Seed dispersal, habitat selection and movement patterns in the Amazonian tortoise, Geochelone denticulata

Abstract

The Amazonian tortoise Geochelone denticulata may play an important role in forest dynamics due to its highly frugivorous diet, ability to disperse viable seeds, and predilection for resting in forest gaps for thermoregulation. The purpose of our study was to evaluate the species' effectiveness as a seed disperser. We measured dispersal quantity (abundance of seeds in feces, frequency of droppings, and population density of the disperser) and dispersal quality (movement patterns, habitat use, germination rates of dispersed seeds, and recruitment probabilities of seedlings) in a SW Amazonian forest, in Peru. Population density was calculated by mark-recapture and line-transect methods. Eight individuals were radio-tracked to monitor habitat use. Diet was described from fecal samples, which were washed to count seeds and for germination experiments. Seedling survival in different environmental conditions was monitored for three plant species. Population densities with mark-recapture estimates (0.15-0.31 individuals/ha) were much higher than with line transects estimates (0.0025 individuals/ha). Diet included fruit of 55 different plant species. Dispersed seeds had high germination rates (average 76%). In spite of their low activity, we documented long seed dispersal distances (average 89.6 m). Tortoises showed a marked preference for the open-canopy swampy forest, where long term recruitment was not favorable for seedlings of the species examined. However, the high solar radiation in this forest type promoted survival of pioneer seedlings in the short term. In conclusion, while G. denticulata did not perform a very efficient role in terms of the quantity of seed dispersal, the species can be considered efficient in many aspects of dispersal quality. © 2008 Koninklijke Brill NV, Leiden.