APPLE SNAIL (POMACEA-DOLIODES) AND FRESH-WATER CRAB (DILOCARCINUS-DENTATUS) POPULATION FLUCTUATIONS IN THE LLANOS OF VENEZUELA

From July through November 1988 and 1989, apple snail (Pomacea doliode s) and freshwater crab (Dilocarcinus dentatus) populations were survey ed in rice plantations and seasonal wetlands (or ''esteros'') in the l lanos of Venezuela to determine seasonal changes in density and size. Rice plantation sites had significantly higher densities and larger sn ails than did estero sites. Snail density did not differ significantly between months or years. In contrast, the density and size of freshwa ter crabs varied significantly by month but not between habitats or ye ars: crabs were smaller and in greatest numbers at the beginning of th e rainy season, and then declined in density but increased in size by November. The sex ratio of D. dentatus was skewed towards females, a r atio which was consistent across habitats and months. Fluctuations in snail and crab density and size are discussed in relation to the effec ts of wetland flooding regimes on the life history characteristics of these animals.