The disruption of plant-animal interactions such as seed dispersal is one of the most critical effects of biological invasions. To understand the role of introduced species in current seed-dispersal systems, we conducted fecal analyses of the most common resident land birds on the Bonin Islands, Japan, and estimated their relative importance as seed-dispersal agents. Two native birds, the brown-eared bulbul and the Bonin Islands white-eye, and the introduced Japanese white-eye were the primary seed dispersers in secondary forest sites. Because the seed species composition in the feces of native and introduced white-eyes was similar, the latter may be replacing the former as a seed-dispersal agent. Introduced plants did not decrease the number of seeddispersal opportunities for native species through competition for seed dispersers. Because some bird species have already become extinct on the Bonin Islands, their ecological functions may also have been permanently lost; however, the introduced white-eye may be compensating for this loss of function. In addition, new mutualistic relationships involving native and introduced birds and plants have already been established. In order to control introduced species while having the least impact on the native biota, interspecific interactions must be thoroughly understood before initiating control efforts.
Impact of pollinator shift on differentiation of floral morphology has attracted the interest of naturalists for many years. A comparative investigation was conducted for determining the pollination characteristics, including pollinator assemblage, floral morphology, flowering phenology, and self‐compatibility, of two closely related Clerodendrum species—insular C. izuinsulare and widespread C. trichotomum. Japanese black swallowtail butterflies were the predominant flower visitors in mainland Japan, whereas diurnal hawk moths were predominantly found on the Izu Islands, a chain of oceanic islands located off the southeastern coast of the main Japanese island of Honshu in the west Pacific Ocean. The corolla tube of C. izuinsulare was longer than that of C. trichotomum, whereas the filaments and petals of C. izuinsulare were shorter than those of C. trichotomum. The flowering season of C. izuinsulare was later than that of C. trichotomum. The self‐compatibility of C. izuinsulare was higher than that of C. trichotomum. These differences might be associated with the low density of Japanese black swallowtail butterflies and dominance of diurnal hawk moths on the Izu Islands.
The microsatellite markers described here will be useful for comparative study of the reproductive systems and genetic structures of the narrow endemic C. izuinsulare and the widespread C. trichotomum.
Arnica mallotopus Makino is a perennial herb of Asteraceae endemic to Honshu and its adjacent islands in Japan (Ohashi et al., 2016). The species occurs preferentially on rock outcrops along mountain streams that are well watered by snowmelt and are often maintained by natu-
The division of labor between florets responsible for reproduction and special functions occurs widely in condensed inflorescences. The capitulum of Albizia julibrissin consists of approximately 10–20 lateral flowers and usually one nectar‐secreting terminal flower; the two flower types are morphologically distinct, but the differences in reproductive function have not been revealed. To determine the differences in reproductive function between terminal and lateral flowers, we compared the ratio of terminal and lateral flowers at the flowering and young pod stages. Additionally, ovule number, stigma size, polyad size, and the ratio of flower abscission were compared between the two flower types. Significant differences were detected only in female fertility between the two flower types. At the flowering stage, 6.8% of flowers were terminal flowers, whereas at the young pod stage, all young fruits were obtained from lateral flowers. At the final stage of blooming, based on the generalized linear model analysis, the ratio of surviving terminal flowers was lower than that of the lateral flowers in a capitulum. These results suggest that the terminal flowers of A. julibrissin had female sterility or, at least, female fertility was lower than in lateral flowers. Therefore, it is necessary to reexamine some previous studies that assumed A. julibrissin to be andromonoecious with hermaphroditic terminal flowers and male lateral flowers. Further comparisons of the quality of ovules and polyads are necessary to clarify whether there is a division of labor between the terminal and lateral flowers in A. julibrissin.
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