The island of Puerto Rico is home to five species of columnar, globular and semi-epiphytic cacti: Pilosocereus royenii, Melocactus intortus, Stenocereus fimbriatus, Leptocereus quadricostatus and Hylocereus trigonus. However, their ecology and natural history are still largely unknown. We visited a total of 12 sites during four years. We identified habitat preferences for each cactus species; recorded the incidence of fires and the invasion of grasses in these habitats. We also recorded bird-cactus interactions during 150 hrs. of observation. Observations on the reproduction biology of S. fimbriatus is provided for the first time, and differences of M. intortus morphology of two populations were assessed. Finally, we identify different threats to the Puerto Rican native cacti and dry forests. We also identified various questions on the basic ecology and biology of these cactus species that should be addressed in future works.