Co-occurrence of earthworms in urban surroundings: A null model analysis of community structure

Diamond's assembly rules predict that competitive interaction between species lead to a non-random co-occurrence of patterns. Earthworms were sampled in five lawns of Roosevelt Avenue (city of Brussels, Belgium) to test the reduced level of co-occurrence of species among earthworm communities. We used null model to generate patterns expected in the absence of species interactions. With the model algorithm that maintains fixed row sums and fixed column sums, species co-occurrence in two out of five islets (5 and 10), was less than the expected; whereas in islets 3, 8 and 9, species assemblage seemed random. This study indicates that the non-random selection observed in the two lawns is because there is an interaction between species close to the same ecological category.