A NULL MODEL TO STUDY COMMUNITY STRUCTURE OF MICROCRUSTACEAN ASSEMBLAGES IN NORTHERN CHILEAN SHALLOW LAKES

The inland water bodies of northern Chile (18-27 degrees S) are characterized by high salinity levels and impoverished species richness. This study presents field observations of species associations sampled from shallow water bodies in the Antofagasta region of northern Chile (23 degrees S). A species presence-absence matrix was created for calculating the Jaccard Index of community similarity and for testing null models of species associations, with the aim of determining whether species associations are random or not. The results of the Jaccard Index calculations indicated the existence of defined groups, including three sites with Artemia franciscana, two sites with Boeckella poopoensis, and a sixth site only containing the ostracod Sarscypridopsis aculeata. The results of the null model analysis denoted the presence of regulating factors only in fixed-fixed simulation, that is the most robust in comparison to the other two simulations that denoted absence of regulator factors in species associations. The Jaccard indices and significant null model analysis agree with previous ecological descriptions of salinity as a determinant of species associations, whereas the non-significant results of the other two simulations could be due to the low number of species reported. The ecology and biogeography of these communities are also discussed