Patterns and correlates of interspecific variation in foliar insect herbivory and pathogen attack in Brazilian cerrado

Abstract

Patterns of insect herbivore and leaf pathogen attack are described for 25 plant species (10 trees, 10 shrubs and five herbs) at a Brazilian savanna (cerrado) site. Plant and leaf traits were correlated with interspecific variation in attack by herbivores and pathogens in order to account for differences among plant species. Across all species, pathogen damage was 1.5 times higher than insect damage (17.3% vs. 6.8%, respectively). Most insect damage occurred to young leaves while they were expanding (end of the dry season). In contrast, pathogen attack was low on young expanding leaves at the end of the dry season, increased as those leaves matured in the wet season, but continued to increase through the next dry season. Protein-binding capacity was negatively associated with interspecific differences in insect damage to mature leaves. Protein availability and plant height were positive predictors of pathogen attack among plant species, while leaf expansion rate was a significant negative predictor. Interspecific differences in leaf phenology had little effect on the amount of damage caused by either insects or pathogens. However, new leaves produced during the wet season suffered less insect damage than leaves produced during the dry season, the time of greatest leaf production. Timing of young leaf production affected pathogen attack but the season of escape depended on plant species. In contrast, there was no evidence for escape in space as common species were less likely to suffer high pathogen attack than rare species. New and mature leaf toughness, and time for a leaf to reach full expansion all increased from herbs to shrub to trees, while mature leaf nitrogen decreased in that order.