Reproductive and Trophic Ecology of an Assemblage of Aquatic and Semi-Aquatic Snakes in Tonle Sap, Cambodia
We studied the reproductive and trophic ecology of a group of aquatic and semi-aquatic snakes that face severe hunting pressure in Cambodia. Over a two-year period we sampled hunters' catches, measuring and dissecting a total of 8982 specimens of seven snake species, five of which belong to the family Homalopsidae. The seven species—Enhydris enhydris, Enhydris longicauda, Homalopsis buccata, Enhydris bocourti, Erpeton tentaculatus, Xenochrophis piscator, and Cylindrophis ruffus—all inhabit Tonle Sap Lake, the largest lake in South-East Asia. All species are sexually dimorphic in either body size or tail length. The larger species, E. bocourti and H. buccata, have a larger size at maturity, and the non-homalopsids, X. piscator and C. ruffus, have the highest and lowest fecundities, respectively. Clutch size increases significantly with female body size in all species, and with body condition in E. enhydris. Our data also suggest that relative investment in reproduction increases with size in E. enhydris, which has the largest sample size. All species except one are synchronized in their timing of reproduction with the seasonally receding flood waters of the lake. There was variation in both the frequency of feeding and the prey size and type among species, with the homalopsids more similar to one another than to the other non-homalopsid species. The prey to predator mass ratio ranged from 0.04 to 0.1 in the homalopsids, compared to 0.15 to 0.17 in the non-homalopsids. There was also variation in the feeding frequency between the sexes that differed between species and six species continued to feed while gravid. These detailed life history analyses can help provide a basis for assessing conservation options for these heavily exploited species.Abstract
Fecundity–body length relationships for seven snake species. Clutch size is measured as the number of eggs per breeding bout and is combined for vitellogenic and embryonic eggs. Each data point represents a gravid female. Linear regression equations and R2 values can be found in Table 3.
Fecundity ranges for seven snake species, based on the linear regressions of clutch size (number of eggs) versus SVL shown in Fig. 1. Minimum values are based on the estimated clutch size at length at maturity (Table 2) and maximum values are based on the estimated clutch sizes at maximum observed female length. The mean observed clutch sizes are also shown.
Breeding seasons for the seven snake species. The bars represent the percentage of all females that were reproductive, including vitellogenic (white bars) and embryonic (solid bars). The line represents the mean testis volume ± standard error. Data shown are from June 2004 until March 2006 and no data exist for April and May 2005. The sparse amount of data for 2004, for all species except E. enhydris, is the result of lower sampling effort that year. The graph in the bottom left-hand corner illustrates the seasonal fluctuation of water level in the lake (data extracted from MRC/FIN Water Utilisation program, 2000).
Prey mass relative to predator mass (± standard error). Symbols a, b, and c denote homogeneous subsets to which the species belong, derived from post hoc analyses following a one-way ANOVA of mean prey/predator mass ratio. Those with different symbols are therefore statistically significantly different from one another.
Proportion of individuals containing food in the stomachs. This is shown for males, females, non-breeding and breeding females for all species separately. Values above bars denote sample sizes. Where the number of females in the sample is greater than the sum of the breeding and non-breeding females, this is due to missing data on the reproductive status of females due to putrefication of specimens.
Contributor Notes
Associate Editor: G. Haenel.