Fruit choice and seed dispersal of invasive vs. noninvasive Carpobrotus (Aizoaceae) in coastal California

Natural hybridization between previously allopatric plant species can produce highly successful lineages. However, the ecological processes controlling the spread of hybrid genotypes have rarely been studied in the field. We compared fruit characteristics, fruit preference, and seed dispersal by native frugivores among the non-indigenous succulent Carpobrotus edulis, the putative native congener C. chilensis, and the hybrids resulting from introgressive hybridization. In this system, the non-native C. edulis and hybrids are known to be very successful invaders of California coastal plant communities. Carpobrotus edulis and hybrids produced more fruits per clone than C. chilensis, primarily as a consequence of larger clone size. Clone size and energy content of fruits were good predictors of fruit removal. Marked fruits of C. edulis and hybrids were removed faster than those of the other morphotypes, and C. edulis fruits were preferred over those of C. chilensis in a fruit transplant experiment. However, total fruit removal by the end of the growing season was very high for all morphotypes. Scats from black-tailed jackrabbit (Lepus californicus) and mule deer (Odocoileus hemionus), the most common frugivores in our sites, contained more seeds from C. edulis and hybrid morphotypes than from C. chilensis, and more than would be expected based on relative fruit abundance. Germination of seeds from C. edulis and hybrids was enhanced after gut passage, whereas germination of C. chilensis decreased after gut passage, compared to seed germination from intact fruits. The results suggest that patterns of fruit preference by native frugivores and seed survival after gut passage facilitate the successful spread of an aggressive introduced species and hybrids in contrast to the less aggressive, apparently native congener.