Seed dispersal is a key process that drives forest diversity and genetic structure. Theoretical and empirical evidence point to the advantages to plant recruitment of escaping density- and distance-dependent mortality by having seeds removed from vicinity of the maternal plant. Further, long-distance dispersal events are thought to be particularly important in population spread, colonization, and gene flow between populations. In tropical wet forests, most trees rely on animals to disperse their seeds. Yet, despite this, for some plants relatively few species are responsible for a disproportionate number of seeds removed from maternal plants. In our Amazonian study system, Virola flexuosa, a canopy tree, is primarily dispersed by toucans and araçaris (Ramphastidae); approximately 65% of visits and 52% of dispersed seeds are removed by these birds. Consequently, movement patterns of these birds directly influence the spatial dispersion of seeds and shape population structure and dynamics. Previous work generated Virola seed dispersal kernels and estimated dispersal distances using information from population means integrated across data that combined animal movement distances with seed passage times. Here we ask how individual variation in animal movement impacts Virola seed dispersal using individual-based models to generate spatially explicit seed dispersal kernels.
Animal movement data, including home ranges, movement rate, and distances moved within a time period most likely to result in passage of Virola flexuosa seeds were examined for 12 individuals of Pteroglossus pluricinctus, the many-banded araçari, based on radio-telemetry data. Home range sizes and movement rates varied considerably among individuals, as did the actual distances moved in either 15-min or 30-min time period, the period of time most relevant to predicting seed dispersal distances. Body size and reproductive activity influences animal movement patterns and, consequently, seed dispersal patterns. Individual variation in movement and behavior were included as estimated parameters from empirical data for the simulations in our model. Comparing the output of seed deposition patterns from our model to effective seed dispersal distances allowed us to identify the relative influence of variation in specific individuals on long-dispersal events and overall seed deposition patterns. Understanding how and why animals vary in key behaviors that influence seed removal and seed dispersal is needed to better evaluate the consequences for plant recruitment and plant population dynamics.