Animal movements and behavior shape the spatial patterns of seed dispersal for up to 80% of tropical tree species. The movements of social versus non-social frugivores can have important spatial consequences for both long-distance and aggregated seed dispersal across landscapes. We tested hypotheses regarding the effects of sociality on seed dispersal for two species of sympatric toucans in Costa Rica. Because foraging groups of animals exhaust fruiting resources more quickly than individuals, we predicted that a social toucan species, the collared araçari (Pteroglossus torquatus), would move more often and travel longer distances, resulting in increased long-distance dispersal and less clumped aggregation of seeds (mean distance of seeds from each other) than a non-social species, the keel-billed toucan (Ramphastos sulfuratus). We collected data on movement distances and time between movements by radio tracking 9 keel-billed toucans and 13 collared araçari social groups in a fragmented forest landscape in Turrialba, Costa Rica over a 16-month period. We also conducted toucan gut passage trials for three tree species, two with larger seeds (8mm, 12mm) and one with smaller seeds (1mm). Using these data, we parametrized a spatially-explicit, individual-based model to test our predictions and compare long-distance and aggregated dispersal for both toucan species.
Results/Conclusions
Time between movements and gut retention times were similar for both species, but keel-billed toucans exhibited 30% higher movement distances, contrary to our predictions. Both toucan species dispersed seeds of all three tree species long-distances (>100 m) from parent trees; however, keel-billed toucans dispersed seeds from 4-15% further than collared araçaris on average, contrary to our predictions. Results for aggregated seed dispersal partially supported our predictions. Keel-billed toucans dispersed the two larger seed species 23-48% further from each other than collared araçaris. However, collared araçaris dispersed the smallest seed species approximately 11% further from each other than keel-billed toucans. Our modeling approach indicated that these results were influenced by the behavior of each species and interactions with the fragmented landscape, potentially explaining differences in our results from previous studies.