Influence of Flood Levels on the Richness and Abundance of Galling Insects Associated with Trees from Seasonally Flooded Forests of Central Amazonia, Brazil

We reexamined three hypotheses - “Nutritional stress hypothesis,” “Hydric stress hypothesis,” and “Plant species richness hypothesis” – which addressed galling insect abundance and richness in the canopies of igapo and varzea forests, considering different flooding levels (high and low quota). The collections were made at the Mamiraua and Amana Reserves, Brazil. In the varzea 26,244 galls were collected, corresponding to 297 species of galling insects; 23,994 galls were sampled in the igapo and identified as 235 galling species. The forest type and habitat (flooding level) had no significant effect on galling insect abundance. However, the interaction between these explanatory variables accounted for the variance on galling insect richness (GIR). High/low igapo categories presented larger values of the ratio between galling insect richness and tree richness, when compared to high/low varzea forests. The number of tree species was responsible for 82% of the variation in varzea GIR, while in the igapo a smaller value - 70% - was observed. Our findings indicated that local nutrient availability (igapo and varzea), flood levels, and their interaction affect both insects and plants, as well as their ecological relationships.