HYBRID VIGOR FOR CLONAL GROWTH IN CARPOBROTUS (AIZOACEAE) IN COASTAL CALIFORNIA

One of the consequences of the human-caused movement of plant species around the globe is hybridization between previously allopatric specie s. Introgressive hybridization between the non-native, invasive perenn ial succulent Carpobrotus edulis and the putative native, non-invasive C. chilensis is occurring throughout coastal California, leading to a high abundance of aggressive hybrid morphotypes and the loss of open space for native species establishment and growth. We test the hypothe sis that hybrid vigor for vegetative growth and resistance to herbivor y contributes to successful invasion by hybrid morphotypes, We compare d survival and vegetative growth of transplanted cuttings of three mor photypes (parental species and hybrids) in three habitats in a factori al watering and caging experiment. Overall Carpobrotus growth was both water and herbivore limited. Hybrids displayed higher growth than eit her parental species. Hybrids always had higher survival in response t o herbivory than C. chilensis, but survived better than C. edulis only in the bluff scrub. Growth of hybrids was higher than C. chilensis in the backdune and grassland but only higher than C. edulis in the back dune. Carpobrotus chilensis had the lowest survival to herbivory and t he slowest growth. Our data suggest that greater resistance to mammali an herbivory coupled with hybrid vigor for vegetative growth can contr ibute to the invasive status of hybrids. High susceptibility to browsi ng and slow growth of C. chilensis at least partially explain its non- aggressive nature in coastal California.