| Much debate surrounds the question of which breeding system is favored in the establishment of oceanic island floras. The breeding strategies of 52 representative Galapagos Islands angiosperms from 30 families were examined. Controlled pollinations were performed to determine if self-incompatibility was more prevalent than previously thought, thus acting as an enforcer of outcrossing, or if instead, both dioecism and self-incompatibility are poorly represented and self-compatibility is the rule. Viability studies were performed to determine if seeds produced by crossing or selfing had any superiority in this respect. Obervations of flower visitors were also undertaken to determine their importance as potential pollinators.; The plants tested were located in each of the seven major vegetation zones on the southern slope of Isla Santa Cruz. Fruit and seed yields were compared between tagged but untreated flowers (controls) and others that were subjected to various treatments. Of the 52 species studied, one was dioecious, 11 yielded inconclusive results, and the remaining 40 showed self-compatibility. All but three of the latter group also demonstrated automatic self-pollination. Viability results showed no difference between seeds produced by crossing versus those produced by selfing. The endemic carpenter bee, which is polylectic and visits many different plants for pollen and nectar, continues to be the major pollinator on Santa Cruz, however, nine other insects are newly reported as flower visitors. Twenty-two of the plant species studied represent new records of flower visitation by insects other than the carpenter bee on this island. In general, plants were visited by the few insects available, regardless of flower color, or were not visited at all.; The results of this study indicate that on the Galapagos Islands there has been neither a selective drive toward evolution of dioecism nor are dioecious plants inordinately favored in establishment. Instead, hermaphroditic and dioecious plants occur in relatively the same proportions as found in their mainland source areas. Of the two hermaphroditic breeding strategies considered in this study, self-compatibility and self-incompatibility, the former is highly represented in the Galapagos flora. |
