Population size, population structure and habitat utilization of Bufo asper Gravenhorst, 1829 in Tarn Lord Noi Cave, Kanchanaburi Province

Abstract

A total of 15 surveys were carried out monthly from July 2001 to June 2002 to investigate population size, population structure, and habitat utilization of Asian giant toad, Bufo asper, inhabiting Tarn Lord Noi Cave, Kanchanaburi Province. The toads that were found in any survey were captured and individually marked using toe-clipping method. Sex, age, weight, snout to vent length, breeding behavior, and location were recorded for all toads. After the toads had been examined, they were released at the point of capture. Using the Jolly-Seber model of population estimation, the estimated population size varied from 71.9 ± 7.9 to 91.9 ± 8.5 individuals. The male was dominant in number relative to the female and the young almost throughout the sampling period. However, the population size of the male was smaller than the population size of the female during the breeding time in May 2002 in which the sex ratio was 1 : 1.27. For the other sampling time, the sex ratio varied from 1 : 0.22 to 1 : 0.75. The size that was frequently found for the male, the female, and the young were between 90 to 110 mm, 110 to 140 mm, and 30 to 90 mm, respectively. Population sizes of the male and the female correlated with the temperature but the correlation was on the opposite way. The change of female population size coincided with the temperature but conversely related for the male. A large number of the toads showed movement between inside and outside of the cave for both breeding and non-breeding time. Most of the toads exhibited highly area fidelity behavior for both breeding and non-breeding time (Chi-square: P<0.05). There was no significant difference in habitat utilization between sexes and between the male of different sizes for both breeding and non-breeding time. Reproduction and survival seemed to play the important role for the population change and habitat utilization of them. The obtained data during March 2001 to July 2002 suggested that the toad inhabiting Tarn Lord Noi Cave was not explosive breeder. They took about 5 months in rainy season for each breeding time. The breeding times were quite similar for 2 successive years that were during April to August 2001 and March to July 2002. The result from the study of population, habitat utilization and breeding time revealed that Tarn Lord Noi Cave was important as a breeding site for this population.