Seed dispersal of Madagascar's iconic baobab species, Adansonia grandidieri

Abstract

Certain plant species have traits adapted for seed dispersal by megafauna, which may be absent in their current ranges. Characterizing the dispersal mechanism of such plant species can provide insights about their population dynamics and regeneration. We investigated the effectiveness of the extant fauna as seed dispersers of the Malagasy baobab, Adansonia grandidieri, which have megafaunal dispersal traits. We documented the animal species that interact with its fruits and seeds in the canopy and on the ground through direct observations, camera trapping, opportunistic search of feces with seeds, and dispersal experiments. We also estimated seed fate using a model parameterized with data obtained through experiments on seed removal and seed germination under and away from adult A. grandidieri trees. Further, we examined the impacts of seed dispersal in mitigating herbivore pressures on A. grandidieri seedling through an exclosure experiment. We did not find animals interacting with fruits in the canopy. However, we observed a native rodent species, Eliurus myoxinus, handling fruits/seeds on the ground, and found seeds in bush pig feces. Also, while the rates of germination for the dispersed A. grandidieri seeds were low, their probability of producing viable seedlings was higher than when the seeds stayed under adult trees. We also found that the seedlings of A. grandidieri had a high probability of surviving even when herbivores were present. Overall, our results provide insights into the regeneration of A. grandidieri and suggest that some extant local ground-dwelling fauna can provide seed dispersal services to this species.

Abstract in Malagasy is available with online material.