FITNESS OF INVASIVE CARPOBROTUS (AIZOACEAE) HYBRIDS IN COASTAL CALIFORNIA

Natural hybridization between previously allopatric plant species can produce highly successful lineages. We test the low-fitness-hybrid hyp othesis in Carpobrotus and its implications for hybrid invasion. We ex amine reproductive fitness components of hybrids between the invasive non-native succulent Carpobrotus edulis (L. Bolus) and the non-invasiv e putative native C. chilensis (L.) from three populations in Californ ia coastal plant communities. Hybrids between the two species are very abundant and aggressive but it is not known if this is a transitory p henomenon. We find no support for the low-fitness-hybrid hypothesis in Carpobrotus. Fruit weight and seed set, mass and germination rate of hybrids were intermediate between or the same as a parental taxon. Sur vival, growth, and root to shoot ratio of hybrid seedlings did not dif fer from those of parental taxa. Although hybrid fitness is nor superi or to that of parental species, we believe that hybrids will continue to persist and invade California coastal communities because recruitme nt of seedlings did not differ from those of parental species. The hig hest survival probability of the introduced C. edulis may insure its s uccessful invasion status compared to the putative native congener C. chilensis.