Synthesis and reactivity of enediynes

The discovery of a class natural products with anti-cancer properties, the enediynes, has stimulated interest in their research. Due to their cytotoxicity, these compounds are not feasible for use in cancer treatment, however, synthetic work has centered around improved stability, reduced toxicity and elucidation of the mechanism of the Bergman cyclization reaction. Protocols utilizing palladium-catalysed cross coupling reactions have been used extensively in the synthesis of enediyne analogues. Little work to date has investigated the effect of heteroatoms on the success of coupling reactions, thermal Bergman cyclizations and photochemically induced cyclizations. In this thesis, a synthetic study involving the coupling reactions o f nitrogenous aromatic halides, halotriflates and a series of alkynes will be presented. Several enediyne analogues were synthesized in moderate to high yields, isolated and characterized. In general, it was observed that nitrogen heteroatoms increase the reactivity toward Sonogashira coupling reactions. In order to examine the effect o f resonance and inductive effects on the reactivity under Sonogashira conditions, a series o f competitive reactions between m- or p-substituted aryl iodides and iodobenzene were performed. In general, electron withdrawing substituents in the m- or p-positions increased the reactivity, while electron donating substituents decreased it. It was observed that resonance effects have a larger effect on reactivity than inductive effects. Thermal and photochemical cyclization studies were performed for the nitrogenous aromatic enediynes synthesized. None o f the enediynes were observed to cyclize thermally, while only the TMS- and phenyl-substituted enediynes were observed to photochemically cyclize

Habitat selection in Eumeces fasciatus, the Five-lined skink, at Point Pelee National Park, Ontario, Canada.

The habitat patch in which an animal resides can have profound fitness consequences. I studied habitat selection in a population of Five-lined skinks at Point Pelee National Park, Ontario, Canada. Skinks did not use the entire resource spectrum that was available. Preference was shown for larger, moderately decayed debris which provided a moist and relatively constant microclimate. Habitat selection was density-independent, suggesting that intraspecific competition does not structure the pattern of habitat use. A high level of parental care occurred, with females brooding and guarding clutches. Females varied their body contact with eggs and moved eggs vertically to control moisture. Human disturbance, centred at boardwalks, has a negative effect on skink abundance and distribution through reduction of debris. The incorporation of an Allee effect in habitat selection models is extended, and a new graphical model the Ideal social distribution is presented which may better explain patterns observed in Five-lined skinks or other social species. (Abstract shortened by UMI.)Dept. of Biological Sciences. Paper copy at Leddy Library: Theses & Major Papers - Basement, West Bldg. / Call Number: Thesis1992 .H435. Source: Masters Abstracts International, Volume: 31-03, page: 1138. Chairman: Robert T. M\u27Closkey. Thesis (M.Sc.)--University of Windsor (Canada), 1991

Species richness, species turnover, and spatial dynamics of amphibian communities.

Ecological investigations have traditionally focused on local scales and have been of short duration. The importance of scale to perception of patterns in nature is now recognized, and there is increased interest in determining the relative roles of local versus regional, and contemporary versus historical processes in structuring populations and communities. Over three years I surveyed 180 southwestern Ontario ponds to record amphibian presence and measure habitat and landscape variables. My goal was to document and explain patterns of amphibian species richness and incidence, and to investigate how these patterns change spatially and temporally. Species richness and incidence differed significantly among regions and were associated with a combination of both local and regional variables. However, the amount of regional woodlands accounted for most of the variance. Water chemistry played only a minor role in affecting species richness and distribution; however, laboratory studies revealed toxic effects of nitrates at realistic field concentrations. Species richness was significantly lower at predatory fish ponds compared to other ponds. Amphibians having large bodies or clutch sizes, or anti-predator defenses, co-occurred with fish more frequently than small species. Introduced fish produced large-scale patterns through their effect on local assemblages. Local extinction of bullfrogs was correlated with increased relative abundance of its intraguild prey, the green frog. The entire fauna showed nested subset structure. Species that require woodlands and those vulnerable to fish predation showed the highest degree of nestedness. Incidence was positively correlated with species-specific dispersal capabilities. The system is characterized by high species turnover which has resulted in trends of both increased and decreased species incidence. Green frog occupancy, abundance, and turnover was both scale and location dependent, extinctions occurred only at the local scale, and small populations were vulnerable. I developed habitat quality models for use in conservation. Incidence and duration of site occupancy were positively related to habitat quality. In this system fish predation, a contemporary local process, and historical regional deforestation appear to be the dominant processes affecting amphibian communities. Large-scale perspectives are necessary to explain the patterns in amphibian communities and to assess the status of species.Dept. of Biological Sciences. Paper copy at Leddy Library: Theses & Major Papers - Basement, West Bldg. / Call Number: Thesis1996 .H42. Source: Dissertation Abstracts International, Volume: 59-08, Section: B, page: 3846. Adviser: Robert T. M\u27Closkey. Thesis (Ph.D.)--University of Windsor (Canada), 1997

