Frugivore loss has the potential to alter the regeneration of tropical hyperdiverse forests. However, no study has investigated tree diversity maintenance within old-growth protected forests on tropical oceanic islands where conservation stakes are considerable. In the Mascarenes, the largest frugivores including the Dodo went extinct after human colonization in the 17th century. Mauritius, today devoid of almost all its native habitats, retains an important population of flying foxes, while Réunion, largely covered by native habitats, has lost all but one of its native frugivores, a bulbul. Using census data of 130 woody species from 3-ha permanent plots from Mauritius (MAU-BF) and Réunion (REU-ML), we show that most fleshy-fruited species regenerate well at MAU-BF, in contrast to REU-ML, although large-seeded fleshy-fruited species regenerate poorly at both sites. The difference in recruitment is all the more striking because local woody plant diversity at MAU-BF is double that at REU-ML. Changes observed in the understory will probably lead to a strongly impoverished canopy at REU-ML, and to canopy shift composition at MAU-BF. Hence, the protected but highly fragmented forests on Mauritius are likely more resilient than those on Réunion usually considered best preserved within the ecoregion. Although processes other than seed dispersal might also be at work, flying foxes probably ensure effective dispersal of numerous native fleshy-fruited plants on Mauritius, contrary to only bulbuls on Réunion. To efficiently protect tropical rainforests on islands and continents alike, there is an urgent need to protect extant frugivores populations and reinstate seed dispersal function wherever necessary.