Habitat Duration and Dipteran Larvae in Tropical Rain Pools

The role of habitat duration in effecting the distribution of fly larvae in tropical rain pools is examined. Field observations over a complete rainy season show that the duration of each pool varies considerably in response to the pattern of rainfall. Pools of short duration (less than 1 wk) are occupied by Polypedilum vanderplanki or Dasyhelea thompsoni larvae which have physiological adaptations to desiccation. Larvae of a third species, Chironomus imicola which lack drought resistance only occupy the larger pools at the height of the rains when durations are extended to several weeks. As the rains diminish and durations become reduced, drought resistant D. thompsoni replace C. imicola larvae in certain pools. Experiments support field observations that the latter species is restricted to pools of long duration and reveal that the relatively stable water level in such pools adversely affects oviposition by D. thompsoni. The contribution of pool duration and other factors to the maintenance of a single species of fly larva in each pool is discussed.