Fruit Choice and Seed Dissemination by Birds and Mammals in the Evergreen Forests of Upland Malawi
FRUIT CHOICE AND SEED DISSEMINATION BY BIRDS AND MAMMALS IN THE EVERGREEN FORESTS OF UPLAND MALAWI Françoise DOWSETT-LEMAIRE Rue de Bois de Breux, 194, B-4500 Jup ille, Liège, Belgique The study of interactions between fruit and their vertebrate consumers has generated a great deal of interest in recent decades. Most authors have investi gated the habits of single bird or mammal species ( e.g. Phillips, 1926, 1927, 1928 ; Frith, 1957 ; Snow, 1962 ; Gautier-Rion, 1971 ; Alexandre, 1978) or the assem blages of species - main1y birds - attracted to the fruits of particular trees (e.g. Land, 1963 ; Willis, 1966 ; Leck, 1969 ; Howe, 1977, 1981 ; Bronstein & Hoffmann, 1987). Studies of the fruit-eating behaviour of phylogenetically-related groups of consumers are fewer (e.g. Snow & Snow, 1971 ; Crame, 1975 ; Gautier-Rion, 1980 ; Beehler, 1983) and those dealing with a whole class of vertebrates such as birds are evident1y rare (Frost, 1980 - incompletely publis hed ; Herrera, 1984 ; Wheelwright et al. 1984). Noteworthy is the work by Gautier-Rion et al., (1985a) who analysed fruit choice in a large community of mamma1s (bats excepted) and seven large canopy bird species in a Gabon rain forest. Early models of plant-frugivore interactions have stressed the distinction between specialized, obligate frugivores that feed on, and disperse efficiently, high-quality fruits (with low and extended fruit production), and the unspeciali zed, opportunist feeders that take Jess nutritious fruits (with scattered, shorter seasons) (McKey, 1975 ; Howe & Estabrook, 1977 ; Snow, 1981). However, subsequent field work has largely failed to confirm these original predictions on diet specialization and dispersal quality ; most studies of birds have, instead, emphasized the tremendous diversity of frugivores at fruiting trees, even with high-reward fruits (e.g.
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