Restored Agricultural Wetlands in central Iowa: Habitat Quality and Amphibian Response

Amphibians are declining throughout the United States and worldwide due, partly, to habitat loss. Conservation practices on the landscape restore wetlands to denitrify tile drainage effluent and restore ecosystem services. Understanding how water quality, hydroperiod, predation, and disease affect amphibians in restored wetlands is central to maintaining healthy amphibian populations in the region. We examined the quality of amphibian habitat in restored wetlands relative to reference wetlands by comparing species richness, developmental stress, and adult leopard frog (Lithobates pipiens) survival probabilities to a suite of environmental metrics. Although measured habitat variables differed between restored and reference wetlands, differences appeared to have sub-lethal rather than lethal effects on resident amphibian populations. There were few differences in amphibian species richness and no difference in estimated survival probabilities between wetland types. Restored wetlands had more nitrate and alkaline pH, longer hydroperiods, and were deeper, whereas reference wetlands had more amphibian chytrid fungus zoospores in water samples and resident amphibians exhibited increased developmental stress. Restored and reference wetlands are both important components of the landscape in central Iowa and maintaining a complex of fish-free wetlands with a variety of hydroperiods will likely contribute to the persistence of amphibians in this landscape

Anuran responses to spatial patterns of agricultural landscapes in Argentina

Context: Amphibians are declining worldwide and land use change to agriculture is recognized as a leading cause. Argentina is undergoing an agriculturalization process with rapid changes in landscape structure. Objectives: We evaluated anuran response to landscape composition and configuration in two landscapes of east-central Argentina with different degrees of agriculturalization. We identified sensitive species and evaluated landscape influence on communities and individual species at two spatial scales. Methods: We compared anuran richness, frequency of occurrence, and activity between landscapes using call surveys data from 120 sampling points from 2007 to 2009. We evaluated anuran responses to landscape structure variables estimated within 250 and 500-m radius buffers using canonical correspondence analysis and multimodel inference from a set of candidate models. Results: Anuran richness was lower in the landscape with greater level of agriculturalization with reduced amount of forest cover and stream length. This pattern was driven by the lower occurrence and calling activity of seven out of the sixteen recorded species. Four species responded positively to the amount of forest cover and stream habitat. Three species responded positively to forest cohesion and negatively to rural housing. Two responded negatively to crop area and diversity of cover classes. Conclusions: Anurans within agricultural landscapes of east-central Argentina are responding to landscape structure. Responses varied depending on species and study scale. Life-history traits contribute to responses differences. Our study offers a better understanding of landscape effects on anurans and can be used for land management in other areas experiencing a similar agriculturalization process.Facultad de Ciencias ExactasCentro de Investigaciones del Medioambient

Exotic fish in exotic plantations: a multi-scale approach to understand amphibian occurrence in the mediterranean region

Globally, amphibian populations are threatened by a diverse range of factors including habitat destruction and alteration. Forestry practices have been linked with low diversity and abundance of amphibians. The effect of exotic Eucalyptus spp. plantations on amphibian communities has been studied in a number of biodiversity hotspots, but little is known of its impact in the Mediterranean region. Here, we identify the environmental factors influencing the presence of six species of amphibians (the Caudata Pleurodeles waltl, Salamandra salamandra, Lissotriton boscai, Triturus marmoratus and the anurans Pelobates cultripes and Hyla arborea/meridionalis) occupying 88 ponds. The study was conducted in a Mediterranean landscape dominated by eucalypt plantations alternated with traditional use (agricultural, montados and native forest) at three different scales: local (pond), intermediate (400 metres radius buffer) and broad (1000 metres radius buffer). Using the Akaike Information Criterion for small samples (AICc), we selected the top-ranked models for estimating the probability of occurrence of each species at each spatial scale separately and across all three spatial scales, using a combination of covariates from the different magnitudes. Models with a combination of covariates at the different spatial scales had a stronger support than those at individual scales. The presence of predatory fish in a pond had a strong effect on Caudata presence. Permanent ponds were selected by Hyla arborea/meridionalis over temporary ponds. Species occurrence was not increased by a higher density of streams, but the density of ponds impacted negatively on Lissotriton boscai. The proximity of ponds occupied by their conspecifics had a positive effect on the occurrence of Lissotriton boscai and Pleurodeles waltl. Eucalypt plantations had a negative effect on the occurrence of the newt Lissotriton boscai and anurans Hyla arborea/meridionalis, but had a positive effect on the presence of Salamandra salamandra, while no effect on any of the other species was detected. In conclusion, eucalypts had limited effects on the amphibian community at the intermediate and broad scales, but predatory fish had a major impact when considering all the scales combined. The over-riding importance of introduced fish as a negative impact suggests that forest managers should prevent new fish introductions and eradicate fish from already-occupied ponds whenever possible