Gradientes experimentais de diversidade influenciando herbivoria e interações inseto-planta em comunidades vegetais

Abstract

There is evidence that biodiversity directly influences or correlates with functions and services offered and regulated by ecosystems. In addition, plant diversity can affect aspects related to higher trophic levels, such as abundance and diversity of herbivore insects, herbivory patterns, and multitrophic interactions between plants, herbivores and their natural enemies. Therefore, this thesis examines how herbivory by insects can be affected by the diversity of plant species, by the diversity of functional characteristics of the plant species, as well as investigates how the configuration of the interaction networks between herbivore insects and plants may change over time. The study was performed in large-scale experiments in the Brazilian Caatinga and in Germany grasslands. In these experiments, plant communities were constructed with different levels of plant diversity. Chapter 1 studies how insect herbivory affects plant mortality and is affected by plant diversity in a Caatinga restoration program at the Brazilian semi-arid region. The results indicate that plant diversity at this early stage of restoration does not affect herbivory rates. It was also verified that the presence of herbivore insects did not jeopardize the initial establishment of plants during the Caatinga restoration, hence, it is not necessary to use any insecticide to combat possible pests that could harm the restoration. Chapter 2 studies the characteristics of the interaction network between insects and plants in the first two years of the Caatinga restoration experiment. The number of links was higher in older communities, as well as they seem more nested compared to young ones. The presence of highly generalist insect species are evident in these communities, and some plant species act as hubs of interaction in the networks. Chapter 3, conducted in Germany, discusses how insect herbivory can be influenced by both plant diversity and plant morpho-functional traits. A positive relation between plant richness and insect herbivory rates was found. Furthermore, herbivory rates are influenced by seasonality. However, functional diversity and species compositions grouped sorted by different functional traits (species pools) did not affect herbivory.