Linking spatial patterns of seed dispersal and plant recruitment in a neotropical tree, Virola calophylla (Myristicaceae).

摘要

Seed dispersal establishes the initial spatial template upon which demographic processes are played out to produce spatial structure in plant populations. The objective of this investigation was to develop a thorough understanding of the spatial pattern of seed dispersal, the factors affecting it, and its recruitment implications in an animal-dispersed tree species, Virola calophylla (Myristicaceae), in the Peruvian Amazon. Although 17 bird species dispersed V. calophylla seeds, one primate species (the spider monkey, Ateles paniscus) dispersed 92% of all dispersed seeds. Dispersal agents responded differently to some tree and fruit traits, indicating that dispersal agents can exert selection on traits affecting seed dispersal, but that the resulting selection pressures are likely to be inconsistent. To quantify landscape-scale seed dispersion, a mechanistic model was developed that simulates the spatial stochastic process of seed dispersal. Spatial variation in seed density was significant, being highest underneath female V. calophylla parents and at the sleeping sites where spider monkeys defecated seeds. An examination of the recruitment consequences of this spatially restricted seed deposition demonstrated strong density- and distance-dependent seed survival. Nonetheless, seedlings and saplings were concentrated where seed-fall was greatest and showed significant clumping. Therefore, the initial pattern of seed deposition was largely maintained through regeneration to the sapling stage and was consistent with adult dispersion. Clumped recruitment patterns arose even in the presence of strong distance- and density-dependence, suggesting that restricted seed dispersal has a dominant effect on the spatial structure of this population of V. calophylla.