Spatial distribution of earthworms in acid-soil savannas of the eastern plains of Colombia

The horizontal spatial distribution of earthworms in a native savanna and i n a 17 year introduced pasture from the area of Carimagua (Colombia) was as sessed by means of aggregation indices and geostatistical analysis. Morisit a's index (Id) and Taylor's index (b) were calculated from field data obtai ned through Im? quadrats during a sampling period of 17 months and both sem ivariograms and contour maps were obtained at three different dates through a rapid sampling of 64, 40 cm x 40 cm x 15 cm soil blocks, regularly distr ibuted in the nodes of a 8 x 8 grid (i.e. 70 m x 70 m). Earthworms tended t o exhibit contagious distribution in both land use systems and a multivaria te relationship appeared between the size of the earthworm and aggregation indices employed. Land use had no significant effect on the spatial distrib ution of earthworms. Earthworms belonging to different ecological categorie s and from diverse sizes were spatially distributed in patches of several t ens of meters. Semivariograms reflected, occasionally, the size of these pa tches, although, no spatial structure was perceived at some dates. This mig ht be due to the intersample distance employed (10 m) so that changing the scale of observation could reflect unseen patterns. In this study our purpose was first to determine the strength of spatial ag gregation in some Neotropical earthworm species and then to observe the mov ement of population patches at the scale of the studied area. The use of th ese types of spatial analyses in conjunction may be very useful to establis h the dynamics of earthworm populations in the field. (C) 2001 Elsevier Sci ence B.V. All rights reserved.