O papel de forças top-down e bottom-up na organização das comunidades de insetos herbívoros e formigas em ambientes menos heterogêneos

Abstract

CHAPTER I _ The Trophic Cascade Theory has been considered a good criterion to explain the organization of herbivorous insect communities in tropical ecosystems. Considering this theory, we test the following predictions: (i) the abundance of host species and plant richness in the plot affect in a positive way the diversity of sucking herbivorous insects and the diversity chewing herbivorous insects, respectively, and (ii) an abundance of ants negatively influences the diversity of sucking and chewing herbivorous insects. The samplings were made in 16 plots through the beating technique in Erythroxylum suberosum and Qualea parviflora. An abundance of 71 ants and 158 herbivorous insects were sampled. Sampling in E. suberosum showed that the abundance of ants affected the diversity of sucking insects and that only the interaction of plant richness and ant abundance variables affected the diversity of chewing insects. In Q. parviflora, the density of this plant in each plot affected the diversity of associated sucking insects. In addition, the interaction of variables abundance of ants and abundance of Q. parviflora influenced the diversity of chewing insects. Our results indicate that there is no predominance of bottom-up or top-down forces in the organization of herbivorous insect communities in an area of tropical savana, suggesting that these forces are guild dependent. CHAPTER II _ Ants are important agents for structuring communities and maintaining terrestrial ecosystem services. Several papers suggest that ant communities can be organized by the heterogeneity of the environment and by interspecific interactions. In this study, the following hypotheses were tested in a regenerated cerrado environment: (i) vegetation structure negatively affects ant diversity in less heterogeneous habitats, and (ii) interspecific interactions regulate the organization of ant communities in stressed habitats. Ants were collected using the plot method in three distinct periods (February, April and June 2016), and a total of 457 individuals belonging to 17 ant species were sampled. The richness and abundance of the collected ants were negatively influenced by the average plant height of the plots and the observed C-score value indicated that communities can be structured by deterministic processes, such as interspecific interactions. This study suggests that the role of biotic and abiotic factors in the organization of the ant community is habitat-dependent. Thus, in less heterogeneous habitats ant diversity is negatively affected by vegetation heterogeneity and interspecific interactions, being these factors importante for the organization of ants communities.