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Fruit Removal and Seed Predation in Two African Trees (Lannea acida and Lannea welwitschii, Anacardiaceae)
Abstract
Fruit removal is an important component of plant fitness. The role of different frugivores in removal efficiency of two small-fruited trees, Lannea acida and L. welwitschii (Anacardiaceae), at Comoé National Park, northeastern La Cote d’Ivoire was investigated. At least 12 bird species, the red-legged sun squirrel (Heliosciurus rufobrachium), and four primate species consumed the fruits of the L. acida focal tree. Crop removal efficiency varied between 21% and 30% in two consecutive years. Up to 100% of the harvest and fruit fall were unripe fruits. Removal efficiency in L. welwitschii was higher (48.5%) despite lower visitation rates and only two
species observed feeding. Most L. welwitschii fruits were removed during and after maturation but predispersal seed predation by H. rufobrachium left only 19.9% of the total crop to potential seed dispersal. In contrast, H. rufobrachium rarely fed on L. acida seeds. Sun squirrels consumed about twice (L. acida) to 10 times as much (L. welwitschii) fruits (seeds) per visit than birds. Primates removed 20-30 times more L. acida fruits and about 30 times more L. welwitschii fruit per visit than birds, but birds are able to compensate for lower food intake per visit by visiting a feeding tree more frequently. Birds and primates may, thus, both be important seed dispersers of Lannea seeds in terms of quantity. As a consequence of a large amount of unripe fruit fall and high pre-dispersal seed predation by vertebrates, the reproductive output of the focal trees during the study period in terms of dispersed seeds was low. Regeneration in L. acida and L. welwitschii might, thus, be source limited and dissemination limited, at least in certain years. Because interannual and intraspecific variation in fruit removal can be substantial, further research is required to determine long-term reproductive output in the two species.
species observed feeding. Most L. welwitschii fruits were removed during and after maturation but predispersal seed predation by H. rufobrachium left only 19.9% of the total crop to potential seed dispersal. In contrast, H. rufobrachium rarely fed on L. acida seeds. Sun squirrels consumed about twice (L. acida) to 10 times as much (L. welwitschii) fruits (seeds) per visit than birds. Primates removed 20-30 times more L. acida fruits and about 30 times more L. welwitschii fruit per visit than birds, but birds are able to compensate for lower food intake per visit by visiting a feeding tree more frequently. Birds and primates may, thus, both be important seed dispersers of Lannea seeds in terms of quantity. As a consequence of a large amount of unripe fruit fall and high pre-dispersal seed predation by vertebrates, the reproductive output of the focal trees during the study period in terms of dispersed seeds was low. Regeneration in L. acida and L. welwitschii might, thus, be source limited and dissemination limited, at least in certain years. Because interannual and intraspecific variation in fruit removal can be substantial, further research is required to determine long-term reproductive output in the two species.
