PARENT SESSION
Poster Session #73: Plant Demography.
Friday, August 9. Presentation from 8:00 AM to 9:30 AM. Exhibit Hall B & C, TCC

Chemical defense and the demography of tropical cloud forest seed banks .

Hull, Adrienne^*,1, Rotman, Garth¹, Veldman, Joseph¹, Garcia-C., Mauricio¹, Mungall, William¹, Murray, Greg¹, ¹ Hope College, Holland, MI

ABSTRACT- Seeds of some pioneer plants accumulate in cloud forest soils at Monteverde, Costa Rica to densities orders of magnitude higher than the annual seed rain, while others remain viable for less than a year. Field experiments with selective predator and pathogen exclosures implicated predators (rodents and arthropods) as major sources of mortality for some species, and pathogens for others. One tested species lost viability rapidly even when protected from both predators and pathogens. We tested the hypothesis that differences in seed survival are due to differences in the effectiveness of defensive chemicals. Focusing on three species with long-term seed banks (Bocconia frutescens, Phytolacca rivinoides, and Guettarda poasana) and three species with short-term ones (Witheringia meiantha, Cecropia polyphlebia, and Urera elata), we assessed methanol seed extracts for arthropod toxicity (with brine shrimp bioassays) and fungal growth inhibition (using a poisoned medium technique). We also assessed palatability of B. frutescens, P. rivinoides, and G. poasana seeds to rodents. Only B. frutescens was highly toxic to arthropods, but P. rivinoides and G. poasana exhibited significant inhibition of pathogenic fungi. B. frutescens and G. poasana were the least palatable to rodents. Our results suggest that species composition of soil seed banks at Monteverde are indeed heavily influenced by predators and pathogens, the effects of which are mediated by seed chemistry.

KEY WORDS: pioneer plants, seed bank demography, seed predation, tropical cloud forest