제주지역에서 맹꽁이(Kaloula borealis)의 생태에 관한 연구

Abstract

The mean snout-vent length (SVL) of the Kaloula borealis is estimated at 45.2mm, its HL (head length) at 10.6mm, HW (head width) at 14.4mm, and SL (snout length) and ED (eye diameter) at 4.4mm. Its FLIMB (forelimb length) was estimated at 19.4mm and HLIMB (hindlimb length) at 44.9mm. The EN (distance between eye and nostril) was half the size of IND (internarial distance), and the IOD (interorbital distance) was longer than the IND but smaller than the SL or ED. The length of the forelimb was half the size of SVL and the length of the hindlimb was similar to that of SVL. The third finger of the forelimb was the longest and the first toe was the shortest. The fourth toe of the hindlimb was the longest and the first toe was the shortest. The tBL (body length) of a tadpole was smaller than half of its tTL (total length) and its tIDE (intereye distance) was longer than its tTH (tail height). The abdomen of the tadpole was initially transparent but turned to be gray and black-dotted at Gosner stage 28. K. borealis was found to stay at the same place in their habitat under rocks, in piles of stones, or in the soil for 5 to 7 days. This suggests that K. borealis dwells in the same place for a long time and migrates for the night within a limited area. The spawning sites of K. borealis in a large number of wetlands were surveyed in Jeju Island between May and August from 2007 to 2010. The subjects' habitation was investigated by their calls throughout a rainy night up to the next morning. Spawning sites ascertained the existence of their eggs and tadpoles. In the results, 83 wetlands were found to be used as spawning sites. Of these, most of the spawning sites were permanent wetlands. In addition, 81.9% of the wetlands in Jeju Island were at an altitude of 150m or lower. K. borealis spawned in shallow water not more than 50cm in depth. By region, 54 wetlands were in Jeju-si and 29 wetlands were in Seoguipo-si. This might be attributed to the relatively high farming activity in Seogwipo-si compared to Jeju-si. In Seongsan-eup where a reedy marsh stretches out, wide spawning sites were well-preserved compared to other regions. In order to analyze the environmental factors influencing the breeding activities of the K. borealis, spawning sites in Daejung-Eub, Jeju Island were investigated for 4 years from 2008 to 2011. Rainfall, humidity, temperature, barometric pressure, and wind speed were analyzed together. Spawning activities according to precipitation revealed that the major factors influencing breeding activities included rainfall, humidity, and barometric pressure. The most important factor was rainfall, suggesting that K. borealis spawns when it rains hard. Temperature was also important for breeding activity. The breeding season was from May to August, meeting the conditions for breeding activities. Like the previous studies on other anurans in temperate regions, rainfall and temperature might be important for the breeding activities of K. borealis on Jeju Island. The feeding habits of K. borealis was studied among 52 out of 56 specimens collected in Daejung-up, Jeju Island in June 2011. The stomach contents were analyzed by stomach flushing method. In the result, the main preys for K. borealis were found to be Diptera sp., Harpalidae, Formicidae, and Drosophilidae. K. borealis fed on all sizes of small preys while individuals with large SVL fed on big preys. By feeding on a large amount of food with less activities, the individuals with large SVL increased their energy efficiency. In many cases, K. borealis fed on Diptera sp. or Drosophilidae that were slow but capable of flying. This suggests that K. borealis has a sit-and-wait form of preying rather than an active searching technique for acquiring food. The age of K. borealis was determined by skeletochronology performed among 38 males and 58 females sampled in the Daejung-eup during their breeding season in June 2009. SVL and body weight (BW) were also analyzed. The mean value of SVL was 43.69±3.44 ㎜ in males and 46.32±4.23㎜ in females. The age at first reproduction was estimated to be 2 years in males and 3 years in females. The oldest males and females were 8 and 10 years of age, respectively, indicating that the longevity of K. borealis might be more than 8 years for males and 10 years for females and that females significantly live longer than males. In growth curve for K. borealis using von Bertalanffy growth model, the growth coefficient (K) was 0.56 in male and 0.41 in female; the asymptotic size was 46.41 ㎜ in male and 50.22 ㎜ in female. There were three major reasons for the decline in the K. borealis in Jeju Island. The first was the loss of habitats due to expansion of housing areas and road constructions. Second, the expansion of farmland caused a decrease in spawning habitats in swamps. Of note, pesticide container waste and fertilizer wrappers were frequently found in the swamps. This may have destroyed habitats by chemical toxicity. Third, predators like carps and mudfishes discharged in the swamp decreased the number of tadpoles by predation. In fact, an adult K. borealis actually avoided spawning in swamps where predators were found. To preserve K. borealis on Jeju Island, identification of spawning sites should be considered first. To preserve the spawning swamp in their habitats, reclamation of wetland to farmland should be prohibited together with management of farming waste, including pesticide bottles and fertilizer wrappers. Because non-native predator species discharged in the wetland may feed on K. borealis tadpoles, the introduction of non-native species should be carefully observed in spawning sites of K. borealis on Jeju Island.