A biogeographic approach to the insular marine 'prosobranch' gastropods from the southwestern Atlantic Ocean

The MacArthur & Wilson theory of island biogeography predicts that the balance between immigration and extinction rates results from the size and degree of isolation of the island. Here, we test this assumption using data from the marine gastropods of Brazilian oceanic islands. Species lists were compiled for Rocas Atoll, the Fernando de Noronha Archipelago, the Sao Pedro and Sao Paulo Archipelago and Trindade Island. These were compared with the predictions of the theory based on the shallow platform area and distance from the mainland (Model 1) and the nearest reef habitat (Model 2). Results corroborated at least in part the assumptions proposed by MacArthur & Wilson. Sao Pedro and Sao Paulo and Fernando de Noronha fitted the equilibrium model of extinction and immigration rates, while Trindade and Rocas Atoll stood out as an exception to Model 1 and to Models 1 and 2, respectively. The relevance of the age of the island and presence of seamount chains is discussed to explain this discrepancy.