PARENT SESSION
Symposium #4: Long-distance dispersal.
Sponsored by ESA Plant Population and Theoretical Ecology Sections
Organized by: R. Nathan, M. Cain, S. Levin.
Monday, August 6, 2001. 1:00 PM to 5:00 PM. Lecture Hall
Tapirs as long-distance seed dispersal vectors: implications for the survivorship and spatial distribution of tropical trees.
Fragoso, José1, Silvius, Kirsten1, 1
ABSTRACT- We simulated the landscape level seed dispersal dynamics generated by the lowland tapir (Tapirus terrestris) and supported the hypothesis of a qualitative difference between survival dynamics at local and landscape levels. Mature seeds of Attalea maripa without bruchid beetle eggs, larvae or adults were collected from whole-ripe fruit. Around 13 adult A. maripa we placed a paired treatment: 1) seeds in tapir feces and 2) bare seeds on the ground, both located within 5 m of a conspecific fruit dropping tree located in conspecific aggregations. We repeated the experiment by placing seeds in the two treatments within 5 m of 13 emergent forest trees (simulated tapir latrines) all located from 4 to 7 km from conspecific tree aggregations and reproductive age conspecifics. All treatments were covered with a protective cage and left in the forest for 7 months. Significant differences in survivorship were observed between seeds in feces around forest emergents (92 % survirorship) and seeds in feces around conspecific adults (61 %); and between bare seeds around emergent trees (75 % survivorship) relative to those around conspecific adults (9 % survivorship). The differences in survivorship between the site types were statistically significant, as were those between seeds in feces and in bare piles. The magnitude of difference between seeds in feces versus those left on the ground was not significant for the treatments located kms from conspecific aggregations, but was for the treatments within aggregations (61 % versus 9 %). Landscape level dispersal moved seeds away from conspecific aggregations and into new within-forest colonization zones dominated by non-conspecific plant communities. Seeds were also more likely to survive within Attalea aggregations if they passed through tapir guts and thus were protected by burial in feces. Previous work has shown that seeds deposited in tapir latrines give rise to higher density aggregations of seedlings and juvenile palms than seeds dispersed near parent aggregations or at random sites in the forest. Based on the results of our work with Attalea seeds and seedlings, we propose a model to explain how long-distance dispersal can create and maintain conspecific tree aggregations, a phenomenon which cannot be explained by the Janzen-Connell model of seed dispersal and survival
KEY WORDS: long distance dispersal, tropical tree diversity, seed shadows, tapirs