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Thesis (M.Sc. (Tropical Medicine))--Mahidol University, 1982.

Thesis (M.Sc. (Microbiology)) -- Mahidol University, 1979.

Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1986. / Vita. Abstract. Includes bibliographical references (leaves 153-164). Also available via the Internet.

Various ecological parameters, including soil pH, calcium, and habitat complexity have been suggested in the literature as having influence on land snail abundance and diversity. I compared relationships between 15 ecological parameters and snail abundance and diversity. 5,393 snails of 72 species were collected from 60 sites in 2007. Habitat observations were recorded in the field and soil core samples taken at each site and later analyzed for soil moisture, organic matter, cation exchange capacity, pH, calcium, magnesium, zinc, potassium, phosphorus, sulfur, boron, manganese, iron and copper. Statistical analyses were run using these soil factors plus a habitat complexity index (from combined values assigned to different levels of vegetation, topography and exposed rock), for a total of 15 parameters. To reduce the number of parameters and arrive at a more biologically meaningful model, Bayesian Information Criteria analysis (BIC) was run for abundance and diversity. The resulting best-fitted BIC model for abundance contained 3 parameters (pH, S, and habitat complexity) (R2 = 0.47), all of which were positively associated with abundance in a multiple regression analysis. For diversity, the best-fitted BIC model also contained 3 parameters (Ca, Fe, and habitat complexity) (R2 = 0.54). Ca and habitat complexity showed a positive association in the multiple regression analysis, but Fe was inversely associated with diversity, suggesting Fe could potentially act as an ecological limiting factor to it. These results suggest that land snail abundance and diversity are best treated separately in analyses, as they are influenced by different variables, with the exception of habitat complexity, which is suggested to have a positive association with both abundance and diversity. The regression model equations have potential value in that they can be used to predict snail abundance and diversity in areas that have not been assessed.

Typescript. Includes vita and abstract. Bibliography: Includes bibliographical references (leaves 61-68).

Pomacea bridgesii is a snail species native to tropical and sub-tropical regions, where it usually faces variability in water, temperature and oxygen level. This study of the effect of temperature on mass-specific oxygen consumption (ṀO2) and its relation to body weight shows that the ṀO2 of juvenile snails in normoxia (18-21 kPa) acclimated at temperature of 25°C ranged from 5 to 58 µMol O2/g/h, with a mean of 41.4 ± 18.3 µMol O2/g/h (n=7). Adult snails in normoxia at 25°C show less variation, ranging from 13 to 23 µMol O2/g/h , with a mean of 24.4± 6.1 µMol O2/g/h (n=12). The Q10 value for juvenile snails was higher in the interval 25-30°C (Q 10=5.74) than in the interval 20-25°C (Q10= 0.286). In adult snails, Q10 was higher in the interval 20-25°C (Q10=3.19). ṀO2 of P. bridgesii in relation to body weight showed a negative linear correlation between metabolic rate and body weight with b values between 0.23 and 0.76. Also, both juvenile and adult snails exhibited weak O2 regulation. In general, the different respiratory characteristics between juvenile and adult snails might be related to the differences of individual life history, which caused them to perform differently in face of temperatures change. Additionally, Pomacean snails species originated in tropical habitats where there is a lack of thermal fluctuation. For this reason, Pomacean snails may be less likely to have evolved effective thermal acclimation capabilities.

The influence of temperature on the bionomics of Bulinus (Physopsis) globosus, Biomphalaria pfeifferi and Lymnaea natalensis has been studied both in the laboratory under controlled conditions and in the field under normal seasonal influences. Field studies were carried out in two different localities, one a semi-permanent pond and the other a temporary waterbody. For this purpose a sampling implement was developed. The results show the seasonal progression of these populations both with respect to estimated numbers and the size distribution of the snails. The rate of actual increase at different seasons was calculated for the three species where the data were sufficient. In the laboratory the snails were maintained at various temperatures, other conditions being kept standard. Daily records of mortality and fecundity of various cohorts reared from the egg stage enabled the compilation of life tables fof the speciesand from these data were calcualted the intrinsic rate of natural increase and other parameters. Effects of crowding in aquaria were studied. From the data obtained in the laboratory it was possible to predict the distribution and population potential for each species for snail of various environmental conditions. These predictions were, in fact, confirmed by field observation.