Population dynamics and adaptative strategies of Martiodrilus carimaguensis (Oligochaeta, Glossoscolecidae), a native species from the well-drained savannas of Colombia

#Martiodrilus carimaguensis$ (Oligochaeta, Glossoscolecidae) is a large, anecic native earthworm species which was found in natural and disturbed savannas in the Oxisols of the Colombian Llanos. Its population dynamics were studied in a native savanna, and in a 17 year old grazed grass-legume pasture where density and biomass were higher. Monthly cast deposition on the soil surface in the improved pasture was 38.4 x 10(exp 3) fresh casts/ha, eleven times more than in the native savanna. A strong relationship was found between numbers of #M. carimaguensis$ and numbers of fresh surface casts. Different patterns of adaptation to the dry season were observed for adults and juveniles. Adults are active for eight months whereas juveniles enter diapause 3-4 months earlier. The vertical distribution pattern of the earthworm population also shows marked seasonal changes. (Résumé d'auteur