Significance of seed dispersal by the largest frugivore for large-diaspore trees

Abstract

How do large-bodied frugivores contribute to seed dispersal of large-diaspore plants? This study examined seed dispersal effectiveness for two large-diaspore tree species, Astrotrichilia asterotricha (AA) and Abrahamia deflexa (AD), in a Madagascan forest. I evaluated fruit removal rates through focal tree observations and factors affecting seedling recruitment up to the 2-year-old seedling stage. I confirmed brown lemur (Eulemur fulvus) as the sole disperser, removing 58.8% and 26.0% of fruits produced by AA and AD. Brown lemurs frequently visited large-crowned AA trees with high density of fallen fruits and more adjacent fruiting trees during seasons with low fruit diversity. Most AA seedlings were removed by predators, although canopy openness slightly improved seedling establishment. Although AD seeds were severely attacked by predators under mother trees, the seedlings survived under dispersal conditions distant from the mother trees, and with low density of diaspores. AD had a higher cumulative probability from fruit removal to seedling recruitment (6.5%) than AA (1.5%) in the first rainy season. This study clarifies the significance of seed dispersal to tree recruitment strategies, which vary among different combinations of tree species and large frugivores, i.e. quantitative dispersal to reach suitable microhabitats, and qualitative dispersal to escape from dangerous zones near mother trees.