GENOTYPIC VARIATION IN LEAF DAMAGE IN PIPER ARIEIANUM (PIPERACEAE) BY A MULTISPECIES ASSEMBLAGE OF HERBIVORES.

The shrub Piper arieianum (Piperaceae) has a diverse herbivore fauna (95 species total) in Costa Rican rain forest. The effect of plant genotype on leaf damage by individual herbivore species and total leaf area removed was studied in P. arieianum through a cloning experiment. Damage patterns were measured over 3.5 years for two plots, four genotypes per plot, in the understory of lowland rain forest. In both plots, there were significant differences among genotypes in total leaf area missing throughout the study period. Rankings of genotypes based on overall damage remained constant over time in plot 1 but changed in plot 2. Certain individual herbivore species caused significantly higher damage in some genotypes than in others; the change in genotype rankings in plot 2 was associated with increased damage to particular genotypes by specific herbivore groups. The genotype most heavily damaged by a given insect species varied depending on the herbivore species; thus, resistance to one herbivore species did not necessarily confer resistance against all species. Those herbivore species causing the greatest proportion of damage for a given plant changed over time. Because total damage resulted from the summation of losses to individual herbivore species, whether an individual plant lost more leaf area than its neighbors depended on the relative abundance of the herbivore species at any one time. Finally, for a portion of the study period in each plot, more heavily damaged clones grew less than lesser damaged clones. Together with previous reports that naturally growing plants differ significantly in damage and that these differences are sufficient to cause fitness differences, the results presented here suggest that the herbivores of P. arieianum represent a selective force for changes in resistance but that this selective force changes both in intensity and quality over time.