The type of egg production curve with respect to population preservation: Ecological studies of tadpole shrimps (Branchiopoda: Triopsidae) for the biological control of weeds in rice paddies

Summary

Tadpole shrimps, Triops spp., are aquatic pioneer animals in a desert environment and have a life cycle adapted to irregularly disturbed habitats. The effect of rearing density was examined on the survival, growth of carapace length, and egg production of T. cancriformis under the experimentally controlled condition at 21–22 °C of water temperature. The skewed shape of egg production curve suggests a violent fluctuation in the population of homogeneous age structure, which is not acceptable for the practice of biological control of paddy weeds. However, all eggs do not hatch at once after water submergence but some parts are carried over to subsequent generations as dormant eggs. This heterogeneous hatching has the big effect of stabilizing the population fluctuation. On the other hand, the heterogeneous age structure prepared in a population has also the effect of modifying the shape of the egg production curve to a saturation type suggesting a stable and enhanced population.

For the maintenance of stable populations in rice fields soft puddlings and intertillages are recommended to carry over the eggs to subsequent generations and ensure hetergeneous age structures in the shrimp population.