One of the long-standing questions in ecology and evolution is whether species diversity is regulated in a steady state through time, and if so what factors determine the steady-state level. Oceanic archipelagoes are interesting and well-defined test cases for such questions. Here we used a two- stage approach to investigate the diversity of indigenous and endemic species of vascular plants, birds, land snails, and spiders of the 14 major volcanic archipelagos of the globe. First we used a regression framework to quantify classic macroecological descriptors such as total area, number of islands, isolation from continental masses, and latitude. Second, to disentangle ecological and evolutionary mechanisms underlying patterns identified during the first descriptive modeling step, we developed a process-based modeling framework in which species richness is a steady state outcome of underlying processes: anagenic and cladogenic speciation, extinction, and colonization. We demonstrate an unexpected parallel scaling of species richness across taxa despite great physiological and ecological differences. We show that this parallel scaling arises as a result of the similar effects of physical archipelagic characteristics on biogeographic rates across disparate taxa.