Project: Comparison of seed predation and the effect of secondary dispersal on the seed dispersal effectiveness of the last two megafrugivores of the Atlantic Forest, the muriqui (Brachyteles arachnoides) and the tapir (Tapirus terrestris)

 

Abstract: Seed dispersal by animals is a key process for the maintenance and dynamics of tropical forests. It allows plants to escape distance-dependent mortality from the parent tree, to colonize new habitats and to find suitable microhabitats for its development. In tropical forests, seed dispersal is often done in two phases (diplochory) called primary and secondary dispersal. In tropical areas, primary dispersal by endozoochory followed by secondary dispersal by dung beetles is a common process. Therefore, after the defecation of seeds by a frugivore, dung beetles, attracted by the fecal matter, will bury the seeds at different depths that can protect them against seed predators but also promote or inhibit their germination. To quantify the success of seed dispersal and easily compare it under different contexts, we used the concept of seed dispersal effectiveness (SDE). The SDE is determined by two components: a quantitative one that is the number of seeds dispersed, and a qualitative one that is the probability of seedling emergence or probability of survival. However, post-dispersal events including secondary dispersal by dung beetles and seed predation are rarely taken into consideration when calculating SDE. We determined the probability of predation and survival of seeds dispersed by the two last neotropical megafrugivores of the Brazilian Atlantic Forest, the muriqui (Brachyteles arachnoides) and the tapir (Tapirus terrestris), at different burial depths in order to obtain the data needed to calculate SDE. We combined our data with those collected in previous studies about the quantitative component of SDE and the probability of seed burial by dung beetles. Seed predation did not differ between muriquis and tapirs’ feces. The probability of seed predation decreased with increasing depth and seed size in both feces. However, the burial depth increased seed mortality rate. Secondary dispersal had positive or negative effects depending on seed species, burial depth, and the primary disperser (muriqui or tapir). Finally, our results showed that the tapir is a better disperser for Vantanea compacta than muriqui. These results lead us to conclude that these two frugivores have complementary roles in seed dispersal and that we need to understand the selective forces acting on fruit and seed characteristics as well as on plant-animal interactions in order to maintain these ecologically important relationships, given the accelerating species decline.

 

 

 

 

 

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