Regional and seasonal differences in movement patterns, rather than seasonal diet changes, determine seed dispersal by Asian elephants (Elephas maximus)

The impact of elephants in their habitats has been emphasized on ground of their large size and herbivorous behavior. However, as megaherbivores Asian elephants fulfill the conditions to be effective seed dispersers, with distinct functional attributes within seed dispersal networks. In southern Sri Lanka dry season enforces elephants to change their movement patterns and their diets, to items of higher fiber content and lower digestibility, which are expected to affect the gut retention time of dispersed seeds. To assess the spatial scale at which elephants can disperse the seeds we manipulated food quality of five elephants at Ueno Zoo (Tokyo) to provide them with rich (increased fiber, decreased digestibility) and poor (the opposite) diet and then assessed the retention time and survival of known amount of tamarind seeds ingested within intact pods. To estimate dispersal distance distributions, we combined these data with radio tracking data of Asian elephants from Sri Lanka (dry monsoon forest) and Myanmar (rain forest). Preliminary results show that maximum dispersal distance is usually less than 6 km, without seasonal differences. Increased gut passage time resulted in a lesser but faster germination, but we found no effect of diet changes on seed survival to gut passage, gut retention time, or germination. Variation among individual elephants, sometimes related to body size (e.g. for seed survival and retention time) had stronger effects than all above-described variables. However, the resulting dispersal distance distributions after combining all the variables reflected different seasonal patterns of seed dispersal at Myanmar and Sri Lanka.