Project Title
The Biology and Ecology of Rice Field Vertebrates.

The life history, population and feeding biology of two species of frog (Rana cancrivora and R. limnocharis) were studied for approximately five rice growing seasoning the rice growing district of Tanjung Karang, Selangor, Malaysia. The results showed that the breeding periods of the two frogs were correlated with the irrigation phase of the rice growing season and were not correlated with the rainfall. The frog were also found to have two breeding peaks annually as opposed to a single peak for the same species in other localities.

Comparison of the life history aspects of two species showed that R. cancrivora female produced more, and larger sized, eggs than R. limnocharis female. This then produced a chain effect whereby R. cancrivora larvae developed faster and metamorphosed at a larger size than those of R. limnocharis, and then continued to grow at a faster rate, attained a larger size and reached sexual maturity earlier. These factor most probably contributed to the observed disparity in population size between these two frog wherein R. cancrivora is about six times more numerous than R. limnocharis.

The fact that adult of these two species differ in size is also the main reason as to why they can coexist in the same habitat. Different body sizes allow them to ingest different sized prey items, as was discovered by analysis of their diets thus avoiding competition for food. Survivorships from eggs to metamorphosis for both species are low but normal for lentic-water breeding amphibian, and they are deemed sufficient to maintain the population levels if human interference can be substantially reduced. Fluctuation in the population structure mainly due to recruitment natural mortality and human interference. The most important food items for both species are insects and about 80% of these insects are pests of rice. Hence these frog are considered important biological control organisms in the paddy field habitat. Similarly in a very preliminary survey, birds are also potential biocontrol agents or bioregulators.

Concurrent toxicity studies indicated deleterious effects of the widely used insecticide, Carbofuran, on embryonic development resulting in teratogenic malformations of these two species of frogs.