Probabilistic models and contingency tables for studying potential species interactions between two intertidal decapods in the north of Chile (Cifuncho, 25°S, Antofagasta region, Chile)

Abstract The northern Chilean coast is characterized by its high productivity and diversity due to the presence of the cold, nutrient-rich water of the Humboldt Current. In this scenario, the rocky shore provides many microhabitats for invertebrates such as crustaceans. The aim of the present study was to analyse potential species interactions using probabilistic models and contingency tables. In this particular case we analysed the potential interactions between two sympatric intertidal decapods, Cyclograpsus cinereus and Petrolisthes granulosus , on the rocky shores of Cifuncho Bay, an isolated bay in the north of Chile. The results revealed that both species had a uniform pattern, that was adjusted to a binomial distribution for C. cinereus , and a Poisson distribution for P. granulosus . These results are probably due to territorial behaviour, and this was corroborated by the results of the contingency table, which denoted the independence of both species. These results would not coincide with classical observations of intertidal decapods on rocky shores of continental Chile, as those denoted a gregarious pattern. However, on the other hand, the present results do not explain any details about potential interactions between the two species here analysed.