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Population ecology of the dog-faced water snake (Cerberus rynchops) at Sungei Buloh Wetland Reserve, Singapore
Author
Chim, Chee Kong
Supervisor
Diong, Cheong Hoong
Abstract
Ecological traits of a population of the dog-faced water snake, Cerberus rynchops, from the man-made brackish ponds of Sungei Buloh Wetland Reserve (SBWR), Singapore, were determined or estimated using mark-recapture data collected during low tides. Population size was estimated at 1114 individuals (approximately 81 snakes/ha). Sex ratio was 1:1. The population was dominated by snakes of 350 - 500 mm snout-vent length (SVL) throughout the year. A large proportion of females reached body size of sexual maturity but neonates were rarely encountered. Males were larger than females in general, but females attained a larger body size. Males had relatively longer tails, and females had relatively wider heads. Females grew twice as fast as males. Snakes were highly associated with water bodies, such as the edges of tidal streams and tidal pools, but they were also encountered infrequently on emerged mudflats. Cerberus rynchops appears to be largely sedentary and capable of homing behavior.
Snake diets consisted of fifteen types of fish from nine families, freshly moulted shrimps and snapping shrimps. The population had a narrow niche breadth, the diet was dominated by only two types of prey, which are the Javanese ricefish (Oryzias javanicus) and the mollies (Poecilia spp.) Snakes were observed using two hunting methods - 'sit-and-wait' and 'open-mouth searching'. About 15% of the snakes contained food. Snakes consumed an average of four prey items per meal. Although snakes consumed as many as 46 prey items per meal, 44% of the snakes consumed a single item. There was a weak prey size-predator size relationship. Prey items averaged 5.95 mm (maximum body diameter) and 0.34 g (wet mass). Snakes were capable of consuming prey that were more than four times as wide as their head and more than a fifth of their body mass. Total prey mass per meal averaged 1.53 g. Although large snakes were capable of consuming larger prey items and had larger meals than small snakes, they continued to feed on small prey. Diets were influenced by sex and the reproductive status of snakes.
Reproduction occurred throughout the year. All gravid snakes continued to feed during captivity. Gestation length was estimated to be four to seven months. Females are capable of producing multiple clutches in a year. The interval between two clutches produced by some individuals was less than one month. Total clutch size averaged 4.4 offspring although up to twelve offspring were produced. Primary sex ratio was 1:1. Larger females produced more and larger offspring. Neonates of both sexes did not differ in SVL, body mass or head width, but males had relatively longer tails than females. Offspring had mean SVL of 154 mm and mean body mass of 2.34 g. The smallest female to reproduce had 336 mm SVL. The ratio of this length to the mean offspring SVL is about 2.2:1. No apparent trade-off exists between clutch size and offspring size. Total clutch mass (TCM) averaged 10.02 g. Mean of relative clutch mass (RCM) ranged from 0.17 to 0.37. Maternal body size was related to TCM, but not to RCM.
Snake diets consisted of fifteen types of fish from nine families, freshly moulted shrimps and snapping shrimps. The population had a narrow niche breadth, the diet was dominated by only two types of prey, which are the Javanese ricefish (Oryzias javanicus) and the mollies (Poecilia spp.) Snakes were observed using two hunting methods - 'sit-and-wait' and 'open-mouth searching'. About 15% of the snakes contained food. Snakes consumed an average of four prey items per meal. Although snakes consumed as many as 46 prey items per meal, 44% of the snakes consumed a single item. There was a weak prey size-predator size relationship. Prey items averaged 5.95 mm (maximum body diameter) and 0.34 g (wet mass). Snakes were capable of consuming prey that were more than four times as wide as their head and more than a fifth of their body mass. Total prey mass per meal averaged 1.53 g. Although large snakes were capable of consuming larger prey items and had larger meals than small snakes, they continued to feed on small prey. Diets were influenced by sex and the reproductive status of snakes.
Reproduction occurred throughout the year. All gravid snakes continued to feed during captivity. Gestation length was estimated to be four to seven months. Females are capable of producing multiple clutches in a year. The interval between two clutches produced by some individuals was less than one month. Total clutch size averaged 4.4 offspring although up to twelve offspring were produced. Primary sex ratio was 1:1. Larger females produced more and larger offspring. Neonates of both sexes did not differ in SVL, body mass or head width, but males had relatively longer tails than females. Offspring had mean SVL of 154 mm and mean body mass of 2.34 g. The smallest female to reproduce had 336 mm SVL. The ratio of this length to the mean offspring SVL is about 2.2:1. No apparent trade-off exists between clutch size and offspring size. Total clutch mass (TCM) averaged 10.02 g. Mean of relative clutch mass (RCM) ranged from 0.17 to 0.37. Maternal body size was related to TCM, but not to RCM.
Date Issued
2009
Call Number
QL666.O6 Chi
Date Submitted
2009