Thesis (M.Sc.)--Chulalongkorn University, 2008

Life history patterns of homalopsid snakes were investigated between inside (Ban Badan, Wang Nam Kheaw District) and outside the Khorat basin (Ban Borthong, Kabin Buri District), Thailand from April 2006 to May 2007. Five species of homalopsid snakes were found at each study site. The similarity index of the snake assemblages from both study sites was 86%. Enhydris subtaeniata were found only inside the Khorat basin whereas E. bocourti were found only outside the Khorat basin. Species diversity inside the Khorat basin was higher than outside the Khorat basin but the abundance was less. Enhydris enhydris was the dominant species at 45.14% and 81.36% at inside and outside the Khorat basin, respectively and the sex ratio of this species was not different between study sites. Sexual size dimorphism was found in both study sites and most morphological characters of females were significantly larger than males, except for tail length. Both sexes of snakes from outside the Khorat basin were significantly larger than snakes from inside the Khorat basin. Small fish were usually found in homalopsid guts but larger fish were occasionally found. Fish in Family Cyprinidae and Family Belontiidae were dominant prey types inside and outside the Khorat basin, respectively. Prey types did not completely overlap between study sites (niche overlap = 0.66) and snakes from outside the Khorat basin tend to feed on various prey types. The size at first reproduction of females E. enhydris was 31.4 cm in SVL at both study sites. Many size characters of female E. enhydris and E. subtaeniata correlated with clutch size and clutch mass. The number of gravid females observed in each month were significantly correlated with total precipitation at both study sites. Significant differences in the reproductive condition of females between study sites were found in morphological characteristics and reproductive cycle. Seasonal and continuous reproduction tend to occur for homalopsid snakes inside and outside the Khorat basin, respectively. Environmental factors including total precipitation and food availability might bring about differences in abundance, morphological characteristics and reproduction of homalopsid snakes inside and outside the Khorat basin. Furthermore, morphological characters, diet and reproduction of a poorly known homalopsid snake, E. subtaeniata, and some other semi-aquatic snakes were documented