Earthworm communities in native savannas and man-made pastures of the Eastern Plains of Colombia

Abstract

The structure and seasonal changes of earthworm communities were evaluated in a natural Savanna and in an introduced grass-legume pasture in a Colombian oxisol over a period of eighteen months. One plot of 90x90 m was isolated in each of the systems and each month five samples of 1m 2 x 0.5 m and 10 of 20x20x20 cm were randomly selected from a stratified block design. Species richness was similar in the two evaluated plots (7 species), whereas diversity H' index (Shannon and Weaver, 1949) was clearly different, 2.89 in natural Savanna and 1.29 in pasture. This is explained by differences in earthworm community structure. Average annual density in Savanna was 49.8, ranging from 10.8 to 135.8 ind. m -2 , and biomass was 3.3 g m -2(hand-sorting method), ranging from 0.9 to 11.5 g m -2 . In the man-made pasture, density was 80.1 ind m -2 on average, ranging from 24 to 215.8 ind m -2 and biomass was more than tenfold higher, ranging from 29.2 to 110.4 g m -2 . This was especially due to the presence of a large glossoscolecid anecic species, Martiodrilus carimaguensis n. sp.(Jiménez and Moreno, in press), which has been greatly favoured by conversion of savanna to pasture. Endogeic species were dominant in the natural Savanna whereas the anecic species accounted for the 88% of total earthworm biomass in the pasture. Figures of total earthworm density and biomass were significantly different in the two systems studied (t-test). The results indicate a clearly positive response of earthworm communities to improved pastures, a type of land use that is increasingly adopted in moist neotropical savannas.3

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

“…Two patches could be observed, one of them large placed on the left side of the plot and the other one located at the right corner somewhat smaller than the former. By June 1995 the whole population was made up of juveniles, since adults begin to appear at the end of the rainy season (Jiménez et al, 1998b). It was as if the large patch would have moved to the left and in the right corner two new patches were distinguished.…”

“…Hairston (1959, quoted in Lloyd, 1967 concludes that aggregation indices are higher for rare species and Andiorrhinus sp. is a rare species in Carimagua (Jiménez et al, 1998b).…”

“…In the investigated paddocks, the earthworm community is comprised of eight species, all natives and present in the introduced system (Jiménez et al, 1998b). Most species belong to family Glossoscolecidae, the most widespread earthworm family in the neotropical region, Andiodrilus sp.…”

“…3.26 g fresh weight per m 2 , Glossodrilus sp. being the most abundant species, whereas in the pasture, several endogeic species represent only 12% of the total earthworm biomass, 57.1 g fresh weight m 2 , and the anecic species accounts for 88% of total biomass (Jiménez et al, 1998b).…”

Spatial dissociation between two endogeic earthworms in the Colombian “Llanos”

“…The main biology and ecology of each species is precisely described in [9]. This study mainly focused on the relationships between two endogeic species that dominate the community in terms of density, i.e.…”