M. Vila et Cm. Dantonio, FRUIT CHOICE AND SEED DISPERSAL OF INVASIVE VS. NONINVASIVE CARPOBROTUS (AIZOACEAE) IN COASTAL CALIFORNIA, Ecology, 79(3), 1998, pp. 1053-1060
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 s
eed 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, t
he non-native C. edulis and hybrids are known to be very successful in
vaders of California coastal plant communities. Carpobrotus edulis and
hybrids produced more fruits per clone than C. chilensis, primarily a
s a consequence of larger clone size. Clone size and energy content of
fruits were good predictors of fruit removal. Marked fruits of C. edu
lis and hybrids were removed faster than those of the other morphotype
s, 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. Seats from bl
ack-tailed jackrabbit (Lepus californicus) and mule deer (Odocoileus h
emionus), the most common frugivores in our sites, contained more seed
s from C. edulis and hybrid morphotypes than from C. chilensis, and mo
re than would be expected based on relative fruit abundance. Germinati
on of seeds from C. edulis and hybrids was enhanced after gut passage,
whereas germination of C. chilensis decreased after gut passage, comp
ared to seed germination from intact fruits. The results suggest that
patterns of fruit preference by native frugivores and seed survival af
ter gut passage facilitate the successful spread of an aggressive intr
oduced species and hybrids in contrast to the less aggressive, apparen
tly native congener.