Herbivory in Complex and Simple Tropical Successional Ecosystems

Abstract

To investigate the relationship between herbivory and floristic complexity, we measured losses to herbivores in four 0.1— to 4—yr—old tropical ecosystems: (1) unmanipulated successional vegetation, (2) successional vegetation with higher plant diversity than the unmanipulated succesion, (3) an ecosystem of investigator—controlled species composition, designed to imitate the physiognomy and species richness of the successional vegetation, and (4) monocultures of maize, cassava, and Cordia alliodora. We measured herbivory rates (loss of leaf area per day) on dominant plant species in each system and aggregated over species to estimate rates for plant communities. Although herbivory rates varied widely among species, losses to herbivores in terms of mass of leaf tissue lost per unit of ground area were approximately equal in the four systems, 71.5 to 78.5 g°m—2. yr—1. Ecosystems with greater plant species richness lost a lower proportion of available leaf area and exhibited lower temporal variability in herbivory. Species—rich ecosystems had relatively constant, predictable rates of herbivory due to counterbalancing of low rates on some species with high rates on others. The rate of herbivory on any species was strongly influenced by the nature of the surrounding vegetation. Although surrounding vegetation often conferred protection upon potential pest targets, in some cases a plant species experienced increased susceptibility to herbivores through association with other species.