EARTHWORM COMMUNITIES OF TROPICAL RAIN-FORESTS

A comparative study of tropical rain forest earthworm communities was carried out to try to identify general patterns of organization. The study included 5 sites in Mexico and Central America, 3 in South America, 2 in Central and Western Africa and 2 in Southeast Asia. Data base comprised 15 biological variables and 11 climatic and edaphic variables. Average earthworm values of abundance and biomass were 68 ind m-2 and 12.9 g m-2 respectively, which were not very different to those values occurring in temperate woods; however, they were considerably lower when compared to temperate and tropical grasslands. Density and biomass showed a bell shape response in function of annual rainfall, with maximal values between 2000 and 4000 mm. Earthworms were mainly concentrated in the first 0-10 cm of soil depth. Two kinds of communities were differentiated: one dominated by litter-feeding epigeics and anecics and the other one by geophagous endogeics. The former group was associated to oligotrophic soils from South America and Africa, whereas the second one was characteristic of the rich, neutral soils of Mexico and Africa (one site). It is concluded that environmental variables, more than phylogenetic constraints, are the most important factors in determining the structure of these communities. Comparisons with other soil macrofauna groups revealed that earthworms are the most important group regarding biomass and rank third in terms of abundance. The importance of these organisms in the dynamics of tropical rain forest soils is discussed in terms of the kind of community found elsewhere.