PARENT SESSION
Poster Session 2: Forest Ecology
Monday, August 8, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal

Direct and indirect effects of mutualists and antagonists on plant reproductive success in Rapatea ulei: SEM and complex natural systems.

McCain, Christina^{*,1, 2}, ¹ University of Miami, Coral Gables, FL² Biological Dynamics of Forest Fragments Project - INPA, Manaus, Amazonas, Brazil

ABSTRACT- A large body of ecological work demonstrates that individual plant-animal interactions such as plant-pollinator, plant-herbivore, and plant-seed predator interactions affect plant reproductive success at the individual, population, and species levels. Traditionally, different types of interactions are studied in separate lines of inquiry, however no plant-animal interaction exists in isolation in its natural ecological setting. A single plant species has a myriad of interactions with various animal counterparts – both mutualistic and antagonistic. This study addressed a complex set of ecological interactions between a single plant species and numerous insect mutualists and antagonists across intact and disturbed habitats. The herbaceous plant Rapatea ulei (Rapateaceae) occurs in riparian wetlands in Central Amazonian terra firme forest. The primary pollinators of R. ulei are euglossine bees. Bud herbivory, pollen robbing destructive to anthers and pistils, and ovary predation by drosophilid larvae also occur simultaneously at inflorescences and affect reproductive success. I used structural equation modeling to quantify the numerous direct and indirect effects of mutualists and antagonists in this system. This approach is extremely useful in complex systems, where experimental isolation of effects is limited or impossible. In intact forest, the empirical data fit the model of hypothesized relationships well (² = .12.43, df = 13, p = .49) and showed that two primary interactions accounted for plant reproductive success, while other interactions showed little relationship. Reproductive success was most affected by pollinator visitation rate and drosophilid damage. Other types of herbivory, which showed obvious potential for important negative effects on success were not significant. The model for intact forest did not, however, describe the relationships in deforested sites, where floral herbivores had strong significant effects on reproduction. Nearly 25% and and 53% of the variation in reproductive success was explained by plant-insect interactions alone in intact forest and deforested sites, respectively. Both models demonstrate that variability in these interactions had a large effect on this important component of plant fitness.

Key words: plant-insect interactions, Rapateaceae, seed production, structural equation modeling