investigate whether the inland populations are in fact successfully established, I attempted to answer the following questions: Can inland populations successfully reproduce in the inland reservoirs and rivers? If so, what factors in the native environment could have led to the evolution of this ability? What are the impacts of this species in the inland reservoirs and what is its potential spread? I combined a larval developmental study, conspecific and heterospecific crab competition trials, field collections, gut content analysis, shelter competition trials with crayfish, and larval and adult dispersal study to answer these questions. I showed that Rhithropanopeus harrisii is established in the inland reservoirs and capable of spreading. I demonstrated that in the native populations along the Gulf coast of the United States, this species is the least aggressive and is therefore likely excluded into lower salinity waters during reproductive periods. This likely led to a lowered salinity tolerance in the larval stages, which predispose these populations to successful introductions in inland freshwater bodies. I showed that the crabs are capable of outcompeting juvenile crayfish for shelter at high densities and therefore warrant management in order to reduce their effect. This study indicates a need for the invasion models to take the source population into account in order to ensure effective and prudent management strategies.

No description available.

The transportation of organisms in the ballast water of cargo ships has been recognized as a source of invasive species despite current control measures. Pathogenic bacteria in the ballast tank have been studied but the total diversity of the ballast tank bacterial community has not been examined. This study is the first to characterize the total bacterial community within a ballast tank by constructing a clone library from a ballast water sample from a cargo ship in the Port of Houston, amplified ribosomal rDNA restriction analysis (ARDRA) and phylogenetic analysis. Bacterial communities in Texas ports and bays were also examined using denaturing gradient gel electrophoresis (DGGE), looking at both temporal and spatial variations for effects of deballasting activity. This ballast tank bacterial community had a high level of diversity (95%) with the clone library only representing 40% of the total community of the tank. Most probable originating habitats of the ballast bacteria were: marine pelagic (40%), estuarine (37%), coastal (6%), freshwater (3%) and other (14%), even though this ballast tank was exchanged with pelagic water. Predominate groups were alpha- and gammaproteobacteria, a few betaproteobacteria and bacteriodetes, and one each of verrucomicrobia, planctomycetes and actinobacteria, but no pathogens were detected. The data reveals a ballast tank that consists of half marine-pelagic, half port bacteria, revealing a low efficacy of exchange control methods and potentially invasive bacteria. The bacterial communities of five ships that exchanged ballast water in the Pacific Ocean shared on average 50% similarity. Two ships that exchanged ballast water in temperate latitudes were more similar than three other ships that exchanged in tropical latitudes, showing a correlation between location of exchange and community similarity. The bacterial communities of the Ports of Houston and Galveston exhibit stable, seasonal successions over one year. The port and bay systems of Texas exhibited spatial variations in bacterial communities related to salinity levels. Both experiments did not show evidence of community disruption by deballasting activities. This study shows that ballast water is a viable vector for invasive bacterial transport, although impact on Texas estuarine systems seems minimal.

Woody plants are encroaching into a karst savanna on the Edwards Plateau in central Texas, but their impact on hydrology is unclear because of high variability in soil depth and uncertainties about shallow and deep root contributions to water uptake, and water dynamics in rocky soil. The overall objectives of this study are to quantify contributions of shallow and deep roots to water uptake, and to quantify the impact of rock on soil hydraulic properties and water storage. A study was conducted in a karst savanna with ~50% woody cover to monitor spatial and temporal variations in soil moisture and root water uptake with neutron probe and time-domain reflectometry measurements. Bulk density was measured using gamma densitometry. Measurements were made to a depth of 1.6 m in a 25 m  25 m grid (5 m node spacing). The results showed that rock created high spatial variability in water storage. Water storage capacity in the measurement grid ranged from 185 to 401 mm, and coupled with heterogeneous distribution of trees led to high spatial variability in root water uptake. Most of the water uptake came from the upper 1 m of the soil profile, but 10% came from below 1.6 m. This indicated that roots had access to water stored within the bedrock, possibly in soil pockets. Statistical analysis showed that spatial distribution of θ was significantly correlated with rock distribution in the profile. Laboratory evaporation measurements showed that Small volume fractions of rock can increase evaporation from soils by slowing upward movement of water, thereby maintaining capillary connectivity to the surface for a longer period of time. Two simulation models, van Genuchten (VG) and Durner, were compared with the data from evaporation experiments. Results showed that the Durner model was more appropriate than the VG model for describing water retention and hydraulic conductivity of rocky soils.

Background: Lespedeza cuneata is a perennial invasive legume native to Asia that is common across grasslands in the eastern half of the United States and parts of Canada. The competitive nature and limited palatability of L. cuneata for grazers in the tallgrass prairie has made it an undesirable and invasive weed. Objectives: This study was conducted to investigate an invasive species management plan for restored grasslands and prairie areas. Methods: Study plots (n=144) for experiment 1 (summer treatment) were established at Crab Orchard Wildlife Refuge in Jackson County Illinois in August of 2012 and were situated to contain infestations of the target species. Two herbicides, in five concentrations were applied in August of 2012. A native seed mix was added to a portion of the summer plots later, in February of 2013. These treatments were assessed in June and August of 2013 to determine herbicide effects on stem count and percent cover of L. cuneata, along with the composition and percent cover of other species present. Spring herbicide applications (n=18) for experiment 2 were established, assessed for L. cuneata cover and density, and treated with two herbicide treatments in May of 2013. Spring treatments were identical to existing plots and were re-assessed in August 2013 to determine species composition and the abundance of L. cuneata. Seed was not added to these plots. Analysis: Mixed Model analysis by site was performed to test the effect of herbicide and seeding treatments on L. cuneata for both experiments 1 &2. The summer plots were also tested for effects on other plant groups. A repeated measures PERMANOVA along with ANOSIM and PERMADISP was performed to assess community composition response to seeding and herbicide treatments in the summer plots. Results: Abundance of L. cuneata was reduced 67 to <90% following herbicide treatment in Experiments 1 and 2. There were no differences in the effectiveness of herbicide treatments in in experiment 1, sites 1 &3, and in experiment 2. Supplemental seeding in the summer plots did not reduce the abundance of L. cuneata consistently across sites. Conclusion: Considerable short-term control of the target species was achieved in both the summer and spring plots, providing a window of opportunity for the imposition of additional methods of control. However, data from the summer plots suggest recovery of L. cuneata some sites, indicating further control would be necessary, with potentially the addition of other control methods or site alterations.