Qualitative Aspects of Seed Dispersal Effectiveness by Mantled Howler Monkeys (Alouatta palliata mexicana): The Case of Three Species of the Moraceae Family

Howler monkeys are considered high-quality seed dispersers; however, the changes that seeds undergo after passing through their digestive tract, which influence their germination capacity, are still unknown. In this study, we assessed whether the consumption of seeds from three species of the Moraceae family by mantled howler monkeys results in seed coat scarification, and whether this treatment enhances their permeability to water and germination rate. Using seeds from fruits, we induced chemical scarification of their outer coat, and with these, intact seeds and seeds found in droppings, we conducted micromorphological analyses, water permeability tests and germination assays. We observed that the passage of seeds through the digestive tract of mantled howler monkeys did not scarify their outer coat, nor did it enhance their water absorption capacity. There was both a positive and negative effect on the germination of Ficus americana and Ficus insipida seeds, respectively. Chemical scarification of the seeds, although it reduced their coat thickness, did not increase water permeability, significantly decreased their viability, and prevented germination. These results suggest that, in the case of small seeds, scarification is not a relevant treatment for germination and may, in fact, be unfavorable. Therefore, the importance of seed consumption by mantled howler monkeys, and other frugivores, may lie in the removal of pulp in terms of the facilitation of germination. Thus, by moving, releasing and cleaning the seeds, these animals may increase the probability that they will encounter adequate environmental conditions for germination and establishment.